February 15-19 Potential Snowstorm and Ice Storm

The February 15 through 19 period is increasing in likelihood that we will see a winter storm, potentially with an ice storm component.

Tropical Tidbits
Click images to enlarge

The image above shows the GFS forecast for precipitation type over the United States for the morning of February 16th. Here, we see precipitation breaking out over the Southern Plains and along the Gulf Coast as a low pressure system advects northeast-ward. In this forecast, we see a snow shield placed from southern Illinois into Missouri, Arkansas, and the Tennessee/Kentucky area, with rain blossoming in Texas, Louisiana, and southern Mississippi. We also see a rather broad swath of sleet, potentially freezing rain in southeast Oklahoma, central Arkansas, and northern Mississippi. This freezing rain/sleet delineation could prove to be a serious issue for those in the South, especially with memories of the ice storm from last year still fresh.

Tropical Tidbits

By the evening of February 16th, the low pressure system responsible for this precipitation is trekking along the Gulf Coast, located along the Mississippi/Alabama border in this graphic. A rain shield encompasses Louisiana, Mississippi, and a good chunk of both Alabama and Georgia. Snow is falling in eastern Tennessee, the western Carolinas, and extreme western Virginia, with a small band of freezing rain / sleet in northern Mississippi and Georgia. It's encouraging to see the freezing rain shield shrink from our last image, but as freezing rain is so tricky to predict, I wouldn't take that part of this forecast verbatim.

Tropical Tidbits

By early morning on February 18th, the storm has transferred offshore and is beginning to strengthen over warm waters along the coast of the East US. Snow continues to fall in much of North and South Carolina, with rain prevailing in southern Georgia and much of Florida. Heavier bands of snow are already impacting coastline locations in the Mid-Atlantic and Northeast, with New Jersey on the northern fringe of this heavy snow shield. From there, the storm continues north and east.

Snow accumulation charts are unreliable in this case, as some methods for snowfall will accidentally count freezing rain and sleet as snow, unrealistically amplifying snow totals. Thus, it would be unwise to show a snow total chart for those in Arkansas, where that unrealistic amplification of totals is likely to occur.

WxCaster

I want to now look at the forecasted freezing rain accumulation chart from the short-range NAM model over the Eastern US. In this chart, we can see where freezing rain is most likely to occur. Again, because freezing rain is so hard to predict in advance, take this with a relative grain of salt. Regardless, let's see who may be affected. The highest freezing rain totals appear in western South Carolina, where accumulations of 0.50" to 0.75" could be found. Significant accumulations of 0.25" to 0.50" extend through the rest of the Carolinas, and isolated spots of similar totals stretch back through northern Mississippi, Georgia and Alabama, all the way to southern Arkansas. While you shouldn't expect to see this chart verify exactly as-is, it gives you a good idea as to who may be affected by freezing rain from this storm.

To summarize:

- A storm system in the Southern US looks to bring wintry precipitation to states such as Arkansas, Mississippi, Alabama, Georgia, Tennessee, Kentucky, and the Carolinas.
- Accumulating snowfall is possible, particularly in Tennessee and Kentucky.
- Accumulating freezing rain is possible, particularly in southern Arkansas, northern Mississippi, Alabama, Georgia, and the Carolinas.

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

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 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

January 6-10 Potential Winter Storm

Model guidance is latching onto what could be our first shot at a strong winter storm, in the January 6-10 timeframe.

Tropical Tidbits

The above image shows 500mb geopotential height values in colored shadings, and MSLP values in contoured lines, across the West Pacific on New Years Eve. In this image, we see a strong low pressure crossing Japan, with a minimum central pressure value of 991 millibars, before sliding north and east towards the Aleutian Islands. If we apply the Typhoon Rule, which states that weather phenomena occurring in the West Pacific is reciprocated in the United States six to ten days later, we may extrapolate this to mean a strong storm could impact the US in a January 6-10 timeframe.

Other model guidance supports a weaker system moving over Japan, meaning we will need to monitor the region in coming days. If the storm crosses Japan at a weaker intensity, the storm here in the US would likely be weaker as well.

Purely for 'eye candy', here's the latest GFS projection of a storm in the East US on January 6th. This graphic isn't a forecast you should count on to verify.

COD

To summarize:

- A storm system may impact the US between January 6-10.
- Storm strength is still uncertain, and all aspects exhibit very high uncertainty at this juncture.

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

April 9-15 Multiple Potentially Significant Storm Systems

I'm seeing the threat arise for not one, but two potentially significant storm systems.

