Sunday, March 31, 2013

April 5-7 Potential Winter Storm - Midwest, Plains

The potential exists for a winter storm to impact the Plains and Midwest between April 5th and 7th.

The GFS American model has a winter storm moving through the Plains and Midwest beginning on April 5th and continuing through April 7th. Current indications are that this system will drop from Canada and progress through the northern Plains and Upper Midwest. As the system takes this path, a snowstorm will likely evolve as cold air produced from the abundant snow cover in Canada and continued high pressure presence over the Arctic.

Model guidance suggests snowfall amounts from this system would well exceed half a foot, and many locations would top one foot of snow. The heaviest amounts would be found in west central Wisconsin, central Minnesota, northeast South Dakota and extreme southeast North Dakota. Lesser amounts would be found away from the aforementioned areas, but a sharp cutoff will likely exist south of those areas.

Now, the European model does not believe this will be a winter weather event. The model indicates a rain solution is the more likely scenario, and snow would not be nearly as abundant as the American model indicates. A few notes concerning the models, for those trying to pick out which solution is more likely for themselves: The American model has had recent success with storm systems over the European model. Models do not handle springtime storms well due to the unstable temperature profiles (in the sense that precip. types are more uncertain than in the winter).

I will not pick out a solution right now as too much uncertainty exists for my liking, but this storm does need to be monitored for the possibility of a late-season snowstorm.


Long Range Chatter - March 30, 2013

Temperature anomalies from the last week show the lack of spring continuing throughout nearly every region of the nation, save the Southwest. Temperature anomalies, shown in Kelvin, dropped as low as 10 degrees below normal in the Dakotas, with even the Gulf of Mexico experiencing some of this cool weather. This cold weather has been provoked by prominent high pressure over the Arctic Circle and Greenland, as this reanalysis image from March 25th shows:

500mb height anomalies are placed on the left, where warm colors depict high pressure
and cool colors indicate low pressure. Mean sea level pressure contour lines, as well as cloud
cover are shown on the right half of the image.
In response to this extreme high pressure over the Arctic and Greenland, low pressure has been provoked to develop over the central and eastern US, more-so over the latter region. As long as we see that high pressure area over the upper latitudes, chances are more than likely that the tendency for cooler weather will continue to fall upon the central and eastern US. With the cold weather, we also expect a tendency for low pressure in very similar regions, so storm systems moving into the eastern US could be more commonplace than instances of above-normal temperatures.

European ensembles predict that this high pressure will remain stagnant over the Arctic and Greenland from now until at least 10 days away. Consequential low pressure will also stay in place north of the Canadian Maritimes and into eastern Canada. New England will also be affected by this relatively stagnant body of low pressure, and these effects may range from below normal temperatures to unusually cloudy days (both of which I consider likely). High pressure attempting to develop over the Western US will enhance cold weather potential south of Canada, possibly encompassing millions east of the Mississippi.

European model temperature anomalies 5000 feet above ground display this cold weather trend, clearer than day in the Northeast. Below normal temperature anomalies resonate well into Canada, sideswiping the Great Lakes and Upper Midwest. Warmer than normal temperatures will assist the skiing season in coming to a close in regions where resorts remain open. This forecast, valid for forecast days 6-10, is pretty likely to turn out when you look at what has been experienced and comparing it to what is being forecast. High pressure will remain favorably positioned over the Arctic to allow cold weather to hit regions of the US previously hit by the cold, and also spread eastward.

Next 10 days look to remain below normal in temperatures for the central and eastern regions of the United States. Warmer than normal temperatures should persist in the Western US. I feel that best chances for storm systems will be in the northern Gulf Coast (TN/AL/MS/GA) and north, along the Eastern Seaboard and into the New England area. Probably will not see any significant Nor'easters in this timeframe, although a wayward storm system well offshore may allow coastal cities to get a quick bout of precipitation.


April 5-6 Potential Coastal Wintry Storm

Model guidance remains iffy on the prospect of a potentially wintry storm system between April 5-6 in New England.

Discussion: Previous model guidance indicated this storm would be a mostly rain event, but new model guidance has this storm system producing wintry precipitation in southern Maine and a few other coastal states in the wake of this system. The American model, pictured above, has the system stay in above-freezing temperature territory for the heavy majority of its lifespan, hitting coastal towns with a rain event. As is the case with springtime storms, temperatures are much more marginal with this storm than typical winter storms. There is potential that there will be no snow from this system and it could be all rain. Logical forecast to go with right now is a rain event with weak backend snowfall. Heaviest snowfall (if any) would affect Maine, the state furthest north and thus furthest into the colder temperatures. Light lake effect precipitation is likely to commence when the storm moves off, but as winter draws to a close, we find the potential for massive lake effect snow events rapidly decreasing. American model has snowfall amounts staying at or below 2 inches for select coastal areas, whose locations are to be determined.


