Saturday, November 30, 2013

December 5-7 Potential Winter Storm

There is an increasing potential for a winter storm in the Midwest, Plains and Great Lakes over the December 5-7 period.

A look at geopotential height anomalies over the middle of the atmosphere from November 28th into the 29th suggest that stormy weather was over East Asia, as evidenced by deep blue negative height anomalies. Using the correlation that indicates weather over East Asia is reciprocated throughout the United States just 6-10 days later, it is expected that stormy weather will be brought upon the US between the December 5-9 period. Model guidance suggests that this potential storm will occur between the December 5-7 period.

Model guidance systems from the GFS (shown above) to the Canadian GEM to the European ECMWF agree that this will not be a huge snowstorm for those that get snow. There is general agreement that a region from Missouri and Kansas to Michigan will get in on some snow for this storm system, with the states of Iowa, Illinois and Wisconsin also getting in on the action.

The GFS model's snowfall forecast for this system (shown above) is actually a bit south of other forecasts from the GEM and ECMWF, as shown below:

GEM Model total snowfall forecast (storm system's snowfall seen over MO/IL/IN/MI)

The European model is obviously much more aggressive with this storm system, and I don't blame it. It will take a little while longer for models to nail down exactly how much precipitation will be in the below freezing air mass, and how much will be in the above freezing air mass. The European solution keeps more precipitation below freezing, while the GFS/GEM agree on more liquid precipitation rather than snow. Regardless of how much precipitation actually ends up in the above and below freezing air masses, it is apparent that someone in the MO/IL/MI region will end up with some accumulating snowfall. I'll stick with the GEM/GFS for now out of caution and a wish to refrain from going all-in on the highest snowfall forecast, but depending on the consistency of each model in the future, my preference may change.

ICYMI: December 2-4 Potential Blizzard

Andrew

December 2-4 Potential Blizzard

There is growing potential for a substantial winter storm to fall upon the Northern Plains and upper Midwest, possibly to blizzard proportions. 

Reanalysis of the weather around East Asia reveals a storm system passed over the region on November 26th, resulting in the apprehension for the chance of a storm system for the nation between December 2nd and December 6th. This storm would appear to be related to that East Asian connection, where weather anomalies in East Asia can be reciprocated in the United States approximately 6-10 days later. Model guidance is now catching on to what may be a blizzard in the December 2-4 timeframe.


Precipitation type and MSLP projections for December 3rd, when this storm is at its peak, show very heavy snow impacting the Northern Plains, including the Dakotas and Minnesota, as well as the Upper Midwest (with Wisconsin and the Michigan peninsula included). The storm's minimum pressure looks to be in the 980 millibar range, which classifies this as a very strong storm system. This is confirmed by the tight pressure contour arrangement around the storm system. With the tightening of those pressure contours comes increased winds, and this is why my concern is shifting towards a blizzard threat. It remains to be seen if the criteria for a blizzard will be met, but based on current model projections, I wouldn't take that idea off the table.

Snowfall amounts from this storm range from half a foot in far North Dakota to over a foot in southeast ND and a portion of South Dakota. Totals above the 12 inch mark are widely projected across Minnesota, extending into Wisconsin before a drop-off to the 6-12 inch range is seen across the Badger State. I'm generally anticipating amounts close to this forecast, as a system as strong as this one will be capable of producing some rather large snows.

Andrew

Friday, November 29, 2013

December 4-8 Major Winter Storm

It is looking increasingly likely that a winter storm will affect the Plains over the December 4-8 timeframe.

Height anomalies over East Asia in the last several hours suggest the passage of a bout of stormy weather, centered over Japan. This is signified by the deep blues and indicate the presence of such stormy weather. There is a known correlation that indicates storm systems or ridges of high pressure over East Asia can be reciprocated in the United States 6-10 days after the event's occurrence in East Asia. As we see a stormy period begin in East Asia over November 28th, I would expect December 4-8 to be the timeframe for a winter storm in the US as a result of this East Asian correlation. Now that we have been tracking the models for the past several days, and have taken the Lezak Recurring Cycle into account, we are getting some returns on possible tracks for this storm system.

The Lezak Recurring Cycle would indicate that the storm system that passed through the Plains on October 11th should come back to haunt the region, roughly around the December 7th timeframe. As the mid-level chart from October 11th shows above, the system brought its strongest impacts to the Dakotas and Northern Plains, though I suspect that won't be completely the case this time around. For those unfamiliar with the concept, the Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a 40-60 day interval for the next ~10 months before it dissipates over the following summer. This season's cycle is roughly 57 days, which is why we have highlighted December 7th as the connection date for this October 11 system.

The GFS model has this storm system actually becoming two storm systems, though it is the northern-most one that drops snow across the Plains. This model puts down snow from Montana to Wisconsin, also allotting some snow to the Dakotas, Minnesota and Canada. With the presence of an Arctic front pushing south, I support this idea of the system taking a more zonal approach to its track when compared to the October 11th track. While model forecasts will continue to change until this storm system, I do think that more of the upper Plains and upper Midwest will experience the wintry side of this storm when compared to the portion of those affected in early/mid October.

The GFS model puts down totals in excess of one foot across North Dakota, much of Minnesota and a slight portion of Wisconsin. Lower amounts greet the other half of the Dakotas, the rest of Minnesota and the upper half of Wisconsin. This does look to be a rather substantial event, should current forecasts verify, with plowable snow extending across a wide majority of the far northern states.

Andrew

Tuesday, November 26, 2013

December 7-11 Potential Winter Storm

The potential is on the rise for a winter storm between the December 7 and 11 timeframe.


