January 22-25 Potentially Historic Winter Storm

A potentially historic winter storm looks to be unfolding for portions of the Eastern U.S.

Tropical Tidbits

A low pressure system is forecasted to develop in the South US and push northeastward to the area just offshore the Mid-Atlantic, with this coastal storm fully unfolding around January 23rd-24th. The above image shows the GFS 500mb geopotential height contours and mean sea level pressure values for the morning of January 24th. We see the snowstorm located fairly out to sea, at approximately 985 millibars. This track would produce the snow map below, taking this solution verbatim.

Tropical Tidbits

This solution would bring about 6-12" of snow to the Kentucky and Tennessee region, extending into extreme southern Indiana and a good chunk of southern Ohio. We also see similar amounts into northern Arkansas and southern Missouri, as well as North Carolina. Amounts on the order of 12-24" are outlooked for West Virginia, particularly the southern part of the state, into the majority of central Virginia, New Jersey, and eastern Pennsylvania into southern New York, with some slightly lower amounts further east into Massachusetts. Long Island is also forecasted to receive upwards of 12" if this solution were to verify.

Tropical Tidbits

To emphasize how critical the placement of this system will be, take a look at the ECMWF model's 500mb geopotential heights and mean sea level pressure values for the morning of January 24th, the same timeframe as the GFS graphic. We see the system at 984 millibars, pretty similar to the GFS, but the system is clearly displaced further west. Given how anomalously warm the Atlantic currently is, this shift could easily push those two to three feet amounts inland, and leave the coastline with rainy conditions. This run of the ECMWF has snowfall amounts of over 30" in central Virginia, but lesser accumulations the further north and east you go.

Tropical Tidbits

The GEM model shows amounts in the 6-12 inch range for most of Missouri into the southern parts of Illinois, Indiana and Ohio, as well as much of Kentucky and northern Tennessee into western North Carolina. Amounts in excess of 30" are forecasted from Maryland into Pennsylvania, certainly an incredible amount of snow, but not entirely off the table given how strong and persistent this system may end up being. Again, the placement of this storm will be critical to who gets the heaviest accumulations, and we likely won't know who will receive this jackpot until the storm is actually happening.

Tropical Tidbits

One last bit of advice, do not bite on any particular model run for this storm. The strength of this storm, as well as how long-lasting it will be, among other factors, makes me way too uneasy to trust any single solution, hence why I presented a plethora of models here. The above graphic shows GFS ensemble spread in MSLP values for this storm. The warmer colors to the left and right of the system indicate increased uncertainty with where the storm will track. Again, this emphasizes how no single solution is set in stone, and thus should not be taken at face value. A lot of change will happen in the next several model cycles, and the heaviest amounts could plausibly shift a substantial bit as these changes unfold.

To summarize:

- A potentially historic snowstorm is forecasted to occur along the East Coast over the January 22-25 period.
- Currently, the Maryland/Virginia/Pennsylvania region is on track to receive the heaviest amounts.
- The heaviest accumulations could reach or exceed 30".
- Enough uncertainty still exists to change the storm track substantially, as well as shift the heavy snow axis and amounts.

Andrew

January 9-12 Potential Winter Storm

There appears to be the risk for a storm system to impact the East US, particularly the Northeast, in the January 9-12 timeframe.

Tropical Tidbits

We'll first go over the forecast of the storm, and then get into it at a more analytical level. This forecast panel shows the 18z GFS forecast of precipitation type and intensity, as well as mean sea level pressure contours and 1000-500mb thickness values for the early morning of January 11th. We see a strong storm system just offshore the Northeast, producing widespread moderate to heavy rain right along the coast from New Jersey on northeastward, with light snow located in inland New York into east Pennsylvania. This solution could give copious amounts of rain and/or snow to the East Coast.

As expected, the internet is biting hard on this storm, given it could be the first real wintry system for the East this winter. Not to burst anyone's bubble, but below explains why I'm not expecting a real snow threat with this storm, and why not to bite on any forecasts yet.

Tropical Tidbits

This graphic shows us the 500-millibar vorticity values, forecasted for 12z (6 AM CST) today, Monday. That red box, all the way out near the Aleutian Islands, encompasses our storm system. That's right, the system that people are looking at is currently hundreds of miles away, closer to Russia than mainland United States. That's the first sign that we shouldn't take any model guidance at face value right now. Heck, the latest 00z GFS run came in and showed the storm pushing well out to sea, not even affecting most of the East US. I just chose to show that 18z GFS graphic so I could show what I'm talking about, and to make a few points, like this one.

Additionally, check out all the pieces of energy out ahead of our main system. If you count closely, just looking at this graphic, I can identify at least three separate storm systems downstream of our system of interest near the Aleutian Islands. Three systems is a lot for model guidance to sort out, and it doesn't help that one of those systems is also well out at sea, not even close to the radiosonde network which would help model accuracy. In sum, models are going to suffer a lot with this storm, both with the distance the storm is from the U.S., and how many systems are downstream of our storm itself.

Tropical Tidbits

This next point is specifically for the snow enthusiasts in the Northeast already getting excited for this storm. This is the 850-millibar temperature forecast for the morning of January 9th. At this point in time, our system is located somewhere in the South Plains, though it is not well-shown on this map. That's alright though, because we're looking at this image for the temperature spread across the Central and East US. All colors green and warmer are temperatures above freezing at this layer of the atmosphere (about 5,000 feet off the ground). That means that most areas east of the Mississippi River, save for Maine, Vermont, and New Hampshire, should be comfortably above freezing in the couple of days, even several hours prior to the storm actually beginning to impact the East (if it does at all).

For a good snow set-up, no matter where you may live, you want an established cold air mass before the storm begins. We saw that guideline in play with our last storm system, which dumped copious amounts of snow in the Plains into Iowa and Wisconsin, even laying down a few inches of sleet near Chicagoland. It was all that sleet and freezing rain that fell because there was no antecedent cold air mass. This go-around, we also will be lacking a pre-established cold air mass, and that really concerns me with snow prospects.

