2013-2014 Winter Update: Early November, 2013

This update on the 2013-2014 winter will address what has changed and what has not since the Final 2013-2014 Winter Forecast, as well as what the changes say about the upcoming winter.

What Has Changed

Prognosis on the Arctic Oscillation
The Arctic Oscillation is now anticipated to be rather positive this winter, as October SAI data, when accounted for the full 31 days of the month, shows a rather flat change from October 1 to November 1 over the SAI index area. This tells us that the Arctic Oscillation may not be as negative as previously thought. Also hurting the prospects of a negative Arctic Oscillation is the predicted positive AO for much of November. It is shown that the November Arctic Oscillation value can translate on a positive correlation for the following winter 68% of the time. For example, a negative Arctic Oscillation in November translates to a negative Arctic Oscillation in the following winter 68% of the time. The same goes for a positive AO. This is not good news for those wanting a negative Arctic Oscillation this winter, as the positive phase of the Arctic Oscillation tends to dampen prospects for cold weather. At this time, indications are that the AO may tend to be more positive than negative.

Sunspots
The October sunspot data was released in the last week, and it shows a worrying scenario for the upcoming winter. If we go by the acknowledgement that sunspot spikes precede a warm weather trend by 2-3 months, it's possible we see a solidly warm start to winter, possibly extending beyond December. This is currently to be determined as far as how the sunspots really impact the winter, but I personally don't like this new development as a winter weather fan.

What Hasn't Changed

Plains Outlook for a Snowy Winter
The Lezak Recurring Cycle continues to point to the Plains and Upper Midwest as being in line for a snowy winter this season. Multiple storm systems that have traversed through the region since October 1 indicate that the region of interest ought to have the advantage in the snow department this winter.

The Ocean Teleconnections
The Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, and ENSO indexes remain on track as forecasted: negative, positive and neutral, respectively.

The Quasi-Biennial Oscillation
Everything still on track for entry to Phase 7 by mid winter. Entry into that phase may be a tad earlier now, but the end half of winter should still see a full-blown Phase 7 QBO.

Practically everything else
The Final 2013-2014 Winter Forecast is looking fairly good at this point.

The warm start to winter still looks on, with a gradually cooler trend going on into winter. Expect a turbulent atmosphere/stratosphere in the end half of winter, as the changing QBO permits stratospheric warming events, and thus helps the chances for a negative Arctic Oscillation. Snow should favor the Plains this winter, with cold weather centered across the Plains, Midwest and Great Lakes. More to come as we press on into winter.

Andrew

November 17-20 Potential Winter Storm

There is a chance of a winter storm to impact the Plains and Midwest over the November 17-20 timeframe.

(From the post on November 6):

Shown above is the 12z GFS projection of 500 millibar height anomalies across the North Pacific, valid for November 10. If you look over by Japan, you will see a swath of negative height anomalies over that area. This is suggestive of a storm system in the area. As some of you may have seen on this blog and elsewhere, it has been discovered that troughing in East Asia tends to lead to a storm system and associated cold weather event in the East US roughly 6-10 days later, per Joe Renken. The image above is valid for November 10th, meaning we are looking at the November 16-20 timeframe for a potential cold weather event and winter storm.

On November 6, I discussed above how we should be watching the November 16-20 period for a winter storm due to a storm system in Japan, as is shown above. Well, the storm system is currently dropping down into Japan, and should go through the area in the next couple of days. This means the November 16-20 timeframe remains on track. And as of this morning, model guidance is beginning to catch on to this idea of a winter storm for someone in the East or, more likely, the Central US.

The ECMWF model shows three major players in its 240 hour 500mb vorticity forecast: a strong piece of energy in the Southwest, a piece of energy in south central Canada, and ridging along the West Coast of the United States. These three factors will influence where this potential storm system ends up, and how strong it may eventually become.

The prognosis is that a piece of energy will enter the Western US at around the same time another piece of energy drops down into the center of Canada. Now, the energy that will be hitting the US will ride up along the West Coast ridge and then drop down into the Rockies as it crawls along the Southwest to eventually push east. As it drops down from going over that ridge, it appears some of its energy will be torn off and push nearly due east, as the main bulk of the system drops down into New Mexico and Arizona. This torn off piece of energy will strengthen and interact with the energy in the middle of Canada to create the blue and green vorticity swirls you see on the Canadian/US border on the forecast image above.

The reason we want to watch this area of vorticity on the border is because it may do one of two things. It may: A) Pull the main body of energy north towards Canada, giving a snowstorm to the Plains and possibly the Upper Midwest. or, B) Have no interaction with the main body of energy, in which case the main body may prefer to move east-northeast and bring a snowstorm to the Midwest and Ohio Valley. The ECMWF does not go out past 240 hours, so we cannot see which solution it prefers (to me, it looks like the ECMWF may be leaning towards option A at this time, but I can't confirm that). However, we can see what the rival GFS model says.