Ensemble forecasts place some stormy weather around Japan in time for the first day of December, as a major pattern shift in the Pacific gets underway.There is a known correlation that indicates storm systems or ridges of high pressure over East Asia can be reciprocated in the United States 6-10 days after the event's occurrence in East Asia. Thus, seeing the potential for a storm system in Japan on December 1st, it would be assumed that December 7th to the 11th is the timeframe for a potential winter storm in the United States.


Adding to this potential winter storm system's credibility is the Lezak Recurring Cycle. The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a 40-60 day interval for the next ~10 months before it dissipates over the following summer. Now that we are in late November, we have already begun to enter the next cycle of the LRC. There was a storm system that moved through the Plains and Midwest from October 14th-15th, which brought precipitation to those regions. Now, roughly 57 days later (the approximate length of the LRC cycle this season), we are looking for this storm to come back around December 10-12. This places it just outside of the timeframe set forth by the East Asian correlation, but I have a feeling that the two ought to combine in this case to produce the winter storm chance.

Going strictly by the LRC, one would expect the Plains and Midwest to get this storm system again. But, if teleconnection forecasts verify at their current projections, it's possible the system goes further north than it did in mid-October, or gets caught in the subtropical jet stream and stays to the south. I personally prefer the upper Plains-upper Midwest track, but in this case, time will tell.

Andrew

December 4-8 Potential Significant Winter Storm


As the image above shows, there will be a rather deep area of negative height anomalies over East Asia for November 28th, as exhibited by the dark blues in the top left of the left-hand panel. There is a knwon correlation that indicates storm systems or ridges of high pressure over East Asia can be reciprocated in the United States 6-10 days after the event's occurrence in East Asia. As we see a stormy period begin in East Asia over November 28th, I would expect December 4-8 to be the timeframe for a winter storm in the US as a result of this East Asian correlation. There are already a couple of guesses put out by the ECMWF control run. The most recent forecast has an absolutely colossal trough emerging over the Plains, possibly of historical proportions:



This geopotential height anomaly forecast from the ECMWF ensemble control run has this massive trough really ramping up between December 4-5, before getting to its peak on the evening of December 5th. The sea level pressure forecast for this storm would put it below 980 millibars, meaning this potential storm system would have a MSLP value in the 970mb range. That is the equivalent of a Category 2 hurricane, judging solely by MSLP values.

Please bear in mind that such a solution has a very slim chance of working out as it is shown. The reason is because it is still quite a ways away, but the East Asian correlation means that a storm system somewhere in the Plains (or East US, for that matter) is possible. To this magnitude? Probably not. But a storm system somewhere in the US? Very possible.

Just as a little eye candy, here's the snowfall forecast from that mega-storm forecast. USE WITH CAUTION!!



Andrew

Long Range Lookout: Early-Mid December Looking Very Cold, Snowy

It's looking like early to mid December will be very cold, and quite possibly snowy across much of the nation.

Relative atmospheric angular momentum values for the last couple of months tell the story, as we have seen an emergence of positive AAM anomalies above the 60N latitude mark, as shown by the yellow blob near the top right part of the image. Without going into the technical aspect of the AAM, it is known that positive AAM anomalies above the 60N latitude line, with -AAM anomalies below that parallel can lead to favorable winter weather conditions across the country. In this case, a recent spike in AAM anomalies across the upper latitudes is now leading to the emergence of ridging near the Arctic, as I will show later on in this post. The -AAM anomalies persist across the mid-latitudes, confirming the suspicion that wintry weather will be here to stay for a little while.

Image created by Nicholas Schiraldi
The GFS Ensemble forecast for the AAM over the next couple of weeks reiterates the trend we have been seeing, with negative angular momentum anomalies keeping a tight grasp on the mid-latitudes in the days ahead. Positive AAM anomalies are projected to dissipate, but the aforementioned -AAM persistence in the mid-latitudes should keep at least a slightly wintry gun aimed at North America.

East Asia is projected to be rather stormy over the next handful of days into the latter part of early December. As I've mentioned on this blog, weather anomalies over East Asia have been found to affect weather in the United States 6 to 10 days after the occurrence in E. Asia. This means that when stormy weather hits Japan, it can be expected that stormy times will greet the US just 6-10 days later. The ECMWF ensemble system has been predicting that Japan will encounter some rough weather in the next couple of weeks and slightly beyond. This includes the passage of potentially several storm systems. If correct, this would greatly raise the possibility of snowy weather turning up in the United States just a few days later. It's a little too early to eye particular dates for this East Asian / US winter storm correlation, and it may be a little while before this stormy East Asian projection still holds value on the ensemble forecasts in a few days.

Now, this projected East Asian storminess will come as a massive shift in the Pacific gets underway. It is predicted that a huge ridge of high pressure will take up residence in Alaska and the Gulf of Alaska in the opening week of December. This ridge will then transition to an Omega Block pattern, which forms an atmospheric pattern not unlike that of the Greek letter Omega, as the illustration below shows.

The Weather Prediction
This Omega Block in the Gulf of Alaska will really dominate the northern Pacific during its tenure in those waters. The ridge is expected to develop gradually until it finally bursts north and actually penetrates into the upper latitudes. With the presence of such a strong ridge, deep negative mid-level geopotential anomalies will develop in the Western US. This means that cold weather will be a prevailing feature for the West US into the Plains, as well as the Midwest, Great Lakes, Central and Southern Plains regions in conjunction with the teleconnection pattern, which we will discuss later.