Saturday, March 30, 2013

April 10-12 Potential Storm

American GFS model MSLP anomaly forecast for 10 days

European ECMWF model 500mb anomaly forecast for 10 days
Medium-range model guidance is in unusually good agreement on a storm system digging into the Southwest US as a closed low before making its way east and affecting areas east of the Front Range. Below normal anomalies for the model's respective fields shown above depict the storm system, while the warmer colors in both images indicate high pressure. European model is considerably further north with this storm system over the American GFS. Because the European model only forecasts out to 10 days, we cannot see how far in the future the European takes it. However, the American model DOES go through the full timeframe of this storm, and we will examine its forecast a little later on.

General atmospheric flow in both images is highly meridional, and the lack of a positive tilt (highest vorticity pointing towards the southwest) means that this system should quickly occlude and shoot north into the Plains towards Canada. When this occlusion happens, an accompanying cold front is likely to begin forcing the massive high pressure system out. Based on temperature forecasts from American model and European ensemble system, temperatures surpassing 60 would be common in and south of the Great Lakes. This could set the stage for a severe weather event. European model itself has cities like Chicago and Des Moines flirting with the upper 70's as the high pressure system takes over as illustrated in the above images, while the American model has those cities closer to the 60's.

Precipitation forecast on April 12th suggests the suspicions of a severe weather event may verify, as a heavy precipitation event looks to impact the southern Plains, likely encompassing stronger storms in the typical cold front's linear storm formation. Time will tell if this linear formation ends up being a squall line or just pockets of heavy rain. Lighter amounts also exist further to the north, stretching as far north as far northern Wisconsin. Examination of severe weather parameters for this timeframe reveal rather high deep level shear conducive for at least marginally strong thunderstorms. Lack of widespread instability across southern Plains is something to watch, although elevated instability immediately onshore of the Gulf Coast would allow for some solidly strong thunderstorms to thrive.


April 5-6 Potential Storm

There is potential for a coastal storm in the Northeast from April 5-6.

Fresh model data indicates a storm system will form in the Southeast and manifest itself to move northeast, just offshore of New England. The system will not be close enough to provide an opportunity for snow, and the presence of warm air along coastal cities means any snow potential will be dashed there by a chilly rain. Lake effect snowfall may be possible in western New York, but this looks to be a rather marginal opportunity for any accumulating snow. Best chances for accumulation reside in western New York as a result of the lake effect snow, and those accumulations may be very light. There remains time for this situation to change, but right now I'm seeing a non-event as far as snowstorm potential goes.


Summer Warmth On The Way

The latest run of a member of the European ensemble set has summertime warmth flooding the nation just 10 days from now.

The image above is from the European ensemble control run, which is a member of the ensemble set that has its parameters unchanged. As you may recall, ensemble members are forecasts from the model itself, but their starting parameters are slightly changed in one way or another. The control run does not have its parameters changed. This forecast, valid for the evening of April 8th, has a massive warm-up across much of the nation, with every state east of the Colorado Front Range (except a few select New England states) reaching full-on spring or summertime warmth.

Cities like Houston, Orlando and Atlanta would have temperatures very similar to those in Chicago, St. Louis and Detroit. The massive warm-up would not reach northern ND, MN, WI or the Upper Peninsula of Michigan, although a forecast 240 hours out is not nearly written in stone.

The unusually warm temperatures following this unusually cold start to spring would most likely be a byproduct of an intense ridge of high pressure sitting across the Great Lakes, Midwest and Plains. Latest indications are that this warmth would be wiped out a few days later as the storm system you see in the Southwest moves on through the nation, but the incredible expanse of the high pressure system means the warmth would not go down without a fight. Time will most certainly tell if this warmth comes to fruition, but this forecast certainly warms the heart of those frowning upon the cool and snowy start to spring.


Wednesday, March 27, 2013

April 5-7 Potential Nor'easter

The American GFS model is showing a strong storm in the Southeast US on April 5th, in an event that could pose the next threat for a Nor'easter.

The 9 day forecast image of precipitation and mean sea level pressure above has a strong storm system sitting on the Florida/Georgia border. This system is producing widespread and intense precipitation on all sides of the system. The chart indicates its mean sea level pressure is still above 1000 millibars, and while the Gulf of Mexico will be wide open to this system for widespread precipitation, I find it hard to believe that this precipitation will end up as heavy as it is being predicted. The long range American model always has troubles with strength and extent of precipitation in a storm system, and this one is no exception.

Now, the American model proceeds to take this storm out to sea after moving through the Southeast. However, I think there is potential for a Nor'easter to take place rather than the system just moving offshore. Shown above is a forecast chart for 500 millibar anomalies, where warm colors indicate high pressure and cool colors show low pressure. Our storm system is very visible along the Gulf Coast, and it looks like it should go up the coast. However, for some unknown reason, the American model refuses to do so. Considering high pressure over Greenland is strongest to the immediate west of the nation, this storm should have very strong backing to go up the East Coast, possibly producing a strong rain or snow event for many. But neither the American or European models allow this. Based on personal experience, we are almost guaranteed to see this storm's track change, possibly to a position more favorable for sliding up the Eastern Seaboard. There remains a lot to be discovered, but I do believe the potential is there for a Nor'easter.