Tropical Tidbits

The GFS model has been consistently bringing in a strong upper level low into Japan around April 4th, beginning to attain a negative tilt on the image above, valid for the afternoon of April 4th (for more information on negatively-tilted storms, please click on this link to see the post published yesterday on this topic). 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. If we take the April 4th day and extrapolate it out 6-10 days, we arrive at the April 10-14 timeframe for what could be a hefty storm. I say it could be strong, as the strength of these East Asian systems has been reflected in the resultant United States storm . For instance, a strong storm over Japan does usually result in a strong storm in the US 6-10 days later, and that's what we're looking to see in this April 10-15 timeframe.

But we're not just looking for one system. This time, there are indications we could see two systems.

Tropical Tidbits

About a full day after the original system moves out from Japan, we see another swath of significantly below-normal heights enter Japan. The GFS image above, now valid for April 5th, reflects this, and we can see our first storm system that was discussed above now located just west of the ridge in the Bering Sea. This second storm system is kind of a tricky one. I'm watching closely here, as it could end up being one storm with residual cold weather just hanging behind. However, this forecast says we are in for two storm systems, and since we're entering spring, these strong storm systems can create nasty severe weather. For that reason, I'll err on the side of caution and highlight two storms in this post, but do realize that this may switch back to one significant storm.

The pattern I had highlighted earlier last week, which showed how the Northeast was at the most risk, is now a bit more hazy than when we last analyzed this timeframe. Model guidance is no longer as favorable for an East Coast impact, but rather than drop that region from a potential impact zone, I'll still tentatively keep the Central and East US in line for this storm. We should know much more about what this storm(s) could do in about 4 or 5 days from today.

As you can tell, there's a lot of uncertainty. Let's sum up what we do know.

- There is the potential for at least one significant storm system around the April 9-15 period.
- Severe weather does look to be a potential factor in this timeframe.
- Cooler and unsettled weather can be anticipated for this timeframe.

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 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

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 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

February 12-14 Potentially Significant Snowstorm

Model guidance is beginning to jump onboard the idea of a potentially significant snowstorm in the February 12-14 period.

We begin with the snowfall forecast from the CMC (Canadian) model. The CMC model goes all-out on this storm potential and throws down amounts over 12" in northern Georgia and a wide swath of North Carolina into Virginia, before laying down amounts near 24" in the Mid-Atlantic and New England regions as the storm bombs out to a minimum sea level pressure value of 961 millibars.

This is the CMC model forecast of 6 hour precipitation values and sea level pressure contours. We can clearly see the storm in all its might, dropping intense snows of nearly 4" per hour on coastal areas affected by the wintry side of this storm. The storm then deepens to 961 millibars 6 hours later as it pulls away from the East Coast. Taking the paralyzing snowstorm aspect out of this storm for a moment, the CMC would be printing out a potentially life-threatening event, due to the strength of this storm. We would be talking about severe wind damage, possibly catastrophic if this storm actually verifies. Luckily, I highly doubt we see a solution just like what the CMC here says. However, I do think we have to watch out for a storm in this time period.

This image above shows 500mb observed height anomalies on the left, and sea level pressure/high pressure-low pressure denotations/cloud cover denotations on the right. Both panels were valid on February 4th. If you've been with The Weather Centre for a while, you know how we use a rule created by Joe Renken that states a storm system in East Asia then results in a storm in the United States 6-10 days later. Looking at the panel above, we see that a strong storm system was observed cutting north across Japan on February 4th, as the deep blues in the left panel over Japan tell us. If we move ahead 6-10 days from that February 4th timeframe, we find ourselves with a potentially significant winter storm in the US in a time period of February 10-14. I have a good feeling this CMC model projection is indicating that this is the correlating storm. Since the Japan storm was strong, I have a feeling this storm in the US will be strong as well.

The CMC isn't the only model showing a big winter storm in this timeframe...

The ECMWF model also puts down significant snowfall from the Mid-Atlantic to the New England regions, though we see snowfall amounts reduced and moved a bit east compared to the CMC. The CMC model has always retained a bias of being too strong with storm systems, and it's more than likely that this bias is affecting its forecast at the top of this post as well. However, we still can take into consideration the idea that the CMC is printing out a general storm hitting the East Coast, and that idea is something the ECMWF agrees on. We see snowfall amounts of over 12" slamming northern Georgia and into the Carolinas, before a strip of 10-15" snow amounts strike coastal areas in the Northeast.

The ECMWF precipitation forecast at the storm's maximum impact shows the heaviest precipitation on the eastern flank of the storm system, with the system overall weaker than the CMC (which can be explained by the CMC's aforementioned bias), and cold sector precipitation (snow) much more scant (once again attributed to the CMC's bias).