Nearly a week after the ridge takes up residence in the Gulf of Alaska, the ECMWF ensemble prediction system (EPS) indicates the ridge will retrograde west and into the Bering Sea, still remaining in an Omega Block formation. This Bering Sea ridge may actually try to work out a Rex Block pattern with East Asia, where ridging in the Bering Sea may slide west further and provoke negative geopotential height anomalies across East Asia in typical Rex Block fashion. If that were to play out, East Asia would get pretty stormy, and as we discussed above, this would have stormy implications for the United States. However, because this is all long range in nature, I won't speculate too much on that potential. The ensemble set predicts that troughing will persist in the West US, and that would be a byproduct of another ridge popping up in the eastern Gulf of Alaska. This feature will determine if the Bering Sea ridge will transition to a Rex Block or remain an Omega Block. If it does go into a Rex Block, the ridge will slide westward, and the Gulf of Alaska ridge, should it be a separate entity, would allow troughing in the West US to continue- a bad sign for US winter weather folk. However, if it keeps its initial Omega Block form, ridging in the Gulf of Alaska should dissipate and instead be replaced by negative geopotential height anomalies. This would produce a favorable winter weather pattern for the US. This is all to be determined, and I'm not willing to go beyond analyzing the possibilities for diagnosing this particular situation.

Coming out of this massive ridging in the Pacific will be a very negative West Pacific Oscillation and East Pacific Oscillation, nicknamed the WPO and EPO respectfully. The two indices are very closely related, and they should react very similar when this Omega Block ridge begins to spread its influence across the Pacific. When that ridge forms, the WPO and EPO are likely to maintain their negative phase, as the negative phase of each index calls for ridging across the Pacific. The -WPO and -EPO also call for cold air to hit the West US, and then bleed east into the Plains and Midwest, before finally reaching the Mid-Atlantic/Northeast and Southeast. With the massive ridge in the Pacific producing the troughing in the west, it all looks primed for a textbook -WPO/-EPO response, with dramatic cold weather anomalies in the Plains that modify and push east with time. To summarize, this late November cold weather is only a sliver of what's to come.

Long range analogs created by the Climate Prediction Center and the GFS ensemble system confirm the idea that this Pacific ridge will create some very cold weather in the West US and the Plains, but also hint that it could set up some cross-polar flow for North America. What is cross-polar flow? When a ridge like the one we are discussing now sets up in the Pacific, it can shoot north and push the jet stream way north, even into the Arctic Circle. The jet stream carries cold Siberian air eastward as usual, but rather than send it towards the Bering Sea, the ridge in the northern Pacific bumps the jet stream north and then south, into North America. In a nutshell, a cross-polar flow event is the motherlode of cold weather, so to speak. If the analogs are true and the Pacific ridge can sustain itself at such a magnitude, then this cross-polar flow idea is a valid one in the long range.

Early and mid December is the prime target for some brutally cold weather, along with a side of snow potential. Just how cold and snowy it will get remains to be seen, but it's true: the potential is there.

Andrew

Monday, November 25, 2013

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

Sunday, November 24, 2013

December 4-8 Potential Winter Storm

It looks rather possible that the US will experience a winter storm around the December 4-8 time period.

As the image above shows, there will be a rather deep area of negative height anomalies over East Asia for November 28th, as exhibited by the dark blues in the top left of the left-hand panel. There is a knwon correlation that indicates storm systems or ridges of high pressure over East Asia can be reciprocated in the United States 6-10 days after the event's occurrence in East Asia. As we see a stormy period begin in East Asia over November 28th, I would expect December 4-8 to be the timeframe for a winter storm in the US as a result of this East Asian correlation. There are already a couple of guesses put out by the ECMWF control run. The most recent forecast has a storm system targeting the Midwest and Great Lakes for snow, as shown below (note the yellow arrow denoting the storm track)...

ECMWF Ensemble Control MSLP anomaly projection for December 5th
The second-newest ECMWF control run actually develops a stronger storm towards the end of this December 4-8 timeframe, unlike the December 5th projection from the ECMWF control...

ECMWF Ensemble Control MSLP anomaly projection for December 8th
As you can see, there is still a lot of time for this to be figured out, and the level of uncertainty is very high as far as who may be affected. What I am decently certain of, though, is that there is a chance for a winter storm in this timeframe.

Andrew

Arctic Outbreaks Herald Start of December


A very cold pattern will herald the start of December, and unofficially the start of winter 2013-2014.

The ECMWF ensemble system and GFS ensemble system forecasts agree that we will see a pattern develop in the next 10+ days which will include two substantial bodies of high pressure in the northern Atlantic and Pacific. The Bering Sea will possess one half of the ridging system, while Greenland attempts to reel in the second component. These two ridges are then projected to split the polar vortex into two pieces, one of which will slide down into Europe, while the other pushes down into North America. 

It is expected that there will be a prolonged period of lower pressures across North America in the first couple of weeks of December, and this will lead to below normal temperatures for much of the nation. It is anticipated that this cold air will originate from Canada and will be transported from the Northern Plains into the Central Plains on east. Temperature anomalies from both ensemble systems have deep below normal anomalies stretched out across nearly all of the country. The likelihood of this prolonged cold weather is rather high, as the stratosphere will also be undergoing a Wave-2 response to two high pressure systems applying pressure in just about the same areas as the ensemble projection above shows.




Now, there are two main types of stratospheric events that disturb or split the polar vortex. There is a Wave-1 response, which involves the polar vortex becoming elongated and/or weakened, however a split does not occur. This can result in displacement of the vortex out of the Arctic, but that prospect is not as likely as it is in a Wave-2 scenario. A Wave-2 stratospheric response involves the polar vortex being split into two main vortices, as the image from NASA shows above. While the temperature images show the Wave-1 and Wave-2 (top and bottom rows, respectfully) responses occur over Greenland and Eurasia, especially with the two split vortices where one vortex goes over Greenland and one goes into Eurasia, the split can lead the vortices into any land mass, not just those two regions.