CPC

While I'm not set on the idea of a snowstorm, I am open to the concept of this actually being a storm for the Northeast. The North Atlantic Oscillation (NAO) will be negative when this storm occurs, albeit only slightly negative. This should encourage the storm to curve up the coast, though just how much 'encouragement' there is remains in question. It's completely plausible the storm goes straight out to sea, as the 00z GFS portrayed, and it's also possible it curves up the coast. I'm not confident in it going one way or the other right now, but both solutions are plausible.

To Summarize:

- There is the chance for a wintry storm system in the Northeast between the January 9-12 timeframe.
- Personally, I see a very realistic chance that this storm produces more rain than snow as a result of no antecedent cold air mass.
- Model guidance should not be trusted this far out.
- This storm could plausibly go out to sea rather than up the coast.

Andrew 

Winter Coastal Storm Threat Enhanced From Warm Atlantic Waters

It does appear that the threat for significant East Coast winter storms is on the rise, as we have seen rapid and significant warming of the Atlantic waters along the coastline in the last few weeks.

ESRL

The above image shows daily sea surface temperature anomalies for September 15th. While there are a number of variables we could analyze in depth, I want to focus on the situation unfolding in the central Atlantic today.

Take note of strong positive SST anomalies from the East Coast through Nova Scotia, partially reaching into the open waters of the Atlantic before being stopped by a swath of below-normal SST anomalies west of Europe. These well-above-normal water temperatures could be a focal point for the coming winter.

Coastal storms that develop along the East Coast can turn into Nor'easters, infamous for dropping massive amounts of snow on inland Northeast communities, and sometimes large rain amounts along the coast. If we are to see this warmer than normal body of water maintain itself along the East Coast, both in position and strength, it's quite likely we will see an enhancement of any coastal storms that do develop along the East US. This would occur as the warm waters feed additional moisture and energy into the storm system, increasing precipitation and strengthening the storm system.

To Summarize:

- Warmer than normal water temperatures off the East Coast may increase the threat for stronger coastal winter storms in the coming cold season.

Andrew

Anomalous Upper Level Low to Deliver Intense Cold in East US

An anomalous upper level low connected to the swirling mass of cold air in the Arctic looks to deliver a punch of brutally-cold air, impacting the East US the strongest.

PSU
Click images to enlarge

The above image shows the GFS ensemble mean spread forecast for the 500-millibar field on the top panel, with increased spread/uncertainty among ensemble members shown by shaded colors. That spread can also be seen in the individual member colored lines. The bottom panel shows anomalies for the 500-millibar field, with cool colors indicating negative anomalies, and warm colors depicting positive anomalies.

In this image, we note a strong upper level feature pushing south from Canada, with anomaly values reading 3.27 units below normal, maximized in western New York into western Pennsylvania as the purple colors show. Judging by the numerical denotations on that bottom panel, 500-millibar values could flirt with the 500-dm benchmark along the US/Canada border, indicative of a very strong (and very cold) upper level low.

Tropical Tidbits

Forecasts from computer models suggest sub-zero temperatures will be the theme throughout a significant swath of the North US. Latest guidance suggests temperatures in west New York and Pennsylvania will easily drop below -10 degrees Fahrenheit, with some locations getting very close to -20 degrees F. Locations further to the west, particularly in the Midwest and Great Lakes, may also come close to -15 degrees, with some areas dropping down to that -20 degree F benchmark. All in all, this is looking dangerously cold, potentially life-threatening.

To summarize:

- The first part of a multi-wave cold blast looks to impact the North US this weekend.
- Cold weather will be maximized in the Northeast, where temperatures could reach lows of -20 degrees Fahrenheit.
- Travel is strongly advised against due to the life-threatening nature of this cold air.
- Make sure to seek out assistance now for neighbors, friends, and/or family that may have trouble sustaining heat in their homes, or could be adversely affected by this cold.

Andrew

Upcoming Pattern Very Favorable for East Coast Snowstorms

The upcoming pattern appears to be very favorable for snowstorms along the East Coast.

Tropical Tidbits

The above image shows the 500mb geopotential height anomaly field over North America, forecasted by the GFS Ensembles from February 11th to February 16th. In this graphic, we see a strong upper level low dipping down over the Bering Sea, forcing a strong ridge to blossom along the Western US. A Rex Block then forms in the Southwest, as an upper level low slides under the ridge. Usually, a Rex Block upstream creates zonal flow downstream, but instead of rather calm weather in the East US, we see a deep upper level low pushing its way into the Northeast. This looks to be the pattern for the next 2 weeks or so.

In this sort of pattern, sustained northwest flow (winds from the northwest) often leads to a 'clipper train', where a multitude of Alberta Clippers slides southeast-ward into the Central US. These clippers can then move east off the coast, and can intensify to produce heavy accumulating snow for the East US. I believe that this is a possibility, and could happen more than once in the next couple of weeks.

Unisys

A look at sea surface temperatures shows how potent this environment is. For now, we'll focus on the East Coast. Notice all the oranges and reds immediately along the coastline, extending a bit east. Those are very warm waters, with well-above normal anomalies being detected. Consequentially, any clippers that move off the coast and threaten the East will have unusually warm waters to work with, which could very well enhance snowfall totals.

To summarize:

- The upcoming pattern is favorable for accumulating snowfall in the East US.
- This pattern may support more than one event of plowable snow.
- Extreme cold may affect the Northeast, at times.

Andrew

February 10-15 Potential Winter Storm

I'm watching for the potential for wintry weather in the February 10-15 period.

Tropical Tidbits

The image above shows 500mb geopotential height values for the morning of February 5th, with mean sea level pressure (MSLP) contours superimposed. In this graphic, we see two areas of low pressure over the Western Pacific. The more dominant system is located south and east of Japan, with another piece of energy just west of this island nation. In the forecast hours after this graphic, it appears the energy west of Japan transfers to the storm east of Japan. From there, the dominant low moves generally northeast, away from Japan. When we use the Typhoon Rule, which states weather phenomena occurring over Japan is reciprocated in the US 6-10 days later, a storm in the US might be expected in a February 10-15th period, adding a day for some uncertainty I have on timing. Additionally, the transfer of energy over Japan tells me we could be looking at a transfer scenario from the Midwest/Great Lakes/Ohio Valley into the Northeast.