2013 Preliminary Atlantic Hurricane Outlook

Hello everyone, and welcome to The Weather Centre's Preliminary Atlantic Hurricane Outlook. In this outlook, because it is just the preliminary outlook, we will only examine my current analog package and a batch of ENSO model forecasts.

We start now with the analog package. I utilized the Pacific-Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) for this outlook's analog years. The PDO involves a positive and negative phase, where each phase depends on the prominent water temperature anomaly in the Northeast Pacific. A glance at the sea surface temperature chart for the northeast Pacific reveals a swath of above normal water temperatures in the offshore regions of the Gulf of Alaska, with below normal temperatures immediately offshore of North America and Alaska. This is the typical signature of the negative PDO. As for the Atlantic Multidecadal Oscillation, we also see a positive and negative phase with this index. The positive AMO signifies warmer than normal water temperatures across the waters off Greenland and in the far north Atlantic Ocean. In the same sense, the negative AMO allows below normal water temperatures to encompass the North Atlantic waters.

After choosing specific years from these two indices, I combined my chosen years and used the ones that had both the PDO and AMO in phases similar to what we are currently anticipating. As a result, I came up with the years 1951, 1952, 1955, 1956, 1999, 2000, 2008, and 2011. All of these years had a clear negative Pacific-Decadal Oscillation and positive Atlantic Multidecadal Oscillation, which is what we are experiencing now and what we should experience moving forward into the spring and summer months.

Let's take a look at an archive of hurricane tracks during the aforementioned years to see if we can see a trend in my analog years that could assist in helping us find a common track for the upcoming season.

In 1951, we saw a storm season that had many storms going out to sea rather than towards the US Mainland. At least 3 of those storms didn't even have a chance of making it to the United States. However, there were a few storms that did have a close brush with the Carolinas, as well as one landfall in Florida. A couple storms did make a threatening track towards the Gulf, but for one reason or another they did not hit the US. One storm (Hurricane Charlie) did hit Mexico, the Yucatan Peninsula, and Jamacia. All in all, the trend for this year was a slight Gulf threat with multiple close calls on the East Coast.

1952 was not unlike 1951 in terms of where tropical systems went. While the Gulf of Mexico was considerably quieter with no systems actually in the heart of the Gulf, there was one landfallig system in the Southeast US, another landfall in Florida, and at least 3 storms that ended up recurving out to sea. The system that struck Florida, which formed on Groundhog Day (yes, in February), was never named. Hurricane Able was the system that hit the Southeast. The trend in this season was a threat to the East Coast and a rather quiet Gulf of Mexico.

1955's Atlantic Hurricane season involved a pretty darn active season in terms of landfalling tropical systems. We saw multiple impacts on the Gulf Coast, especially in Louisiana and Mississippi. We also saw possibly more than 2 separate landfalls on the East Coast, all of which struck the Mid-Atlantic (one also sideswiped the Northeast). Tropical Storm Brenda was one of the systems that hit the Gulf Coast, and it was Hurricane Connie that slammed into the East Coast. Tropical Storm Five followed Brenda into the Gulf, while Hurricane Diane took a hint from Connie and sped towards the East Coast to make landfall. The clear trend here is an active landfalling season in the Gulf and East Coast.

1956 continued the idea of storms running dangerously close to the US Mainland, even making landfall a couple points along the way. We saw a rather unusual season in that the majority of the storms took almost a due-north path out to sea. Usually, storms will form off the coast of Africa and curve west before doing a 180 and going out to sea. In this season, the storms just formed and made their intentions clear as day. Tropical Storm One, the first named system of the season, impacted the Gulf with a landfall. Both Hurricane Anna and Tropical Storm Dora hit Mexico, while Hurricane Flossy did a double-take by hitting the Yucatan Peninsula and the Gulf Coast. An unnamed subtropical cyclone hit Florida and skirted into the Mid-Atlantic. The trend in this season is clear: Tropical cyclone threats were highest in the East Coast and Gulf Coast.

1999 was no different than previous years. We saw multiple tropical cyclones skirt immediately offshore of the Eastern Seaboard, and the Gulf of Mexico came under fire. We saw extreme southern Texas take a landfall from Hurricane Bret, while Florida was surrounded by several near-misses and at least two landfalling systems. It was Hurricane Dennis that took one of the most awkward tracks I have ever seen a tropical cyclone take. It began to curve out to sea after narrowly missing eastern Florida, but suddenly make a hard turn south, then a hard turn west before making landfall in the Mid-Atlantic as a weak tropical cyclone. The trend continues; East Coast and Gulf Coast were threatened in this season.

The year 2000 was a bit different in that the number of threats to the East Coast was reduced. We saw more of a tendency for storms to curve out to sea earlier than storms in, say, 1999. The state of Florida did bear the brunt of at least one landfall (courtesy of Hurricane Gordon), while Alabama and Georgia were affected by a tropical cyclone known as Tropical Storm Helene. A tropical depression also made landfall in the western Gulf Coast, although it is not shown in the map above. The Gulf Coast definitely made headlines as the most affected area this season, with the East Coast in a not-so-close second.