The ECMWF Ensemble set confirms the idea of a particularly harsh outbreak of cold weather to kick off December just over a week in...




Andrew

Saturday, November 23, 2013

December 2013 Weekly & Monthly Forecast

This forecast will give depictions of the conditions for each week in December by text, and then graphics for the monthly averages.

Weekly Forecasts

December 1-7: It appears possible that there will be another outbreak of Arctic air from Canada into the United States. Both American and European ensemble guidance systems confirm this idea, thus it is anticipated that this timeframe will be quite cold. It appears that the precipitation anomalies would be most enhanced over the Plains, Midwest and Ohio Valley with a favorable Pacific pattern, though the East Coast will also need to monitor this timeframe as ridging pops up near Greenland to provide a base for a possible negative North Atlantic Oscillation.

Plains: Very Cold, Possible Above Average Precipitation.
Midwest: Very Cold, Possible Above Average Precipitation.
Ohio Valley: Cold, Possible Above Average Precipitation.
Northeast: Very Cold, Average Precipitation.
Mid-Atlantic: Cold, Average Precipitation.
Southeast: Cool, Average Precipitation.
South Plains: Cool, Possible Below Average Precipitation.
Southwest: Warm, Possible Below Average Precipitation.
Northwest: Average Temperatures, Possible Above Average Precipitation.

December 7-14: The cold pattern should continue, but slowly wind down towards the end of this week. Watch out for a winter storm during this timeframe, which may affect the Midwest or East Coast based on the early week teleconnection patterns. Expect warm weather in the West to continue, but possibly edge eastward as the colder weather does begin that winding down trend.

Plains: Cold, Possible Above Average Precipitation.
Midwest: Cold, Possible Above Average Precipitation.
Ohio Valley: Cold, Possible Above Average Precipitation.
Northeast: Cool, Average Precipitation.
Mid-Atlantic: Cool, Average Precipitation.
Southeast: Average Temperatures, Average Precipitation.
South Plains: Average Temperatures, Possible Below Average Precipitation.
Southwest: Warm, Possible Below Average Precipitation.
Northwest: Average Temperatures, Possible Above Average Precipitation.

December 14-21: The cold pattern that kicked off December should have receded by now, and may very well give way to a warmer than normal pattern. If not warm weather, expect an altered precipitation anomaly pattern, which may shift away from the Midwest and Ohio Valley to the Plains once again.

Plains: Warm, Possible Above Average Precipitation.
Midwest: Warm, Possible Below Average Precipitation.
Ohio Valley: Average Temperatures, Average Precipitation.
Northeast: Average Temperatures Average Precipitation.
Mid-Atlantic: Average Temperatures, Possible Below Average Precipitation.
Southeast: Average Temperatures, Possible Below Average Precipitation.
South Plains: Warm, Possible Below Average Precipitation.
Southwest: Cool, Average Precipitation.
Northwest: Average Temperatures, Average Precipitation.

December 21-31: The remaining week and 3 days of December are rather murky, as it is not known just how long this potential warm pattern will last. Depending on upcoming stratospheric developments, this timeframe may or may not see an active weather pattern. There are no significant signals of either active or non-active weather for this period, so the forecast for this timeframe will follow that of the previous week, but is highly uncertain.

Plains: Warm, Possible Above Average Precipitation.
Midwest: Warm, Possible Below Average Precipitation.
Ohio Valley: Average Temperatures, Average Precipitation.
Northeast: Average Temperatures Average Precipitation.
Mid-Atlantic: Average Temperatures, Possible Below Average Precipitation.
Southeast: Average Temperatures, Possible Below Average Precipitation.
South Plains: Warm, Possible Below Average Precipitation.
Southwest: Cool, Average Precipitation.
Northwest: Average Temperatures, Average Precipitation.

Monthly Averages

Temperatures for the month of December will most likely be determined by the first week or two of the month, with significant cold weather anomalies across much of the nation. Temperatures ought to vary from frigid conditions in the Plains, where the Arctic air will originate from, to cold weather in the Midwest and cool conditions in the Northeast. Average conditions may prevail over the Southwest before slightly above average temperatures show themselves along the West Coast.

Precipitation anomalies are set up in accordance with the first few weeks of the month, with a wide, rather uncertain swath of above normal precipitation stationed over the Plains, Midwest and Great Lakes. The Great Lakes will be inundated with lake effect snows as a result of the cold outbreak at the beginning of the month, with another one possibly following close behind. Other areas of the nation are too uncertain to delineate, but we will most likely see precipitation anomalies outlined in the first days of the month.

Andrew

Friday, November 22, 2013

Thanksgiving Potentially Significant Nor'easter

I believe that the probability of a Nor'easter around the timeframe of Thanksgiving is now high enough to be labeled as potentially significant.


Model guidance has been somewhat consistent on the development of a coastal storm system out of two pieces of energy, one from the Gulf Coast and one from Canada. The prognosis right now is that the piece of energy along the Gulf Coast will push east along the coast before the Canadian energy drops down far south enough to pick up the coastal energy. When the two pieces of energy begin to interact, it is expected that the Canadian energy will pick up the Gulf Coast system, the two will shift northeast and form one coastal storm system that will then become a full-blown Nor'easter. Now, model guidance is not completely on board with this system. The European ECMWF model has been in favor of a Nor'easter for a while, but the GFS model has been flipping back and forth between a storm or no storm. For reasons of consistency with the ECMWF, and agreement among the prestigious ECMWF ensemble prediction system (EPS), we will go with that model system.