The only model guidance system that isn't jumping on the idea of an East Coast snowstorm is the GFS.

The GFS model actually has the storm begin as two low pressure systems that eventually congeal into one system at the time this forecast graphic is valid (February 13). We can see that the majority of precipitation here is rain, which is located offshore, with snow hitting only coastal areas.

Snowfall amounts from the GFS model aren't even worth mentioning, with 2-4" accumulations only found near the coast.

So why is the GFS so different from the ECMWF?

When comparing normalized 500mb height anomalies from the 12z ECMWF and 12z GFS, both at forecast hour 96, it's not so much that the synoptic pattern is different, but more about how far south the storm pushes before it makes its jump up the coast. The GFS model on the left is noticeably weaker and further south with the storm in terms of these normalized 500mb anomalies when compared to the ECMWF, which has a stronger, slightly further north system. Another issue also appears to be how ridging is aligned downstream of the storm in the Atlantic. We see high pressure a bit suppressed in far eastern Canada, towards Nova Scotia in the GFS on the left, with the ridging more pronounced and stronger in the ECMWF forecast on the right. What's interesting is that the pattern upstream is in near-complete agreement among the models. We see a strong system over Alaska, with strong-yet-suppressed ridging across the Southwest US. Normally, this upstream agreement ought to result in agreement on the evolution of the storm, but in this case, it looks like it will be an issue of just how far south the storm goes. If we count the higher accuracy of the ECMWF and CMC models versus the GFS model as of late, as well as model guidance tendencies for the storm to track too far south and the ECMWF being rather consistent on this idea of an East Coast snowstorm, I think it's best to support the ECMWF/CMC solution in terms of track, NOT amounts. Amounts will be determined further in the future.

Andrew

Arctic Cold to Abruptly End in Mid February, Return in March

It's looking like we will see the recent Arctic cold come to a quick end in mid-February.

The image above shows the GFS Ensemble 500mb height anomaly forecast for February 17th over the western Pacific. We see strong ridging present over Japan and much of eastern Asia, with another swath of positive height anomalies displaced further east to the south of Alaska. Using the idea that a storm system in Japan can signal a storm in the US 6-10 days later, we can find that this strong ridge over Japan should also come back to haunt the US 6-10 days later. That would place warmer and quieter weather over the nation in the February 23-27 period. Considering high pressure should be affecting Japan both before and after this February 17th forecast graphic, it would be reasonable to think that this warmer/quieter weather may extend into early March, as well as closing out the last week or so of February.

This warm trend can be seen by the Earth System Research Laboratory's (ESRL) Analog Temperature 8-14 day outlook, as is shown below:

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As we move into early March, it looks as though we will be heading into new phases of the Madden Julian Oscillation (MJO). Looking at the March 8th MJO OLR anomaly forecast, in the middle panel of the left side of the images above, we see deep blues spread out across the waters to the southwest and southeast of India. These deep blues represent enhanced tropical convection, and it also means an active phase of the MJO will be evolving.

If we compare that March 8th forecast image to the MJO OLR Composite image from the Australian Bureau of Meteorology, we see that the blues on the forecast image line up the best with MJO Phase 2 and MJO Phase 3, which are seen as the second and third images down from the left-hand side of the panels above. If we look at the low amplitude Phase 2 MJO (which guidance predicts we see when the MJO does enter Phase 2 before transitioning to Phase 3) 500mb height anomaly image below from scotlandwx.co.uk , we find that deep negative height anomalies are favored over the East US, resulting in colder than normal weather. The troughing in the Gulf of Alaska remains present, with suppressed ridging over the north central Pacific Ocean. Long range ensembles favor this type of set-up for the middle-late portions of February, and it's very possible this continues into March. To clarify, while the set-ups may be similar from mid-February onward, I currently only expect warmer weather for the mid-late parts of February due to East Asian ridging. Beyond that period, into early March, indications of East Asian ridging dissipate, allowing cold weather prospects for early March to flourish.

Low amplitude Phase 2 MJO 500mb height anomaly composite

The 500mb height anomaly composite for all amplitudes of a Phase 3 MJO also favors some cooler weather in the East US, though the cold is more restricted to northern parts of the nation.

So, let's sum it all up.

•We are looking at warmer weather over the United States in the closing week of February, possibly extending into the opening days of March.

•The pattern after the early-early March warm-up looks chillier, with a potentially favorable MJO (keyword is potentially due to the typical long range forecast caveats and inaccuracies) and favorable signs from East Asia after ridging moves out.

Andrew

February 13-15 Potential Snowstorm

It looks like we may see a winter storm along the East Coast in the February 13-15 timeframe.