2008 brought an absolutely chaotic Atlantic hurricane season. We saw over half a dozen tropical cyclones hit the Gulf Coast, with one cyclone hitting the East Coast. Tropical Storm Cristobal affected the East Coast, while Hurricane Dolly and Tropical Storm Edouard hit the Gulf Coast. Tropical Storm Fay zig-zagged through Florida, while Hurricane Gustav ravaged the Gulf. Hurricane Hanna hit the Eastern Seaboard, and it was Hurricane Ike that dominated the Texas coast. The trend is probably the clearest we have seen in all of the analog years: The Gulf experienced the largest threat, with the East Coast also getting in the action.

My last analog year, 2011, echoed previous analog years, but also raised the recurring theme of storms curving out to sea. We saw the heavy majority of tropical cyclones curving out to sea in 2011, with little to no damage coming between them. However, there were two Gulf Coast landfalls that were weak, as well as one Mid-Atlantic landfall. The final analog year continued the idea that the US mainland was threatened.

The next piece of evidence I want to show you is a chart of the latest observed sea surface temperature anomalies over the Atlantic Ocean. I outlined three regions of anomalies- an above-normal sea surface temperature (SST) area in and just south of Greenland, a below normal SST area to the east-northeast of the Mid-Atlantic coastline, and a large swath of above normal SST values from the coast of Africa and west into the Caribbean. This type of arrangement of SST anomalies is called an Atlantic Tripole. Years that had an Atlantic Tripole in place had a positive correlation with the monthly hurricane total from June to July and Accumulated Cyclone Energy (ACE) values. This positive correlation means that, since the Atlantic Tripole is in its positive phase right now, we could reasonably expect more tropical cyclones than normal to form this season, and those cyclones could have more energy than normal, which would then raise the ACE index.

I am monitoring the El Nino-Southern Oscillation at this time, and current sea surface temperatures suggest we are in an El Nino. I don't really want to touch on that subject, as model forecasts have the Nino fighting an uphill battle as far as being able to survive during the hurricane season. Until the model forecasts clear up, I don't have enough confidence to lean one way or another on the presence or lack of an El Nino.

Based on my current analog package, combined with the Atlantic Tripole and a few other factors that greatly contribute to the Atlantic hurricane season, I believe that the threat to the Gulf Coast is 'High'. The 'High' threat means that the risk of a tropical cyclone of ANY strength hitting the Gulf Coast is pretty significant. I cannot go in-depth into strength of the cyclone until my official outlook (which will be out in Late April or Early May), but I cannot rule out the potential of a hurricane hitting the Gulf. As for the threat to the East Coast, I have classified the threat as 'Medium-High', meaning that there is a pretty decent chance of a tropical cyclone of any strength affecting the East Coast. Based on the analog package, the threat of a tropical system hitting that region is pretty solid.

If you have any general questions (no specific timing, strength or location questions, please), don't hesitate to ask. I will try my best to get back to you ASAP.


Tuesday, March 26, 2013

Late April Snow Potential Means Winter Not Done Yet

WARNING: The chances of this actually happening are essentially zero. DO NOT take this as an actual forecast. Take it as the smallest grain of salt known to man.

The long range CFS model is projecting an increase in snow depth across the Ohio Valley and Northeast in 2 of the 4 CFS ensemble forecast members. All of the ensemble members have an increase in snow depth across a portion of the northern US. While usually the agreement of all of the ensemble members of snow in some portion of the North US is encouraging to the validity of the forecast, I have a hard time believing that there will be a snow event in late April.

For one, the increased intensity of the sun greatly discourages snowfall potential. For another, the Northern Hemisphere's climate is naturally changing over to a springtime ''feeling'', with warmer temperatures covering a greater portion of the nature, and an increasing warm sector to the east of storm systems. However, with continuing chances for an unusually weak polar vortex, cold air will be relatively easier to come by, especially in the Northeast. To up the ante, an unusually active Pacific jet stream could draw in more cold air to the south, increasing chances for snow.

Again, this is almost certainly not going to verify, but the fact that the chance is even being suggested is a testament that this winter is unlikely to go quietly.


Sunspots Well Below Forecasted Numbers

It has come to my attention that the number of sunspots is well below forecasted values for this time of year. Shown above is a graphic from NASA, showing two different sunspot forecasts. If we use the small ticks on the (think back to middle school math here) y-axis, we find the 2010 mark predicts up to ~175 sunspots at this time. It is worth noting that these forecasts appeared on an article published in 2006. Regardless, both forecasts were showing very high numbers for the decade of 2010-2020.