Precipitation projections are tricky right now, as model guidance is still not 100% sold on the Nor'easter even occurring. However, if it is to occur, it is anticipated that coastal regions will receive rain while inland areas get potentially significant amounts of snow. This is due to a variety of factors, including the proximity of the storm to land, the anomalously warm water temperatures along the coast, and the fact that it's only November, and therefore there will still be warm temperatures to interfere with snow prospects for some areas.



This ECMWF image gives you an idea of what kind of snowfall could be seen with this storm system if it occurs as is shown right now by the model system. It is still subject to potentially drastic change, so this is just shown to give you an idea of possible snowfall amounts with this storm.

So, what do we have to go on that supports this potential likely winter storm? We'll start with data I discussed on Wednesday's post.

As I've told on this blog, there has been a storm forecast to hit East Asia just two days ago. It ended up verifying, and the text from a post on that discussion a handful of days ago is below.


This is a forecast from the GFS Ensembles out to the Hour 60 timeframe. While all of the colors and lines may seem a little overwhelming, we're only going to focus our attention on East Asia, which is under the deep blue swath in the top left part of the left panel. Another correlation that has been proved effective is how weather in East Asia can be reciprocated in North America 6-10 days after the weather anomaly in East Asia. This includes the presence of storm systems or high pressure in East Asia. The November 18 forecast from both the GFS Ensembles and ECMWF model indicates that a deep negative height anomaly swath will slide down over Japan. If we extrapolate November 18th six to ten days out, we come up with a potential cold weather and storm system time frame of November 24 to 28. This narrows down the timeframe previously set out by the Bering Sea correlation, and if we match up the two timeframes (November 24-28 for the East Asian connection and November 25-29 for the Bering Sea connection), we come up with a November 24-29 potential timeframe for a storm, which can be isolated into the November 25-28 period, which is shown by both connections. Based on these two connections coming up with a common timeframe for a potential US storm system, confidence is quickly rising that this event will happen. 

The evidence doesn't stop there- here's text from a post on this storm potential I made back on November 13:


Take a look at the Bering sea in this two-panel reanalysis of the weather on November 8th. If you look closely, you can see that the Bering Sea was in the midst of a decent storm system on this date, just three days ago from today. This storm system passed along those waters in the midst of a mammoth ridge of high pressure just to the south. The 500mb height anomaly chart on the left best reflects this storm system, but its presence is confirmed on the right panel, which displays mean sea level pressure contour lines and denotations, as well as cloud cover. This Bering Sea storm has a connection to this potential Thanksgiving winter storm. Based on research done by Joe Renken, weather in the Bering Sea correlates to weather here in the US approximately 2.5 to 3 weeks after the Bering Sea weather anomaly occurs. This storm system in the Bering Sea happened on November 8th, and extrapolating that out 2.5 to 3 weeks ( 17-21 days) leads us to a potential storm system impacting the US around November 25 to 29. Considering November 28th is Thanksgiving, there does appear to be at least decent potential for a winter storm around the Turkey Day timeframe. (End post)

The East Asian and Bering Sea correlations alone are enough for me to be decently confident in this event occurring, but there are other items that further enhance the probability of a winter storm along the East Coast.


This is the North Atlantic Oscillation forecast from the ECMWF for the next 10 days. The North Atlantic Oscillation, or NAO, involves pressure anomalies over Greenland that influences synoptic weather over North America, and around the world. The positive phase of the NAO involves stormy weather around Greenland, and this translates to warmer weather across the US, as well as a zonal flow across the nation. The negative NAO comes about from high pressure stationed over Greenland, and this permits cold weather to enter the East US, and enhances the chances of a coastal storm. The area where this storm may occur is circled in red, and as you can see, the model projects the NAO to be switching phases during this timeframe. It has been demonstrated that when the NAO is switching phases, coastal storms become more likely. Thus, it isn't such a far-fetched idea that a Nor'easter could occur in the day or two prior to Thanksgiving, possibly into Thanksgiving itself.

(Image removed for security purposes)

Now, I've discussed how the GFS and ECMWF are at odds with each other over this storm, but there is one atmospheric feature that they do agree on with this storm system. Both model guidance systems indicate that there will be a rather strong storm system around the far eastern portion of Canada. This is called a "50/50 Low", and is called such because of the presence of a low pressure system around 50 North and 50 West on the latitude and longitude scales, respectively. When a 50/50 Low forms, it is not uncommon to see a coastal storm to occur in the 2-3 days after the phenomenon. That said, I believe the ECMWF when it comes to the projection for this Nor'easter, in addition to the Bering Sea and East Asian correspondents.

I would make an outlook map, but I'd like to wait a bit longer before I do so, mainly because I would like to see the GFS come on board, and I want to see where that snow-rain line places itself, as that will make a big difference in my forecast. But right now, I'm feeling pretty good about a potentially significant coastal storm in a day or two before Thanksgiving, maybe into the actual day of Turkey Day.

Andrew

Wednesday, November 20, 2013

Thanksgiving Potential Arctic Outbreak

It is looking increasingly likely that Thanksgiving will contain a significant cold weather outbreak for much of the nation.

850mb temperature anomalies for the evening of November 27
The ECMWF ensembles and GFS ensembles have been telling of the entrance of a very cold air mass into the US, to the tune of nearly 20 degrees below normal, in Celsius (that's 36 degrees below normal in Fahrenheit). This would most likely bring about the coldest air seen in many parts of the nation thus far, with many in the Plains, Midwest, Great Lakes and Ohio Valley in line for temperatures that may flirt with single digits, like Chicago, or smash right through the single digit mark, like many areas closer to the border with Canada.