The GFS model indicates we will see a negatively tilted trough work its way down into the Northeast and Mid-Atlantic around Valentine's Day, in the midst of an established northwest flow regime. We see this regime set up as a result of storminess over the Gulf of Alaska, and a suppressed ridge in the West US.

The GFS model wants to take what appears to be a strong clipper system eastward into the Northeast in association with the trough we saw in the image above. The clipper then transfers to the coast on the morning of Valentine's Day, resulting in snowfall for the interior Northeast. Rain looks to be the preferred precipitation type on this model solution for coastal regions. Since this is still in the long range GFS, none of this should be taken verbatim- we're trying to pick out the general pattern that could then yield a winter storm. In this case, the northwest flow with an Alberta Clipper transferring offshore seems like a rather likely scenario if the opportunity arises for a clipper to form around Valentine's Day.

The ECMWF has a similar situation, with the 500mb height anomaly forecast highly indicative of the northwest flow regime we discussed. The suppressed ridge and storminess over the Bering Sea is clearly evident, though the ridge in the Southwest is so suppressed the flow is borderline-zonal in that area. Nonetheless, we can still see the northwest flow alignment across the contiguous United States (CONUS).

The ECMWF model has the storm system impacting the Mid-Atlantic primarily, before heading off out to sea, only scraping coastal portions of the Northeast. This solution would lay down snowfall in the Mid-Atlantic states of North Carolina, South Carolina, West Virginia, and Virginia. This particular ECMWF model forecast lays down over 13" of snow in these areas, but these amounts would be better off cut in half for more accurate (but still slightly overdone) amounts.

So why will this storm hit the Mid-Atlantic and Northeast?

The answer lies in the jet stream and 500mb level. Here in the jet stream, we see the storm system well defined in the Central US on the 12th of February. If we look closely at the winds surrounding the jet stream, we see a jet streak (area of higher winds within the jet stream) positioned to the right of the trough. Typically, when a jet streak is to the right of the trough, the trough will lift north. This same principle applies here, as we then see the trough lift north and east, tilting negative as it does so to indicate the storm has reached maturity.

The 500mb level, shown two images above this jet stream graphic, also supports the storm lifting northward. We see a strong ridge of high pressure located well offshore of the East Coast of the US, which would nearly assure the storm lifting northward. Additionally, the trough beginning to tilt negatively in the East US would help out with the storm wanting to move north.

So what can we establish right now?

-The synoptic pattern looks favorable for a winter weather event in the East Coast, thanks to an evolving northwest flow pattern.

-A potential storm system is being modeled on forecast guidance that may impact the East Coast of the US.

-If a storm system does form in the United States, it looks like it will be favored to bring snow to inland portions of the East Coast, rather than coastal regions.

Andrew

January 24-28 Potential Apps Runner / Nor'easter Winter Storm

There is the potential for an "Apps Runner" or Nor'easter winter storm around January 24-28, as a storm begins to traverse the Bering Sea in a favorable position.

This is the ECMWF 500 millibar anomaly forecast for the afternoon of January 5th, the day this post was published. You can see the deep negative geopotential height anomalies over the southwestern portion of the Bering Sea, and I drew a line outlining a rough track of where this storm system is projected to go in the next few days. Around January 6, the storm begins to cut north across the central/eastern Aleutian Islands, and then turns a little northwest to swirl in the Bering Sea. This is a telltale sign that we may be in for an Apps Runner or Nor'easter winter storm, as Joe Renken's Bering Sea Rule describes.

The Bering Sea Rule states that by watching storm systems make their way across the Bering Sea, one can identify where and when a storm system will show up in the United States. The general timeframe is 17-21 days after a storm appears in the Bering Sea, a storm will appear in the United States. This rule is already in use with the January 17-21 potential Colorado Low, and now it looks like the Eastern US might encounter some stormy weather if the Bering Sea Rule verifies correctly (which it has, when used previously).

The storm in the Bering Sea skirts in the southern portion of the waters across the January 5-6 time period, before cutting north on the January 6-7 time period. If we extrapolate that time frame 17-21 days out to use the Bering Sea Rule, we end up with roughly a January 24-28 period that we should watch for a potential winter storm. The reason I am labeling it as a possible Apps Runner or Nor'easter is because of how far east it cuts north. Joe Renken indicates that the further west storms cut north in the Bering Sea, the further west they end up 17-21 days later in the United States. In this case, our storm system here cuts far enough east that an Apps Runner or Nor'easter scenario does seem viable. The Bering Sea system is also displaying traditional characteristics of a Nor'easter scenario, where the storm moves in the southern waters of the Sea before cutting north quickly. A Nor'easter forms in a similar fashion, where the energy traverses the Southern US before shooting north along the East Coast.