ESRL

We can take a look at teleconnections to get a glimpse at what this storm might do. For this post, we'll pay attention to the top-right North Atlantic Oscillation (NAO) outlook. Notice how the index rises from negative to neutral territory right in the timeframe of this potential winter storm. The NAO switching phases is known to be a red flag for snowstorms in the Northeast, as the risk of snow events in that area tend to rise when this switching of phases occurs. This could support the idea of a transfer storm to the Northeast, like the GFS showed (in a likely overdone projection) in its 12z forecast:

Tropical Tidbits

To summarize:

- Model guidance is indicating a winter storm may impact the country in a February 10-15 period.
- As of now, a transfer low from the North-Central US to the East Coast may be a likely solution.
- As usual, high uncertainty still exists.

Andrew

January 28 - February 1 Potential Winter Storm

We're watching for a potential winter storm in a January 28th through February 1st timeframe.

Tropical Tidbits
Click Images to enlarge

The above graphic shows mean sea level pressure (MSLP) contours superimposed on 500mb geopotential height values (colored shadings), valid from last Thursday morning. Last Thursday, we saw a positively-tilted trough forcing a rather strong low pressure system to form just east of Japan, dipping below the 1000 millibar mark on this image. When we apply the Typhoon Rule, which states weather phenomenon occurring in Japan is reciprocated in the US 6-10 days later, we come out with a potential winter storm in the January 28 - February 1 timeframe.

Instant Weather Maps

Initially, the ECMWF takes this system down through the Midwest and Ohio Valley, as the above image shows on the evening of January 29th. We see a minimum sea level pressure value of about 1008 millibars, if not a bit below that. This won't be a significant storm, per current forecasts, but could drop some wintry precipitation across the aforementioned regions.

Instant Weather Maps

By the evening of January 30th, the ECMWF model sees this storm transferring offshore the Mid-Atlantic, strengthening at an appreciable pace to a minimum sea level pressure value of ~997 millibars. This would likely produce accumulating snowfall for parts of the Northeast, as the GFS model is also alluding to, but again, nothing incredibly significant.

To summarize:

- A winter storm may affect the US between January 28th and February 1st.
- This storm may affect the Midwest, Ohio Valley, and Northeast the most, if at all, given the relatively-weak strength of this storm.

Andrew

January 19th Potential Heavy Snow Event - Northeast

Model guidance is indicating heavy snow may strike the Northeast, particularly in Maine, on January 19th.

Tropical Tidbits

The image above, off the latest GFS model forecast, shows precipitation type, mean sea level pressure (MSLP) and 1000-500mb thickness value projections for Monday afternoon, on the 19th. We see a storm system offshore New England with a minimum central pressure of about 991 millibars, dropping extensive precipitation across the region. This storm should move out quick enough so the event is over by Tuesday morning or early afternoon.

Tropical Tidbits

The snow map from this storm shows about 6-12" of accumulation in New Hampshire, with amounts then escalating to the 36" mark in Maine, which is where the storm is expected to reach peak intensity/impact. Prior to this storm, about 6" falls across the region, lowering the totals shown here. Despite that, this storm still looks to be impressive.

To summarize:

- A heavy snow event is expected to impact the Northeast on January 19th.
- Amounts of 6-12" may be expected in New Hampshire.
- Amounts of 12-24+" may be expected in isolated parts of Maine.

Andrew

January 21-25 Potentially Significant Winter Storm

It's looking as if a winter storm will impact the United States between January 21st and January 25th. As of now, this storm has potential to be a strong one.

Tropical Tidbits

The above image shows mean sea level pressure (MSLP) and precipitation values for the morning of January 15th over the West Pacific. In this graphic, we see a strong low pressure system moving up the eastern coast of Japan, delivering heavy precipitation to areas offshore of the island nation. A look at 500mb vorticity values (not shown) depicts this storm phasing with another piece of energy to strengthen and mature the energy into a substantial event.

If we recall that the Typhoon Rule states weather phenomenon occurring in East Asia is replicated here in the United States about 6-10 days later, we should expect a storm system, possibly strong, to hit the US in a January 21-25 timeframe. The orientation of this storm striking the east coast of Japan tells me it may come up from the South US and hug the East Coast here in the US.

Interestingly enough, model guidance is approving of this theory.

Tropical Tidbits

The new GFS (the old GFS model was retired with this morning's 12z / 6AM central time runs, and replaced by what was known as the GFS-Parallel model) is showing a storm system developing in the Southeastern US on January 23rd. Here, we see a large swath of heavy rain, likely containing thunderstorms draped across the Gulf Coast into the Mid-Atlantic, as well as a heavy snow swath spread across the Ohio Valley and into the Northeast. This is something like I would expect to see happen with the way our energy acts when it skirts around Japan in the earlier graphic we analyzed.

Tropical Tidbits

By the evening of January 23rd, we find our storm has moved offshore, dragging an impressive liquid precipitation shield behind it, which then drags behind it a very cold airmass to introduce the anticipated cold blast to close out January. A strong snow swath remains present, but the most intense snow appears to strike Long Island in New York, as well as other coastal spots. Lighter, but still impressive snows then impact more inland regions.

To summarize:

- A storm is expected to impact the United States between January 21 and January 25.
- This storm has the potential to be strong, per current guidance.

Andrew

Long Range Regional Outlook (Northeast & Mid-Atlantic): September 20-October 12

This is the premiere post of the Long Range Regional Outlooks, this one valid for the Northeast over the September 20th to October 12th period.

CMC

After examining long range ensemble guidance, a split became evident between the ECMWF/CMC ensembles, as well as the GFS Ensembles. Have elected to side with the ECMWF/CMC projections, as GFS Ensembles are generally going against the grain of the other two ensemble sets, as well as my own thoughts.

The CMC ensemble mean 500mb geopotential height forecast is shown above. As a general rule of thumb, depressions in the contour lines tend to indicate troughing and cold/stormy weather, while arcing of the contour lines indicates ridging of high pressure, as well as warm/quiet weather. In the image above, we see 500mb height contours valid for September 20th. We see a rather zonal flow (non-wavy pattern) set-up over the northeast Pacific, with the jet stream pushing into the west coast of North America. This is in contrast to the GFS ensembles, which predicted deep troughing in the Gulf of Alaska. There is some slight ridging in the Southwest, leading to some weak troughing across Central and Eastern US areas.