ECMWF temperature forecast for the morning of November 27
It remains to be seen if the models are correct in their estimation of a brutally cold Thanksgiving, but right now, it looks like such an outcome is within the realm of possibility.

There is also the potential for a Nor'easter in the day or two before Thanksgiving...

Andrew

Thanksgiving Potential Major Nor'easter

There is potential (keyword here is potential) for a Nor'easter to form along the East Coast in time for Thanksgiving, and if true, may drop copious amounts of snow on the inland Northeast.



The overnight 0z ECMWF model projects a rather strong piece of energy to slide along the Gulf Coast in the few days leading up to Thanksgiving, drifting almost due east as the jet stream allocates the energy in that direction. At the same time, another piece of energy will be dropping south and east from Canada, and if you know what phasing is, you know what happens next. The model then has the Canadian and Gulf Coast energies combine into a single system that forms just off the East Coast to form a strong coastal storm, as the forecast below (valid November 27) shows.



The ECMWF model has this Nor'easter bring massive amounts of snow and liquid precipitation to the Northeast, and spreads the wealth north and east to cover most of the interior Northeast. The minimum pressure is projected to be at 991 millibars, which pretty much qualifies the statement that this would be a substantial coastal storm. 

Now, the new runs of the ECMWF and GFS do not show this happening. The ECMWF takes the southern energy and pushes it out to sea as the two pieces of energy do not merge in time to form this possible Nor'easter. So why bring it up? Well, there is most likely going to be a storm system somewhere in the US in the days just before Thanksgiving. As I've told on this blog, there has been a storm forecast to hit East Asia just two days ago. It ended up verifying, and the text from a post on that discussion a handful of days ago is below.


This is a forecast from the GFS Ensembles out to the Hour 60 timeframe. While all of the colors and lines may seem a little overwhelming, we're only going to focus our attention on East Asia, which is under the deep blue swath in the top left part of the left panel. Another correlation that has been proved effective is how weather in East Asia can be reciprocated in North America 6-10 days after the weather anomaly in East Asia. This includes the presence of storm systems or high pressure in East Asia. The November 18 forecast from both the GFS Ensembles and ECMWF model indicates that a deep negative height anomaly swath will slide down over Japan. If we extrapolate November 18th six to ten days out, we come up with a potential cold weather and storm system time frame of November 24 to 28. This narrows down the timeframe previously set out by the Bering Sea correlation, and if we match up the two timeframes (November 24-28 for the East Asian connection and November 25-29 for the Bering Sea connection), we come up with a November 24-29 potential timeframe for a storm, which can be isolated into the November 25-28 period, which is shown by both connections. Based on these two connections coming up with a common timeframe for a potential US storm system, confidence is quickly rising that this event will happen. 

The evidence doesn't stop there- here's text from a post on this storm potential I made back on November 13:


Take a look at the Bering sea in this two-panel reanalysis of the weather on November 8th. If you look closely, you can see that the Bering Sea was in the midst of a decent storm system on this date, just three days ago from today. This storm system passed along those waters in the midst of a mammoth ridge of high pressure just to the south. The 500mb height anomaly chart on the left best reflects this storm system, but its presence is confirmed on the right panel, which displays mean sea level pressure contour lines and denotations, as well as cloud cover. This Bering Sea storm has a connection to this potential Thanksgiving winter storm. Based on research done by Joe Renken, weather in the Bering Sea correlates to weather here in the US approximately 2.5 to 3 weeks after the Bering Sea weather anomaly occurs. This storm system in the Bering Sea happened on November 8th, and extrapolating that out 2.5 to 3 weeks ( 17-21 days) leads us to a potential storm system impacting the US around November 25 to 29. Considering November 28th is Thanksgiving, there does appear to be at least decent potential for a winter storm around the Turkey Day timeframe.

There is something else that must be noted with the ECMWF model I discussed at the top of this post. There has been discussion that the model has a bias, in which it holds energy in the Southwest US for longer than it ends up being there. I have a feeling that if this bias ends up working out in this situation, we would see the merge occur in the Northeast, resulting in that coastal storm. That is, if the energy in the South is able to latch on to the Canadian energy- in the most recent ECMWF model run, the southern energy was unable to phase with the Canadian energy until it was too late and the potential coastal storm was already off to the Canadian Maritimes. To give you an idea of what the snow forecast might look like if this Nor'easter occurred, take a look at the overnight ECMWF forecast below (warning, don't take this as a legitimate forecast just yet):




What I'm saying is, there really is potential here that needs to be monitored.

Andrew

Monday, November 18, 2013

Polar Vortex Split May Lead to Cool December

A split in the polar vortex as a result of a changing pattern may lead to a colder than normal December.

A look at the relative atmospheric angular momentum chart gives us a good look at what we will be dealing with in the coming few weeks. While the things that go into this chart are complicated, dissecting it is relatively easy. Basically, in order to see wintry conditions over the US, one would want to see positive AAM anomalies propagating upward past the 60N line, with negative AAM anomalies in pursuit, but only propagating to the area below 60N. In the same sense, -AAM anomalies moving north past the 60N line and +AAM anomalies shifting into the regions below 60N would favor a very anti-winter environment. A glance at the current chart reveals that we see a mass of +AAM anomalies pushing up past the 60N parallel, with -AAM anomalies in hot pursuit below the 60N parallel. This tells me that the atmospheric pattern is due for a change, likely in a favorable direction for winter weather lovers in the US.

The change that is coming appears to be in the stratosphere, and will eventually be reflected on the surface.