To sum up:
There is potential for a winter storm over the January 24-28 time period, and indications are it could affect the Ohio Valley via an Apps Runner, or the Eastern Seaboard by way of a Nor'easter storm system.

Andrew

November 25-27 Nor'easter Final Update

Mid-level vorticity analysis reveals that the two pieces of energy that will combine to form the Nor'easter are currently moving in their projected directions, and should merge in just a handful of hours.

It is expected that the rather strong piece of energy in Texas will shift eastward, as that system in Canada drops to the southeast. As we go through the next day or two, the two pieces of energy will merge and shift northeast to provoke a heavy rain event and substantial snow event over parts of the Northeast and Mid-Atlantic.

Snowfall forecasts over the next 60 hours have totals either flirting with or above the 12 inch mark along western New York, west Pennsylvania and northeast Ohio. Lighter amounts are anticipated in the higher elevations in the New England area, but will still allow for plowable amounts. Lower elevation areas should receive a couple of inches from this system, while coastal areas will receive some major rain amounts.

Rain amounts along the coast should push above 2 inches, making this system quite a wet one. I find it possible that some areas will experience flooding, though I'm not sold on a huge flooding event. The more likely scenario is rather heavy rain for most of the Eastern Seaboard in the Northeast and Mid-Atlantic, with lighter amounts inland. Bear in mind that while this forecast shows significant precipitation for the inland areas in line for snow, it's likely that the snow will be heavy, as this is only November, thus light, fluffy snow is rather unlikely.

Stay tuned to your local weather service if you are at risk of this winter weather. Winter storm watches (navy blue), advisories (purple) and warnings (pink) have already been hoisted across the Northeast and Mid-Atlantic as this first snow event begins to unfold.

Andrew

January 24-27 Winter Storm

NOTE: Midwestern/Ohio Valley cities could see flurries, little to no accumulation expected.

An accumulating snow event will occur in the Mid-Atlantic in coming days.

It appears that two pieces of energy will combine in the Mid-Atlantic, a byproduct of a clipper system coming from Canada and another piece of energy from the Plains. These two will combine offshore (or very close to the ocean) and produce an accumulating snowfall across the region. Amounts are expected to be on the lighter side, with a trace to 2 inches expected across Pennsylvania, Maryland and eastern Kentucky, to name a few states. Ohio may also get in on the snowfall. Two to four inches could fall in West Virginia and Virginia as a result of this disturbance. Again, nothing major, but enough to bring out the snow plows and shovels to do some clearing.

Andrew

January 29-31 Potential Winter Storm

Images courtesy of TropicalTidbits

The models are hinting at the evolution of a potentially major storm system that would affect much of the central and eastern US.

Above are two forecast images from TropicalTidbits, showing the forecasted sea level pressure and precipitation in mm/hour. The top image is valid on the morning hours of January 30th, with the bottom image valid the evening of January 30th. The synopsis involves a storm system cutting along the the Midwest from the Plains and into the Ohio Valley and eventually the Northeast. Throughout this process, strengthening appears to be the key word of this system, as it eventually drops to 982 millibars off the coast of New England. If you look really closely, you can make out a blue dashed line with the number '540' on the line. This is the rain snow line; any precipitation north of the line is snow, and any precipitation south is rain. Using that as our guide, the GFS calls for possibly upwards of 1 foot of snow in parts of the Midwest, with possibly amounts nearing 10 inches in portions of the Northeast. If only this were a trustful forecast. Alas, beyond 5 days out the GFS model is biased towards making storms too strong and temperatures too cold, giving many the long range forecast of over a foot of snow, only to find rain and warmer temperatures when the forecast verifies- and that's even if the storm happens!

Either way, I will provide updates on this storm as the date draws closer, but for now, don't get too hung up on the forecast.

Andrew

January 24-26 Potential Winter Storm

I am monitoring the threat for accumulating snow from January 24th to January 26th.

The GFS and ECMWF models are now hinting at a strong storm system crossing from the Central Plains east into the Midwest or Great Lakes. At the moment, there is a difference between the two, with the American GFS model taking the system into Chicago and the European ECMWF model taking the system into the US/Canada border in the Western Great Lakes. The map I drew above went by the GFS model for the sole purpose of covering all possibilities as far as who has at least a chance of getting snow at the moment. If this storm does happen and the models are correct, I would expect a good accumulation event occurring in the North Plains and Upper Midwest, possibly in the Great Lakes. The GFS model shows a fair accumulation event above 4 inches for some people in the Northeast, so that threat will need to be monitored.

Andrew