ECMWF

The ECMWF ensembles are shown above, with the 500mb geopotential height anomalies and contours shown on the left panel, as well as the 'spread' (degree of disagreement among the ensemble members) for this forecast of September 21st on the right. This forecast is similar to the CMC ensemble projection above, as we see the Pacific jet stream pushing into the Western part of North America.

According to the height anomalies and contours, we do see some substantial troughing in the Gulf of Alaska, though it is not to the degree of the GFS ensembles. We then see some weak ridging in the Southwest, as was also seen with the CMC ensembles, though it is suppressed. Some weak troughing evolves in the Central US before weak ridging in the East.

Tropical Tidbits

In the image above, valid September 17th, we see a swath of negative height anomalies overtaking Japan as a rather strong upper level low scrapes the nation to the north. Seems pretty mundane, sure, but the consequences here at home are far more than mundane. As has been discussed consistently for the past couple of years, the weather in East Asia can have a significant impact on weather here in the United States. Utilizing the East Asian correlation of ridging over Japan equals ridging in the US 6-10 days later, and the same situation with negative height anomalies, we can foresee long range weather patterns weeks out at a time. This mechanism is referred to as the Typhoon Rule, and states that weather patterns found at the 500mb level can replicate themselves over North America 6-10 days later after they appear over Japan.

If we use this rule for the Northeast, we might expect to see the northern parts of the region get some substantial cold around a September 23rd - 27th period. This fits in with the CMC and ECMWF ensemble projections, and is a reason why I disagreed with the GFS ensembles.

* The image used above is a forecast from the GFS ensembles, but the part I disagree with is for its forecast in the Northeast Pacific, not over Japan. Still, this part of the forecast must be monitored closely for the discrepancies described above.

Tropical Tidbits

Once again using this Typhoon Rule, we see the forecast on September 21st calling for continued deep troughing over Japan, now pushed deep into the country. Using the guidelines set forth for this rule, we might expect continued cold in the Northeast around the September 27th - October 1st period.

After going over all of the factors above, as well as extra analyzations not mentioned in this post, the outlook for the September 20th to October 12th period over the Northeast is as follows.

Temperature Outlook:

The Weather Centre
Temperature Outlook

Precipitation Outlook

The Weather Centre
Precipitation Outlook

I expect the Northeast to remain predominantly below normal for temperatures in the aforementioned time period, while precipitation should end up a bit below normal, close to neutral.

Andrew

Long Range Forecast for Late April, Early May

Let's examine the long range forecast for late April into the beginning days of May.

Long range analog guidance from the ESRL/PSD division, a special physics-based meteorology branch of the government weather service, indicates we will see troughing setting up in Western North America in late April as a strong upper level low drops into the Southwest, provoking high pressure out ahead of it in the Central and East US. This ridge out ahead of the upper level low will likely make for anomalously warm weather across the aforementioned sections of the country, a real treat in the face of such a nasty winter.

Beyond the last days of April, it is expected that the weather will take on a slightly cooler tone. In the wake of a Kelvin Wave currently pushing across the Pacific, enhanced tropical convection is expected to develop near the 60E Longitude demarcation, a classic Phase 1 MJO signal. When we see enhanced tropical convection in this Phase 1 signal, it typically means we can anticipate cooler than normal weather here in the United States.

I am a bit skeptical of this cold weather forecast, due to the response we're looking to see in East Asia around April 26th. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. In this image above, we see projected tropopause pressures, vector winds, and wind speeds way up in the middle-upper regions of the troposphere into the stratosphere. If we look to this forecast image, valid April 26th, and find Japan in the top left corner of the image, we can make out a bulge of orange pushing towards the center of this image. That orange bulge signifies the presence of a Rossby Wave. In simple terms, this Rossby Wave will 'break' over Japan and initiate an intensive warming spell. This may continue for some time, but if it does happen in late April, we would likely see the cooling effects of the Phase 1 MJO hurt, as this East Asian development would likely overrule it.

To summarize:
• A warm end to April is expected.
• A cool start to May is possible, but there are hints that the late April warmth may just carry over into May. More time is needed to investigate this potential.
• A severe weather event is possible in the final 7 days of April, due to the upper level low in the West US.

Andrew

March 26-31 Multiple Potentially Significant Snowstorms

I'm examining the idea of multiple significant winter storms over the March 26-31 period.

The above image shows a recent ECMWF forecast, projecting 500mb height anomalies over the North Pacific on March 20th, where blues and purples show negative height anomalies (cool and stormy weather), and oranges and reds depict positive height anomalies (warm and quiet weather). Looking towards the continent of Asia, specifically zeroing in on Japan, I marked two points of interest using the letter X. These X's denote the location of storm systems in the area. There is a storm system moving east over Japan, tilting negatively as it does so, and a storm to the west of Japan, just beginning to drop south and racing towards the country. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. The two storm systems both retain impressive intensities, with the bright purples indicating that both systems look to be strong.

About 18 hours later, we see that the situation over Japan has changed. The first storm system that was previously over Japan has shot north, influenced by the even-stronger system shown in green shades south of far northeast Russia. The second storm system that was previously racing towards Japan is now impacting Japan, maintaining rather-strong characteristics, as shown by the tinted purples over the country. This confirms there may be not one, but two storm systems in this timeframe.

Shown above is the ECMWF Ensemble mean forecast of 500mb height anomalies, over North America. The same color rules, where blues indicate stormy weather and oranges show calm weather, still apply. This forecast is valid on March 26th, the beginning of the five day period we're watching for these two potential storms. We see storminess evolving over the West Coast, shown by the darker blues just offshore of California, Oregon and Washington state. We see this provoking slight ridging in the southern Plains, well illustrated by the erosion of blues in that region. We also see an old friend in a piece of the polar vortex still sticking around in Canada. The storminess over the West Coast should enable the high pressure over the Southern Plains to gradually strengthen and push east, as it's possible we see a negative Pacific-North American pattern evolve, which is characterized in the image below.