The ECMWF model has been forecasting the development of a strong Wave 2 stratospheric event, with the development of a polar vortex-disrupting high pressure system that will aid in the cold weather potential for December. The image above shows the Wave 2 response, with the highest values stretched across the far upper stratosphere to the middle of the stratosphere, with a secondary, minor blip on the radar around the jet stream. As we see the +AAM anomalies propagating to the regions above the 60N parallel, I would dare to theorize that this stratospheric response will be at least partially initiated by the AAM development.  If that is to be true, then this modeled Wave 2 response would become far more likely, as the +AAM anomalies are already happening rather than just being forecasted.



Now, there are two main types of stratospheric events that disturb or split the polar vortex. There is a Wave-1 response, which involves the polar vortex becoming elongated and/or weakened, however a split does not occur. This can result in displacement of the vortex out of the Arctic, but that prospect is not as likely as it is in a Wave-2 scenario. A Wave-2 stratospheric response involves the polar vortex being split into two main vortices, as the image from NASA shows above. While the temperature images show the Wave-1 and Wave-2 (top and bottom rows, respectfully) responses occur over Greenland and Eurasia, especially with the two split vortices where one vortex goes over Greenland and one goes into Eurasia, the split can lead the vortices into any land mass, not just those two regions.

This split is confirmed by the ECMWF potential vorticity forecast by Day 10, with one piece of the vortex going into Canada and the other, larger piece heading into Eurasia. Keep in mind that the polar vortex is one huge storm system that holds the pure Arctic air in its place, so when it splits and heads towards land masses, it's bringing that intense cold air with it. If the model projections verify, those in Canada should prepare for a big cold shock for wherever that polar vortex roams; the same goes for Eurasia.


It now looks like the ridge that interrupts the polar vortex will pop up in the area around Greenland, and this is good news for winter weather folk in the East. With the polar vortex splitting and a piece apparently dropping down into Canada, it only makes sense that a strong ridge will form in Greenland to counteract the deep negative height anomalies of the vortex. Ensembles have started to back off on this negative North Atlantic Oscillation (top), and also the Arctic Oscillation (bottom) in terms of how negative they will get, but I'm pretty sure they will end up more negative than neutral, as the ECMWF ensembles show above.

There are the usual caveats of long range forecasting in play here, along with a few other extra items that have not been mentioned. However, as long as the +AAM anomalies do their thing, and the stratosphere responds as it is expected to, I see a possibility of some cooler weather coming in for December. No word yet on how cold, but with a portion of the polar vortex in Canada just a few hundred miles from the US border, I would expect that colder weather to have an effect on the US as well.

Andrew

Sunday, November 17, 2013

PDS Tornado Watch - Illinois, Wisconsin, Indiana

URGENT - IMMEDIATE BROADCAST REQUESTED
   TORNADO WATCH NUMBER 561
   NWS STORM PREDICTION CENTER NORMAN OK
   840 AM CST SUN NOV 17 2013

   THE NWS STORM PREDICTION CENTER HAS ISSUED A

   * TORNADO WATCH FOR PORTIONS OF
     EASTERN IOWA
     ILLINOIS
     NORTHWEST INDIANA
     NORTHEAST MISSOURI
     SOUTHEAST WISCONSIN
     LAKE MICHIGAN

   * EFFECTIVE THIS SUNDAY MORNING AND AFTERNOON FROM 840 AM UNTIL
     400 PM CST.

   ...THIS IS A PARTICULARLY DANGEROUS SITUATION...

   * PRIMARY THREATS INCLUDE...
     SEVERAL INTENSE TORNADOES LIKELY
     SEVERAL LARGE HAIL EVENTS LIKELY WITH A FEW VERY LARGE HAIL
       EVENTS TO 2 INCHES IN DIAMETER POSSIBLE
     SEVERAL DAMAGING WIND GUSTS WITH A FEW SIGNIFICANT GUSTS TO 80
       MPH POSSIBLE

   THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 100 STATUTE
   MILES EAST AND WEST OF A LINE FROM 25 MILES SOUTH SOUTHEAST OF
   SCOTT AFB ILLINOIS TO 40 MILES NORTHEAST OF MADISON WISCONSIN.
   FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
   OUTLINE UPDATE (WOUS64 KWNS WOU1).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
   TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
   AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
   THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
   AND POSSIBLE WARNINGS.

   &&

   DISCUSSION...ONE OR MORE BROKEN BANDS OF SUPERCELLS ARE EXPECTED TO
   DEVELOP THIS MORNING AND RAPIDLY SPREAD EAST/NORTHEAST ACROSS THE
   WATCH AREA TODAY.  GIVEN THE COMBINATION OF MODERATE INSTABILITY AND
   VERY STRONG VERTICAL SHEAR...CONDITIONS WILL BE FAVORABLE FOR LONG
   TRACKED...SIGNIFICANT TORNADOES.  LARGE HAIL AND CORRIDORS OF WIND
   DAMAGE WILL ALSO BE LIKELY.

   AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
   SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
   WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
   500. MEAN STORM MOTION VECTOR 24050.

High Risk Issued for November 17

The Storm Prediction Center has issued a High Risk outlook for today, as the threat for severe weather has been deemed to be very high.

The High Risk has been issued for eastern Illinois and much of Indiana, likely pointing to the Storm Prediction Center's concern over potentially tornadic cells that may develop as they coagulate with one another to form a powerful squall line. Categorical outlooks issued below tell the story; tornadoes and wind are the top two concerns for today.

Hail Outlook

Tornado Outlook

Damaging Wind Outlook
High resolution models have been continually projecting discrete cells in Illinois developing into an extreme squall line over Indiana and Ohio. The cells that develop in northern and central Illinois will have great potential to be tornadic, especially if they become supercells right off the bat. This environment is very dynamic with a 120kt+ jet stream and 60kt+ lower level winds combining with strong winds from the south to produce incredible shear and a very potent place for thunderstorms.