Now shown above is an image of the last four solar cycles- Cycles 21, 22 and 23 are shown in blue, black and red respectively, while the in-progress Cycle 24 is shown in purple. If we look at the most recent observation of the sunspot number, we find that the number of sunspots currently stands at roughly 60- and we're at the height of the sunspot cycle! This means that the forecasts above were off by a minimum of 100 sunspots- a huge difference that shows just how weak the sun is, and raises questions about what its effects could be in the near future.

Short term, nothing major looks to be happening. Incredibly small temperature decreases in comparison to previous years are possible, and a decline in the number of solar flares and coronal mass ejections is probable. Long term, things get more interesting. If the sun does what I expect it to do, we are likely to see a multi-decade decline in temperatures across the world. We must remember that the sun has been recognized as the main driver of climate change, so the decrease in the number of sunspots (and thus the strength of the sun) should allow for at least a slight cooling trend in the world. I'm not willing to discuss global warming in this post, this is just pointing out how the forecasts for sunspots are off compared to what is being observed.


30-Day Sunspot Cycle in Turmoil

The 30 Day sunspot cycle that can help determine a variety of mesoscale factors has been sent into turmoil over the past month.

In the attached image, you can see how the sunspot cycle was fairly regular over the last several months. However, as of late, the cycle has essentially shut down and has been in the minimum of the cycle for the past month or more. The unusual quietness of the sun could help explain why the cold seems more prolonged and spread out. It also may assist in showing why there has not been persistent low pressure in the West US, as the 30 day sunspot cycle and Pacific-North American index have a negative correlation with one another.

Potential implications in the near future include continued instances of slightly prolonged and slightly stronger cold weather across the nation than what it would be if the cycle was at its regular. Other impacts include less pressure on the Central and East US to produce dominant high pressure. Rather, they would be more inclined to keep low pressure/general cool weather in the aforementioned areas.

If the cycle does not get out of its unusual antics in the next month or two, we could be looking at some solid impacts on spring, including the potential for increased instances of cold weather and slightly increased stormy patterns.


2013 Preliminary Atlantic Hurricane Season Outlook Release Date

The 2013 Preliminary Atlantic Hurricane Season Outlook will be released WEDNESDAY, MARCH 27 at 12:00 PM Central time.

Monday, March 25, 2013

April 5-7 Potential Storm

There is potential for a major storm system hitting much of the nation between April 5-7.

The latest American model forecast has a major storm system impacting the Midwest, Great Lakes and South US. As of now, the latest American GFS model has a solid snowstorm hitting southeast Minnesota, portions of Wisconsin, portions of Iowa and even into southeast Nebraska. This would be 'heart-attack snow' event, in that the snow would be very heavy due to marginal temperatures. As of now, the European model does not have this timeframe within its forecast period- we will need a few more days before that model can grasp the April 5-7 time period and confirm or deny this potential storm system.

Current thinking on this system is that there is potential- the long range looks to have an active Pacific jet stream, something that could enhance storm chances and storm strength if the storm were to happen.


April 2-4 Potential Storm

There is potential for a winter storm from April 2-4.

The long range American model is projecting a strong storm system to hit the Midwest between April 2 and 4, bringing significant precipitation to the Plains, Midwest, Great Lakes and South US. The American GFS model has been projecting this storm system to hit the nation for at least a few model runs, although the strength and expanse of the precipitation varied. Taking a preliminary analysis at this forecast map, it looks more like Nebraska and southern South Dakota could achieve a significant RAINstorm (bet you thought I would say snowstorm, right?), while southern Minnesota and maybe into Wisconsin could reach the needed criteria for a big rain event. Towards the South, it seems more apparent that this would also be a rain event, possibly even a severe weather event. However, the exact dynamics in this event are very much to-be-determined. Current wind shearing forecasts during this timeframe are optimistic for at least a few stronger thunderstorms, but nothing reaching the level of intense severe weather event.

The European model is actually showing an incredibly similar situation for this event, putting the center of low pressure in what appears to be the exact same spot as the American model. The European model has this storm system just a touch weaker than the American, but the fact that their placement of the storm system matches up as well as it is is incredible enough.

The American ensemble forecasting system has the system much further to the south than these two model forecasts, and both ideas will have to be monitored in the event that this system's potential does come to fruition.


Long Range Chatter; Will The Cold Ever End?

It’s looking more and more like the unusually cold weather we have been experiencing may very well continue through the remainder of March and at least a week into April.

Much of the country has been in the grip of a serious chilly start to winter, with temperature anomalies well below normal in many parts of the country. We have seen lower than 6 degrees (K) below normal in the heart of the Plains, with only a fraction of the Southwest and much of New England getting into above normal temperature anomalies from the start of March to March 23rd. While this may seem like a brutal start to spring, there's only slight indication it could end by mid April.

Shown above is a forecasted image from the European ensemble system, projecting 850 millibar temperature anomalies for 12 days from today. While a brief relaxation of the current cold snap is incoming, the chances of a follow-up Arctic cold shot are high. The European ensembles have anomalies just above 10 degrees (C) below normal across much of the northern Plains and Upper Midwest, with less-intense below normal anomalies across the Midwest and the rest of the Plains. Cool weather could reach as far as New England. This would more than likely continue the streak of cold weather across the nation, and the European ensembles bring another cold blast into the same regions just under 2 weeks out.