Typical negative PNA pattern
NCSU

We also see how a lobe of the polar vortex still sits over Canada, as it has been doing for much of the winter, and should continue to do into spring. If this forecast were to verify, it wouldn't be too hard for the storm track to be suppressed, from the Midwest down into the Ohio Valley. This could favor areas that have been hit multiple times already this winter, including the lower Midwest and Ohio Valley regions.

The GFS Ensemble forecast for 500mb anomalies at about the same timeframe have a pretty similar pattern, even though they may seem different at first glance. The PNA remains negative, like the ECMWF ensembles project, as we see strong negative height anomalies over the West Coast. We also see a lobe of the polar vortex positioned in Canada, as we did in the ECMWF Ensemble image. The only 'difference' here is that the ridge we discussed in the ECMWF Ensemble image is more pronounced on this image, and located further east. This solution would likely still drive storm systems into the Midwest, but they would also be suppressed- just not as much as the ECMWF ensembles say they would be. This sort of projection would take the two potentially significant snowstorms into the Midwest and Ohio Valley, as ridging in the Southeast would deter an East Coast solution.

Caveat: The ECMWF projection that says we would get two major storm systems is a long range forecast, and has a chance of not verifying completely. There is a pretty good chance we would be seeing a potentially significant storm system in this timeframe, it's the idea of two storm systems instead of one that isn't really solidified just yet.

To summarize:
-One or possibly two potentially significant storm systems are expected in the March 26-31 timeframe.
-Both winter and severe weather modes would be quite possible with this event.

Andrew

March 15-19 Potentially Significant Storm System

I'm eyeing the March 15-19 period for what could be a significant storm system.

The image above shows ECMWF 500mb height anomalies from a previous forecast, valid on March 9th, which was two days ago. While this forecast is not current, and the forecast image above is not current either, we did see a big storm move through Japan on March 9th. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Using the image above, we can expect a storm in the US 6-10 days after March 9th, which would bring us to a March 15-19 storm. Not only that, but this forecast indicates the storm in Japan will be/was strong when it passed through, and this means that the storm we experience March 15-19 could very well be strong, too.

Shown above is the latest ECMWF ensemble mean forecast for 500mb height anomalies on the evening of March 15th. Interestingly enough, we see the ECMWF ensembles already have this storm in the Plains, meaning the idea of a big winter storm for this timeframe is becoming popular. The ensembles have a positive PNA pattern in place, meaning we see high pressure shooting north along the West Coast, with consequential storminess in the Plains. We also see ever-so-slight ridging in the Southeast, but this is suppressed by the piece of the polar vortex displaced over southern Canada. It looks like the ensembles want to develop a split jet stream pattern, which could open the door for phasing of storm systems. Despite this potential, I feel that any storm in this timeframe would either move east and possibly up the coast, though I'm a bit hesitant about that potential due to the polar vortex pushing down on the jet stream as well as the storminess over Greenland (which typically does not favor East Coast snowstorms). The other idea would be the storm moving north and hitting the Midwest/Great Lakes, but I'm also skeptical on this idea due to the polar vortex piece trying to suppress the storm (which could very well happen), as well as the lack of high pressure in the Southeast to force the storm north. We'll get a much better handle on this in coming days, but be warned that the March 15-19 period could see a potentially significant storm hit the US.

It is also worth noting that we could see some severe weather, though to which degree is to be determined.

Andrew

Impending Snowstorm to Drop 12"+ of Snow Tuesday and Wednesday

Note: This post will concern the March 11-14 Significant Snowstorm, but the title has been changed. If you find this sort of title better than the date and storm classification, or if you prefer the date + classification, leave your input in the comments below.

I'm carefully watching the next few days for a snowstorm that looks to drop a foot of snow or more on the United States.

We'll begin with an analyzation of the big picture of this storm. The model I will be using here will be the NAM model, as its low-resolution GFS counterpart appears to be suffering from some errors we will address later on in this post. The image above shows mean sea level pressure (MSLP) values, as well as precipitation values and high and low-pressure demarcations for Tuesday afternoon, tomorrow. We see a strong storm system in the far northeast corner of Kansas, bottoming out at 994 millibars and creating a heck of a pressure gradient over Nebraska. In Nebraska, we also see a precipitation shield breaking out, which could be accompanied by some harsh winds if that pressure gradient happens to meet up with the precipitation. Luckily, this forecast keeps the strongest winds just south and east of the inclement weather in northwest Nebraska.

In the late evening hours of Tuesday, we see that our storm system has pushed off to the east, maintaining both its tight pressure gradient and precipitation shield as it progresses east. Our storm is now at about 995 millibars, roughly the same strength as what we saw Tuesday afternoon in the image above. The 1 millibar difference really isn't anything to write home about in this situation. Typically, we might see a severe weather situation arising in the Plains and Midwest due to that tight pressure gradient, but that swath of precipitation down in Mississippi, Alabama and the panhandle of Florida indicate there's a storm system there (a closed low, to be exact) that will prohibit such a severe weather event from forming. At this point in time, accumulating snow should begin to fall over the Midwest.

By the time we hit the morning of Wednesday, March 12, we find that phasing has occurred with our storm system. What this means is that our original system has phased, or merged, with a system coming south from Canada to create a single, stronger storm. This is clearly displayed by the abundant precipitation breaking out over Michigan, Indiana and Ohio, and also shown by the tighter pressure gradient expanded across much of the Central and East US. It is also possible the western flank of the gradient is a bit amplified thanks to the strong high pressure in Canada, but that's not a big piece of the puzzle right now. At this point in time, potentially significant accumulating snow looks to be impacting the Ohio Valley.

Lastly, by the evening hours of Wednesday, we see the system has now transferred offshore, and is now putting down significant accumulating snow across the interior Northeast, leaving coastal areas (and even some inland regions) to experience rain or a mixing event.  The extreme pressure gradient remains in place, maximized in this forecast graphic over Pennsylvania and New York, as well as the rest of the New England area. After this, the storm exits the region, leaving quite a snowstorm in its wake. Check out the latest snowfall forecasts for this event:

To add some model variety, we'll also show the GFS snowfall forecast.