Initiation of these storms is expected around the noon hour Central Time in Illinois, and further intensification will occur explosively until the 3:00 PM hour, before coagulation occurs and the storms race eastward towards the Ohio Valley at over 50 knots, per recent sounding analysis.

This is a dangerous situation. If you are in the Moderate Risk (red) or High Risk (pink) areas on the top image, you are advised to prepare for potentially extreme weather, which may include tornadoes (some strong), potentially extreme damaging winds, and hail. The scope of this now-likely outbreak is displayed on excerpts of the Storm Prediction Center write-up below.

...TORNADO OUTBREAK WITH MULTIPLE SIGNIFICANT TORNADOES AND
   WIDESPREAD DAMAGING WINDS EXPECTED ACROSS THE OH VALLEY AND SRN
   GREAT LAKES REGION TODAY...
...THE DEVELOPMENT OF A SQUALL-LINE APPEARS LIKELY DURING
   THE LATE AFTERNOON ACROSS THE OH VALLEY WITH THE LINE DEVELOPING SWD
   INTO THE TN VALLEY DURING THE EARLY EVENING.
0-3 KM STORM RELATIVE HELICITIES OF 400 TO 450 M2/S2 WILL BE
   FAVORABLE FOR STRONG TORNADOES WITH SEVERAL LONG-TRACK DAMAGING
   TORNADOES EXPECTED TO OCCUR FROM ERN IL ENEWD ACROSS MUCH OF WRN AND
   CNTRL IND FROM LATE MORNING INTO EARLY AFTERNOON. AS CELL COVERAGE
   INCREASES AHEAD OF THE FAST MOVING FRONT...A SQUALL-LINE SHOULD
   ORGANIZE LATE THIS AFTERNOON. WIDESPREAD WIND DAMAGE WILL BE
   ASSOCIATED WITH THE LINE ALONG WITH TORNADOES WITH ROTATING CELLS
   EMBEDDED IN THE LINE. THE SEVERE THREAT SHOULD RAMP UP SOUTH OF THE
   OH RIVER DURING THE LATE AFTERNOON AS CELLS INITIATE SWD ALONG THE
   FRONT. THE POTENTIAL FOR WIND DAMAGE AND TORNADOES SHOULD DEVELOP AS
   A FAR SOUTH AS THE TN VALLEY DURING THE EVENING AS AN EXTENSIVE LINE
   OF SEVERE STORMS MOVES EWD INTO THE UPPER OH VALLEY AND CNTRL
   APPALACHIAN MTNS.
 SEVERAL FACTORS APPEAR TO BE COMING TOGETHER FOR A TORNADO OUTBREAK
   ACROSS THE OH VALLEY. THE FIRST FACTOR IS THAT THE SYSTEM IS
   NEGATIVELY-TITLED AND VERY WELL-ORGANIZED. THE SECOND IS THAT THE
   LOW AND MID-LEVEL JETS WILL BECOME FAVORABLY COUPLED IN THE OH
   VALLEY TODAY COINCIDING WITH AN OUTBREAK OF STORMS ACROSS THE WARM
   SECTOR. THE THIRD IS THAT SUPERCELLS ARE EXPECTED TO REMAIN DISCRETE
   INTO THE MID-AFTERNOON. THESE FACTORS COMBINED WITH EXTREMELY
   FAVORABLE LOW-LEVEL SHEAR PROFILES JUSTIFIES THE ISSUANCE OF A HIGH
   RISK ACROSS ERN IL...IND AND SW LOWER MI.

Andrew

Saturday, November 16, 2013

November 24-28 Winter Storm

It is likely that there will be a winter storm in the days prior to Thanksgiving.

This is a forecast from the GFS Ensembles out to the Hour 60 timeframe. While all of the colors and lines may seem a little overwhelming, we're only going to focus our attention on East Asia, which is under the deep blue swath in the top left part of the left panel. Another correlation that has been proved effective is how weather in East Asia can be reciprocated in North America 6-10 days after the weather anomaly in East Asia. This includes the presence of storm systems or high pressure in East Asia. The November 18 forecast from both the GFS Ensembles and ECMWF model indicates that a deep negative height anomaly swath will slide down over Japan. If we extrapolate November 18th six to ten days out, we come up with a potential cold weather and storm system time frame of November 24 to 28. This narrows down the timeframe previously set out by the Bering Sea correlation, and if we match up the two timeframes (November 24-28 for the East Asian connection and November 25-29 for the Bering Sea connection), we come up with a November 24-29 potential timeframe for a storm, which can be isolated into the November 25-28 period, which is shown by both connections. Based on these two connections coming up with a common timeframe for a potential US storm system, confidence is quickly rising that this event will happen.

The question now is, where will this storm system go?

European ensemble projections of the North Atlantic Oscillation (top) and the Arctic Oscillation (bottom) are negative for the timeframe of this storm system. This suggests that the storm system should be sucked into the subtropical jet stream, and ought to go along the South US. The Arctic Oscillation going negative for this system's timeframe tells me that the chance of cold air for the North and Northeast US will be on the rise, and this would theoretically aid in the potential for snow in those regions.

The ECMWF projection for the Pacific-North American index has been consistent with the index rising for the timeframe of this storm system. This would allow ridging to form along the West Coast, and help out the chances for this storm system going to the Midwest and Great Lakes. I'm hesitant to believe thoughts that the positive PNA will automatically force this system to head to those regions, as the negative NAO, if it grabs ahold of this system, will wield a good deal of influence on the track, so long as the system does get into the subtropical jet stream. Model solutions have been variable, but here's my early projection for this scenario.

Andrew