In the longer range, the American ensemble mean pushes the below normal temperature anomalies out of the Contiguous United States on March 31st. However, just a day later, we see a progressive cold shot in the Upper Midwest, and these progressive cold shots continue throughout the 16 day forecast period. In the longer range, the American ensembles seem to be hinting at below normal temperatures, mainly centered in the Eastern Seaboard and parts of the Northeast.

The general idea of the longer range is high pressure will continue to hold its ground over Greenland. When you see the placement of high pressure over Greenland, it is common to see an increased risk of cold weather across the northern Plains and New England. It also looks like we will be seeing a more active Pacific Jet Stream in the longer range, something that could add energy to the storm potential (winter weather and severe weather), especially in the Northeast. There are a few more indices I am observing that seem to support some stormy times for the Northeast. Whether that ends up as winter weather or severe weather remains yet to be seen.

So what is driving all of this cold weather??

This past winter, I continued to press the issue of how snow cover over Siberia in October could affect temperature anomalies in the following winter. In October 2012, we saw below normal snow cover for the first half of the month. This reflected nicely with December 2012 temperature anomalies, as shown below:

December 2012 brought above normal temperatures to the Plains, Midwest and Great Lakes, among other regions. New England ended up with below normal temperatures, as did the southern half of the Eastern Seaboard. California and portions of Nevada also got in on these below normal temperatures. I feel very strongly that this was indeed the Siberian snow cover correlation at work.

Looking towards mid October, we see a moderation in snow cover anomalies over the northern Hemisphere. Let's take a look at what January 2013 brought, temperature anomaly-wise.

As unequal as this may look, you can kind of see how the Plains cold and Northeast warmth can cancel out. Now, this could very well go towards the side of below normal temperature anomalies across the month of January, but I still can see how the relatively normal snow cover anomalies during mid October 2012 can reflect onto the observed temperatures in January.

Now, the end of October 2012 held very above normal snow cover. This correlates to a weaker than normal polar vortex, which can easily translate into below normal temperatures across the nation. Considering the snow cover anomalies came in late October, and we are seeing the extreme cold now in March, there is little reason to not believe that the Siberian snow cover/temperature correlation isn't an actual index.

Beyond the beginning of April, I expect a rather moderated temperature pattern, but with cold shots moving throughout the nation every once and a while. The frequency of these cold shots will decrease as spring progresses on and winter inevitably releases its grip on the nation that should be enjoying a beautiful spring.


Saturday, March 23, 2013

April Fool's Day 2013 Potential Winter Storm

Long range model forecasts are calling for a major storm system in the April Fool's Day timeframe.

As much as a caveat a storm on April Fool's Day is, the long range American model has been hinting at a major storm in this timeframe for multiple forecasts. The timing of this storm and placement has not been precise in each forecast, but the gist that a storm may be present in the few days surrounding April Fool's Day is present. Above, we have the American model's 12 hour precipitation forecast with mean sea level pressure and 1000-500mb thickness in the dashed colored lines. We see a large swath of heavy precipitation on the Gulf Coast aligned in a slanted formation, and this could indicate a linear thunderstorm formation of sorts, possibly a squall line. However, the possibility of if this storm could even happen remains to be determined. As for the snowy side, we see some blues and oranges just north of the southernmost dashed blue line, and it is this line that is the rain/snow line. If this forecast were to verify, we could see as much as 10 inches of snow in northern Missouri. However, as great as some may see that forecast as, the potential in my eyes is too low for this exact forecast to verify. We will need many more days of model watching to see if any other forecasting systems catch on, or if the storm potential dies out completely (you might think that the premise is obnoxious, but it happens dozens of times per year).


Friday, March 22, 2013

Palm Sunday 2013 Significant Winter Storm -- First Call

First accumulation map rides on most recent model trends and accounts for model majority. Current thinking is a major snowstorm will erupt from the Rockies and produce major accumulating snow across much of the Plains, Midwest and Ohio Valley. Latest model trends support amounts over one foot in some isolated areas, and it is these areas that are in the lowest confidence zones.

For my first forecast, I am predicting a light accumulation zone of 1-3 inches in the Lower Great Lakes and far northern Central Plains states like northern Nebraska and northern Iowa. Recent model trends have been showing these amounts, and in accordance with what seems to be the final track, I agree with model guidance on those amounts. General 4-8 inches is predicted from the Front Range in Colorado across the midsection of the Plains, through the southern Midwest and into the Ohio Valley. I'm liking the higher end of that scale for portions of central Nebraska, north central Kansas and towards I-80 in Illinois and south of Gary, Indiana. Darker blue depicts 8-12 inch forecasts. I expect these amounts to be most prevalent from northeast CO into border counties of Nebraska and Kansas. Keep in mind that this zone is uncertain, and will likely take another ~12 hours to determine where (and if) that higher accumulation zone sets up. A west to east line continues with the 8-12 inch predictions, cutting through northern Missouri and Central IL/IN into Ohio. Isolated spots in central Illinois, central Indiana and central Ohio could see 12 to 16 inches out of this event, more likely in the lower end of that spectrum.