If you look at these maps and think something's not the same, you're right. There are some differences here. The primary difference is that the GFS is more south with the storm system than the NAM model. This is displayed well when looking at the beginning of the accumulating snow swath all the way back out in Illinois. The NAM model gives a generous 6" or more to Chicagoland, but the GFS only lays down a handful of inches across Springfield, IL.

After looking at all the data, I think it might be best to lean towards a NAM solution with the placement of heavy snow further north in the Great Lakes, but not too far north, if you know what I mean. Let's go over why.

The first red flag is the NCEP Weather Prediction Center's preferred track superimposed on an ensemble suite for this storm system. We see the NCEP WPC track for this storm in black, but it's obvious that their track is on the southern envelope of guidance. The heavy majority of ensemble members prefer to take this storm further north, into central or northern Missouri rather than southwestern MO. This would result in snow totals displaced further to the north, like the NAM says. But we can dig deeper than this. Let's keep going in our search for why these northern amounts are more preferred over the GFS.

Let's take a close look at the image above. Here, we see the NAM model projecting 300mb wind speeds in color shades and wind barbs, valid early Wednesday morning. If you look closely, you can spot two distinct jet streaks, or two areas of stronger winds than the winds around them. These are shown best by the yellows in Oklahoma and Kansas, as well as in far northern New England. These two jet streams form the classic coupled jet stream, as defined by Uccellini and Kocin in their studies. This coupled jet stream idealizes that there is a space between two jet streaks, where heightened divergence is found. In other words, in the space between two jet streaks, the atmosphere wants to create more precipitation. So, if we look above for the space between these two jet streaks, we can draw a line roughly from Missouri to Lake Michigan of where this increased divergence, or increased precipitation would be expected to appear. This would seem to put the NAM's snowfall placement 'in the right' when compared to placement of the GFS snow totals, at least in the Great Lakes region.

Also, take a look at what the 18z GFS does with the storm as it moves along the Ohio Valley.


If you watch the low pressure denotation as it moves from Indiana, it goes to the southeast rather than to the east. You might not think this is so odd, but when you compare it to the agreed notion that this storm will be moving west-to-east, a southward movement is rather odd.

Additionally, a convective feedback issue was observed as the system crossed east through Indiana, likely hampering the forecast for this storm. In this case, you may want to defer to the 12z GFS, as it is more logical in comparison to this run.

To conclude, a significant winter storm is expected for a good chunk of the US. Model guidance differs on placement of the snow, mainly in the Great Lakes, but it is agreed on that the Northeast will see a substantial snowstorm.

Andrew

March 11-14 Significant Snowstorm

I'm still looking at the idea of a significant snowstorm on the March 11-14 period.

An upper air analysis at the 500mb level of the atmosphere shows our storm system as the depression in the contour lines over the northeast Pacific, which tells us the system isn't onshore yet. The storm not being onshore means that model guidance will continue to change until the storm actually gets onshore. The reason being that National Weather Service offices release weather balloons twice a day, and the data those balloons gets goes into the models to enhance their forecasts. Thus, when the balloons are sent into the storm when it comes onshore, the models get a better handle on the storm, and that's why we tend to see a model consensus come about when the storm system in question comes onshore. We also see suppressed ridging over the Western US, which will impact the eventual track of this event, as we'll go over later.

Shown here is the GFS 500mb vorticity projection for the evening of March 11th. On this image, it seems our storm system is separated into two storms, located over Nevada and Kansas. In this case, the GFS model wants to take the westernmost portion of the storm and retrograde it into the ridge located along the West Coast. This piece of energy then closes off and separates from the other piece of vorticity that continues progressing eastward. This move is a bit suspect to me. It is well known that model guidance has the tendency to hold energy in the Southwest for too long, and this could very well be one of those situations where the GFS is too eager to bring a piece of the storm into the Southwest US.

By the time we get to the evening of March 12th, about 24 hours later from the image we just discussed above, we see a lot has changed. We now see that the storm has indeed separated into a closed system along southern Nevada and California, which is linked to its parent storm by an elongated lobe of positive vorticity draped across the Plains. We'll get to that parent storm in a second, but first let's go over the storm in the Southwest. The system has retrograded directly into the West Coast ridge, and has closed off in the process, leading to a Rex Block-style pattern, where we have a ridge directly north of a storm system. While the typical Rex Block produces a zonal flow (west-to-east flow) synoptic set-up across the areas downstream of the block (to the east of the block), the GFS prefers to initiate a northwest flow regime, with the West US ridging leading to deep troughing across the East US. This leads us into the parent storm, which is in its own category here. The aforementioned northwest flow has led to a phasing (merge) of the easternmost storm we saw in the second image of this post (the first GFS image we discussed) with a weak system originating from northern Canada. This comes as no surprise, with the northwest flow regime being very supportive of phasing should the opportunity arise. I'm a little skeptical on this idea, as models are notorious for phasing storm systems too eagerly. This could mean we actually see two weak, unphased systems when the March 11-14 timeframe comes around, but with guidance supporting this phasing more and more, I find that the positives for phasing outweigh the things going against it.

This is the ECMWF 500mb vorticity forecast for the evening of March 11, the same timeframe as the first GFS image we analyzed. In this model's forecast we see the two systems are still trying to split up, but are nowhere near as elongated as the GFS model portrays them to be. Rather, we see the two systems fairly well defined, with one over Utah and the other over Kansas.

The above graphic shows the ECMWF 500mb vorticity forecast for the morning of March 13th, about 6 hours after the second GFS image we analyzed. Here, we see a significantly differing view as to what happens. The ECMWF takes the westernmost system and does retrograde it into the Southwest, but it does so as an incredibly weak system, so the system does not become a closed low and the Rex Block cannot form. We see a strong lobe of positive vorticity extending across the southern Plains and Gulf Coast, before we arrive on the parent storm, which has phased with the Canadian storm. This solution also results in a snowy solution for much of the Northeast, and it is a viable idea. However, because this is a northwest flow regime, and the ECMWF model has performed poorly in northwest flow situations this winter, I'm not ready to buy in on this solution just yet. It will probably take another day or so before we can at least refine the solutions we have now to try and come across a more solid consensus.