Thursday, March 21, 2013

Palm Sunday 2013 Significant Winter Storm (Updated 3/21)

Model guidance has come into line with its first consensus for the storm. The model choice is for the storm system to drop well into the Plains before skirting to the east-northeast/northeast up the southern Midwest region and into the Ohio Valley. This track would blanket portions of Illinois, Indiana, Ohio and more Plains states out west with snow that could reach beyond one foot, especially in the Midwest. Shown above are four model guidance members, with the Canadian model in the top left, the American model in the top right, the European model in the bottom left and the United Kingdom's model in the bottom right. Due to timing issues, this is the best depiction I could get of the storm at tis timeframe, which is 96 hours away (4 days away). The colors shown are 500 millibar heights, while the mean sea level pressure values are shown in black contour lines. The Canadian and European models are sticking to a solution that has the storm in the Midwest/Ohio Valley at this timeframe, while the American and United Kingdom models favor the system being offshore by the time Hour 96 rolls around. This shows how there remains considerable uncertainty in the track even though we are only a few days away.

Notes on model guidance... Slight trend north has been observed with most recent forecasting guidance, will have to watch this as models tend to bring the storm to the north after dropping south, like we saw the models do with this storm. Model uncertainty remains too great to pick any particular forecast.

Analysis of multi-model snowfall forecasts above shows a clear consensus on where the heaviest snow should fall. Portions of Illinois, Indiana and Ohio are likely to receive the brunt of this storm system, with accumulating snow continuing out to the Plains and possibly into the Northeast. Short range American NAM model takes the storm's snowfall a bit further to the south than other model guidance, bringing snows just over 1 foot into Ohio and a portion of Indiana. Nebraska and Kansas are also hit hard. American GFS model hits the same areas with heavy snow, but is slightly weaker in Illinois and Indiana. European model blows up the snow in IL/IN/OH, with formidable snows back out to the west. Canadian model is in its own world, I have no desire to take its solution seriously.

NOTE: Nebraska SHOULD be included in this graphic, time constraints would not allow me to go back and put NE in.
Current thoughts are shown above, with a wide stripe of accumulating snow potential from Kansas and Nebraska (even though NE is not marked, it is in the stripe) into the southern Midwest and Ohio Valley, continuing through the Northeast. I am feeling confident of NE/KS/MO getting in on an accumulating snow event, however confidence drops when we reach the Midwest and Ohio Valley. The storm track is not set in stone just yet, and we could very well see a shift further north in the next 24 hours. I did put the Northeast in this graphic in the chance that some snow does hit that area. Again, even though model forecasts aren't too supportive, there is lots of time for change. I will put in amounts when models clear up further, probably in tomorrow afternoon's update.


Wednesday, March 20, 2013

Palm Sunday 2013 Potential Significant Winter Storm

Model guidance remains disorganized as far as where this storm will go. The past 24 hours have seen model guidance stage a southward shift, now bringing the storm through the southern Midwest and into the Ohio Valley. This track would bring the heaviest snow more into the southern Midwest, Plains and portions of the Ohio Valley. Models shown above are the Canadian model (GEM), American model (GFS), European model (ECMWF), and the United Kingdom's model (UKMET). The forecast period is for Hour 96, which is 4 days away from today, and is forecasting 500 millibar heights in colors and pressure values in the black contour lines. Canadian, European and United Kingdom model guidance prefers a southern track, which would take this system through the southern Plains into the far southern Midwest and northern Gulf Coast states, before moving offshore and possibly instigating a disturbance out there, although model guidance is too great to divulge anything further than that for the Northeast. European model has definitely been more consistent than other guidance, with a solid track of having the storm go through the southern route. Other model guidance has been catching on as of late, with all but the American model pulling for a southern track.

Rather than just stare at the models and see what we can get out of them, let's look at the projected atmospheric set-up and see what the atmosphere is most likely to do with this system. This is the forecasted 500 millibar height anomaly from the American ensembles (also supported by at least one other ensemble system), where cold colors indicate low pressure and warm colors depict high pressure. This forecast is valid as the storm is moving towards the Midwest and Ohio Valley. We'll start off with the monumental high pressure system over northern Canada and Greenland. This type of set-up is one that typically allows storms to be suppressed to the south. In that vision, the European model's idea of the storm taking the southern route is not that far-fetched. However, there is an obstacle that must be overcome for this storm to be pushed far enough south to validate the European model's idea.

When the storm falls down into the Plains to begin its trek either east or northeast, it will naturally provoke high pressure in the Eastern Seaboard. This can be anticipated by the general idea that the low pressure system pushing down will force high pressure to form and push up to equal out the stress inflicted on the atmosphere. Because of this high pressure in the Eastern Seaboard, the storm could very well want to take the northern route and bring heavy snow to the Lower Great Lakes and northern regions of the Midwest, like I showed yesterday. Previous model forecasts enticed the idea of that ridge acting on the storm system and sending it north, but more recent guidance has the ridge being overwhelmed by the low pressure system, which is also very possible.

Here is my top analog for the upcoming Palm Sunday 2013 winter storm. I analyzed multiple analogs from the St. Louis University website, and chose the one with the highest correlation with the latest GFS forecast at the 300 millibar level and 500 millibar levels. These two levels are the most crucial in analog forecasting, as they project the jet stream pattern and high/low pressure alignment, both of which are key in this storm system in particular.

Considering how model guidance has tended to bring storms to the north just a day or two before the event happens, I'm not willing to discount either solution right now. I think both the northern solution and southern solution have valid reasoning and solid evidence as to why each could happen. The next 48 hours will be crucial to see incoming model forecasts as the storm edges closer to shore.


Tuesday, March 19, 2013

Palm Sunday 2013 Potential Winter Storm

There is indeed potential for a winter storm from March 23rd to March 25th.

We will do a model overview today. All models are forecasting Hour 144 (6 days away), and are showing 500 millibar heights in colors with sea level pressure in contour lines. To start, we will analyze the American GFS model. This model takes the storm into the southern tip of Lake Michigan at a minimum pressure of 992 millibars, considered pretty strong for an onshore storm system. Typically, storms will easily exceed that strength offshore in the Pacific or Atlantic, but close to 990 millibars onshore, while not infrequent, is relatively uncommon. Regardless, the storm system is taken through the Great Lakes, allowing significant snow to bury the Midwest and Great Lakes, upwards of one foot in many states west of Lake Michigan and into the Plains.

The general synopsis that is probable to happen is a storm system dropping from the northwest into the Plains, and then moving either east or northeast to bring winter weather to people in the north and severe weather to people in the south. The models are having trouble with grasping how far south the storm will end up dropping into the Plains and what direction the storm will head after encountering the high pressure in the Southeast and East US when the system is in the Plains.

We're going to move onto the foreign models now, and we start that part of this post with the Canadian model. Before I get into this model, know that it is notorious for being unreliable with storms and should not be trusted easily, no matter how amazing the solution is. The Canadian model has this storm system moving through south-central Illinois, dropping over half a foot in cities like Chicago, Gary, maybe even into Iowa (I haven't had an opportunity to see precipitation charts, just a few meteograms). The Canadian model drops this storm to 998 millibars, suprisingly weaker than the American model. The reason it is so surprising is because its usually the Canadian model over-exaggerating a storm's strength and not the other way around. Something to watch for the future? You bet.

We now go onto the United Kingdom's model. Because the phrase United Kingdom is too long to type every time I mention the model, I will refer to this forecasting system as the UKMET, its official model name. The UKMET sees this system weakly progressing in a track from Alabama to Ohio that would bring severe weather to the Southeast and snow to the southern Midwest. This is the weakest model yet of the three we have seen thus far, and its track is the third option of the three models. As you can already tell, the chances of figuring out a track for this system today are quite low.

The last of our foreign models is the European model. While it is typically regarded as the top forecasting model in the world as far as accuracy goes, I have been seeing a recent drop-off in its accuracy, and you may want to note that when taking this forecast into account. The European model doesn't show the system anywhere near the Midwest. If you look closely, you will see it off the coast of the Mid-Atlantic. It has cut across the South and prohibited any major snow event from occurring in the Midwest or Ohio Valley. While it is the fourth different solution from the four models we have seen, the European has been rather consistent with its idea of a storm system offshore the Carolinas for at least two runs. In the other models defense, the American GFS' idea of a major snow event in the Midwest, Great Lakes and Plains has been trending as well. Looks like the traditional American vs European model battle is setting up here, with the other foreign models just doing their own thing.

I did take a look at a few ensemble sets. Two ensemble sets, the American ensembles and another set called the North American Ensemble Forecasting System (NAEFS) are showing solutions that are very nearly identical. Because the NAEFS does not provide precipitation graphics on the website I used to evaluate these ensembles, I looked at the American ensembles for precipitation. The American ensembles predict a major snowstorm from the east central Plains into the Midwest and Great Lakes. Cities like St. Louis, Chicago, Milwaukee, Detroit and Gary would all be affected, many of them by pure snow. It is also worth noting that the Canadian ensembles and European ensembles keep the storm system further to the south. While the European ensembles cancel out a Midwest snowstorm altogether, the Canadian ensembles still throw a swath of accumulating snow at all of the aforementioned cities. Precipitation charts are not available on the European ensembles.

My current thoughts on this system are solid enough for me to show a swath of significant snow potential and a swath of severe weather potential. I am leaning towards the very weak model consensus that there will be the aforementioned types of weather in their respective regions. The red L's show where current model forecasts have this system, and as you can see, the consensus is loose at best.

Stay tuned to The Weather Centre for daily updates on this potential winter storm.