Here's an overview of current model projections for snowfall.


Andrew

March 11-14 Potentially Significant Snowstorm

As I discussed back on February 25th, we're looking at the potential for a significant winter storm in the March 11-14 timeframe, narrowed down from the original March 12-17 timeframe.

The ECMWF model's 500mb vorticity forecast for March 12th is shown above, and we see the two ingredients for our storm on this map. We see the main piece of energy as an elongated swath of positive vorticity stretching from Nevada to Missouri, with our second player dropping south on the lee side (east side) of the ridge stretching across the West Coast. We also see a piece of energy in the Gulf of Mexico which will do its part to interrupt the severe weather aspect of this storm, which is why we'll be focusing on the snowy side.

The ECMWF develops a 997 millibar low centered over southern Illinois on the morning of March 12th, with overpowering high pressure to the north suggesting we aren't likely to see any big northward shifts with this storm in the future. Model verification confirms this idea. As far as the projected storm, this 997mb low is just the elongated system, not accounting for the system dropping from Canada which will eventually phase with the aforementioned system in Missouri.

By the morning of March 13, the system is rapidly deepening in the Mid-Atlantic as the two pieces of energy have begun to phase. This means that they are combining into a single storm system, which only intensifies the snow potential for this event. From March 12th's jet stream forecast, I would expect we see the system try to push east due to a rather zonally-oriented jet stream across the United States, which isn't that favorable for the system to shoot up the coast. However, by the time it hits the coast, the jet stream is essentially laying out the red carpet for the system to go northeast and affect the Northeast.

The snow map for the ECMWF would dump amounts of upwards of 12" across much of the Northeast, including coastal regions, while laying down over 6" in Ohio and a portion of Indiana. This would all depend on phasing of these two systems, which the folks at the National Centers for Environmental Prediction (NCEP) indicate may not be so likely. They indicate that models tend to phase systems too often, when in reality, they don't end up phased. This could be one of those situations, but I guess we'll just have to wait and see.

The GFS model, on the other hand, is much less enthusiastic when compared to its European counterpart. We see both systems shown above, valid for the same timeframe as the 500mb vorticity map we looked over at the top of this post, but in the GFS' case, the layout is different. The GFS model keeps the system back in the Southwest, on a positively-tilted axis, meaning the strongest vorticity values are pointing in a southwest direction. I have a feeling the GFS might not be grasping this system correctly. The NCEP agency also states that models in general have a bias to keep storms in the Southwestern US for too long, when in reality they eject from the Southwest quicker than forecasted. This would work in favor of the ECMWF's solution. However, the GFS does not phase the two systems, which results in noticeably less snow and precipitation in general. We'll need to watch both models for this system in the next few days, as both appear to be hanging on to one bias while letting go of another one. In this case, the ECMWF may be phasing the systems too eagerly but not holding the energy back in the Southwest, while the GFS looks to be keeping the system in the Southwest but not phasing the storms.

Andrew

Weekend Snowstorm Targets Midwest, Ohio Valley

I'm expecting a snowstorm to impact the Midwest, Ohio Valley and East Coast this weekend.

As the graphic above shows, I anticipate the heaviest snow to extend from northern Missouri through Illinois, Indiana, Ohio and into Pennsylvania and New Jersey. West Virginia and Virginia will also be impacted by heavy snow. I anticipate we see amounts somewhere in the 6-8" range over the Midwestern states I just mentioned, while areas along the East Coast have a higher upside, possibly near 12". With this storm comes the threat for freezing rain, and I expect this threat to reside from Arkansas into Kentucky, eastward through the Virginias. Pinpointing the location of freezing rain is difficult, and with model guidance still having numerous issues handling this event, do not be surprised if my forecast chances later today. I based this map off of the 12z GFS, seeing as the system has finally made it ashore and a general forecast with this layout appears to be the consensus at this time.

A look at enhanced water vapor imagery shows the storm system making its way onshore, throwing out massive amounts of moisture ahead of it, as the warmer colors show. The circulation of the storm remains just offshore of California, a bit east of that swath of dry air depicted in dark blues. As the system makes its way onshore, we should see model guidance improve and (hopefully) settle on a solution, as the weather balloons sent up by each National Weather Service office at 6 AM and 6 PM (central time) each day will be able to ingest data from the storm, which then feeds into the models to make a more accurate forecast.

There is some talk about model guidance underdoing precipitation in this storm, and also being too far south. The jet stream is predicted to be aligned in such a way that the storm would normally push further north than it is currently projected to go, and we would typically see the heaviest snow shifted to the north as well. However, with models standing their ground on the storm staying south, and both the northern and southern jet streams now "sampled" by those weather balloons, having been onshore for some time, tells me that the storm will most likely stay on its southern track. The under-doing precipitation claim is a bit more difficult to decipher. On one hand, model guidance is notorious for over-doing precipitation when you compare observed precipitation to forecasted precipitation, but in this scenario, we will have a strong jet stream and Gulf of Mexico moisture feeding into the environment, which would usually help enhance precipitation totals. I want to wait for a bit before making a call on that issue, because it'll most likely take a close analysis of radar trends to determine how model guidance has been handling that aspect of the storm.

Andrew

February 15-16 Potential Blizzard

It looks like there is now the potential for a blizzard this Saturday and Sunday.

The GFS model shows extreme wind speeds along the coast of the Northeast as another strong storm system rides up the coast in similar fashion as the storm that just ended for the East Coast. We see 10 meter wind speeds over 44 knots just offshore land, with widespread 25-35 knot wind speed forecasts at the height of this storm.

The GFS model indicates the storm will drop accumulating snow along the coast, as the 984 millibar low comes close to land. Despite the proximity of the low pressure system to the coast, the precipitation here will not be incredibly intense. Accumulation is expected, and the wind will be that of borderline-blizzard conditions, but the accumulation will not be significant.

The real fun begins overnight of Saturday into Sunday, as the GFS projects this storm will rapidly strengthen to drop significant snow accumulation on Maine, and this should continue into the day on Sunday. The system will be moving rather quickly, so while significant amounts are expected, it will not be a prolonged event. This also means good news for those of you who like to watch snow come down at high rates (i.e. 2 inches an hour or higher), as we'll likely see some pretty high snow rates in Maine from this storm.

This 6 hour snowfall forecast shows the intense snowfall overnight Saturday into Sunday, with the GFS depicting amounts as high as 12 to 14 inches of snow falling in that 6 hour period. If you were to average that out, it would be equivalent to 2" of snow falling every hour, but as we all know, snow does not fall in uniform and consistent rates like that. It's more probable that we would see very high snow rates (possibly 4" an hour at best) for a period of time, with lighter rates mixed in (i.e. 1" an hour or lower).

When all is set and done, here is the total snowfall put out by the GFS model. We can see those high amounts in Maine, but also some good totals in coastal portions of Massachusetts and Connecticut. Again, totals aren't looking to be too bad (I'm not so sure we see the GFS' predicted 10" of snow hit those areas in MA/CT), except for in Maine. The wind will certainly make it feel like a big snowstorm for those further south, though.

The NAM model has a different take on this event, bringing heavy snow to only the extreme eastern portion of Massachusetts, with that jackpot in Maine also moved to the east. Considering we saw the snowstorm along the East Coast a few days ago also further east than what model guidance suggested, it's possible we see a solution like this work out.

I'm wrestling with which solution I like better in this case. On one hand, we have the GFS solution, which seems somewhat-reasonable (compared to the NAM) with the slightly-lower inland snow amounts, but on the other hand, the NAM model being to the east may verify, considering the most recent East Coast storm appears to have been further east than modeled. Needless to say, this forecast will see some fine-tuning in the hours ahead.

Andrew

February 15-16 Potential Coastal Snowstorm

Yet another snow event is possible for the East Coast, with this next threat coming in the February 15-16 period.

WeatherBell

The GFS model indicates we will see another trough develop in the Southeast, with an uncanny resemblance to the storm we are currently fighting through along the East Coast. The GFS sees this storm coming about as a result of the strong-yet-suppressed ridging in the West US, which leads to a west-northwest or northwest flow across the US, a favorable pattern for East US snow events.

The GFS model brings a 984 millibar low pressure system along the waters just off the East Coast, dropping snowfall in the eastern portions of North Carolina, Virginia, Massachusetts, Maine, and all places in between. This snapshot, valid on the evening of February 15, shows the heaviest snow staying offshore, but moderate snow still being able to impact the easternmost parts of the Northeast. As of now, accumulations for regions up to Maine look to be in the 2-5" range.

The storm system really gets going when it approaches Maine, with the MSLP for this storm clocking in at a minimum of 973 millibars. We see 6 hourly snowfall amounts in eastern Maine approaching 12", which would average out to 2 inches per hour for those 6 hours overnight from February 15 to 16. Now, heavy snowfall doesn't fall for 2 inches an hour at that steady rate- my guess is that we would see a period of intense snowfall rates (i.e. 3" an hour not unreasonable) with some lighter snow rates mixed in.

Only a slight shift west or east could flip the forecast- stay tuned for more details about this potential snowstorm.

Andrew

February 12-14 Potentially Historic Winter Storm

Things appear to be coming together for a potentially historic winter storm, though model biases mean intense model forecasts are likely overdone.

This image shows the ECMWF model's snowfall forecast for the next 144 hours, and it is not that hard to see the big storm system this model believes will strike a large portion of the Eastern US. We see that the ECMWF model begins by dropping heavy snow in excess of 12" on the areas of northern Georgia and the Carolinas into western Tennessee and Kentucky, before amounts max out near 2 feet in the Virginias. Heavy snow continues into the Northeast, with widespread 12-18" totals across the map for that region.


The ECMWF model has remained consistent on this idea of a major winter storm for the East Coast, including the Southeast. These big amounts are relatively unchanged from previous forecasts, except for the 24" jackpot zone in the Virginias. The environment looks highly favorable for an East Coast storm synoptically, with a west-northwest flow solution prevailing over the contiguous United States. This is shown well by storminess in Alaska leading to strong yet suppressed ridging over the Southwest US. Considering northwest flow scenarios typically can lead to Northeast snow events, it is of little surprise that a strong storm system in the Southeast is able to shift northward and ride the coastline to produce heavy snowfall across the far Eastern US.

The CMC model (Canadian model) above shows heavy snow extending from far northern Georgia to eastern Canada, in a similar fashion as the ECMWF (though not identical). The heaviest snow hits Maine, where amounts flirt with the 16" benchmark, and the remainder of the East Coast stays within the realm of 6-12" or a little higher, as the model shows some higher totals in New Jersey and a few other coastal places.

Surprisingly, the CMC model may have shed its too-snowy bias in this forecast and is actually showing a more reasonable solution compared to the ECMWF. It does look like the crucial point will come when we determine how far south the storm system goes. In the ECMWF's forecast, the storm is a bit to the south of the CMC, hence the heavier snow totals located deeper into Georgia. In future forecasts, I wouldn't be surprised to see totals bumped up a bit along the coast, but other than that, this forecast isn't that far fetched in my eyes.

Lastly, we see the NAM model's snowfall forecast above. The NAM drops heavy snow amounts of over 12" in a large swath of Georgia in what would be a truly paralyzing snowstorm for those who went through the agonizing snow event in Atlanta just a couple of weeks ago. If we look at the NAM forecast further north, we see the heavy amounts extend into the Carolinas, and a strip of 24" to 31" snow amounts in eastern Virginia and the coastal portion of the Mid-Atlantic. The heavy snow then continues into the coastal New England area, but the full storm is not in the NAM model's forecast timeframe yet, so we cannot get total snow amounts in the Northeast yet. Regardless, it's clear that this event would be historic for those down south.

The NAM model is notorious for making forecasts laden with a noticeable too-snowy bias. I expect that this forecast is well within that bias, and it would be wise to cut totals in half or so to be safe until we get closer to the event. Amounts in the Southeast also are unlikely to end up as high as they are shown- I would expect totals maxing out at 6" at this time.

Andrew