Right off the bat, let's take note of how the GFS and ECMWF are very similar in their set-ups with this event for Hour 240. Both have ridging along the West Coast, both have the two pieces of energy I was discussing in the previous paragraphs, and both models have high pressure in the Southeast, something that will act to try and push the potential winter storm north into the Midwest or Plains rather than east into the Northeast.

The GFS model has the US/Canada border piece of energy further south than the ECMWF, and for that reason, the Southwest piece of energy (shown above in Texas and New Mexico) is weaker and more likely to push north into the Plains. I do believe that it is the US/Canadian border energy that will end up having the most say in where this storm goes, because if that energy is further south like the GFS shows, the storm system in question should push north and hit the Plains. But, if the Canadian system is weaker and more detached from the potential winter storm, we could see the storm affect the Midwest and Plains. And yes, if you're wondering, the Plains is currently in the best spot for this potential storm, but it's all still up in the air for another ~10 days.

An interesting piece to this puzzle is how the North Atlantic Oscillation is projected to evolve over this timeframe. The ECMWF model has the NAO changing phases twice between November 16 and November 21st. As you weather junkies may know, storm systems can be favored in the Northeast and along the East Coast when the NAO is changing phases. The model prognosis from both global guidance systems above would tell me that the storm system is unlikely to head east towards the Mid-Atlantic and such, but the changing NAO makes me want to keep an eye on that region around the November 16-21 timeframe in case something does develop. I'm not saying something will develop, but for all intents and purposes, I'd like to monitor projections over the East Coast in coming days if the projections for NAO changing phases continue.

Here's my current diagnosis on the situation. Bear in mind this is all preliminary, as we are still 240 hours away.

Andrew

November 14-16 Potential Major Winter Storm

There is a chance of a major winter storm in the Eastern US around the November 14-16 timeframe.

The current projection from the European ECMWF model shows a storm system to develop from the Southeast US before moving northeast and along the East Coast. Consequently, the storm system produces a major snow event, as the high-resolution snowfall forecast image shows below, courtesy of WeatherBell. The storm itself is produced as a significant high pressure system slips south from Canada. As the high pressure system pushes south, a storm system originates in the Southeast, and is pushed north and east as a result of this massive high pressure system. Let's take a look at that ECMWF snowfall forecast I told about a few sentences ago.

The ECMWF snowfall forecast is truly remarkable. A swath of accumulating snowfall extends from southern Mississippi to the northern border of Ohio, and from Maine to the Carolinas. Plowable snow is spread from the Northeast to the Mid-Atlantic, but it is West Virginia and the state of Virginia that gets hammered with as much as 36.6'' of snow, per the graphic above. Now, before we elaborate on this graphic further, please know that the chance of this graphic verifying on its own as is is **extremely** low. The chance of this storm happening is low as well, but realize that the 36'' is most likely not going to happen.

The American GFS model is much less enthusiastic with the event, bringing about plowable snow in an area from western Pennsylvania to North Carolina. Obviously this is not as exciting as the ECMWF model, but I'm more supportive for this solution than the European one. I'm not entirely gung-ho on this solution as is, but it's more realistic than the ECMWF projection.

So why don't I think this will be a huge storm? Well, we have to define a few things first.

It is likely that there will be a storm system in the Central or Eastern US during this timeframe. The image above gives an overview of the 500mb height contours and anomalies on the left, as well as cloud cover and sea level pressure contours/markings on the right. This image shows the Northern Hemisphere as of the time of publishing. Take a look over at Japan. If you look closely, you can see a spot of negative height anomalies over the East Asian nation. A rule of thumb in the long range world indicates that stormy times in East Asia correlate to a storm system in the Central/East US approximately 6-10 days later. With the negative height anomalies hitting Japan now, 6-10 days from today would put us in the November 13-17 timeframe, which is when the models project this winter storm to happen. That is a good thing for those of you wanting a snowstorm, but before you get excited, let's continue reading into this possible event.

If you're from the Northeast, you know that one of the most important indices to use in tracking the potential for a big winter storm is the North Atlantic Oscillation. In most cases, Northeast winter storms happen in a negative NAO. Winter storms can (and have) happen(ed) in a positive NAO, but the ratio of winter storms in the negative phase and positive phase decisively favors the negative NAO. So let's take a look at the GFS and ECMWF model forecasts for the NAO.

The GFS model projects the North Atlantic Oscillation to be positive during this timeframe, actually rising to a stronger positive stance as the potential storm unfolds. While there is truth to the idea that Northeast snowstorms can happen when the NAO is changing phases (i.e. positive to negative or vice versa), the NAO is just increasing its already-unfavorable attitude towards this potential snowstorm along the East Coast. I personally find that it would be difficult for this storm to move up the East Coast with such a strong positive NAO in place. Recall that the positive NAO allows a zonal flow (a flat jet stream, not wavy) to set up across North America. It would be pretty tough for a storm system to push north-northeast when the environment favors a west-to-east flow. Lucky for those in the Northeast, there will be a big Canadian high pressure system pushing into the Plains that will help out the chances for a snow event in the Northeast, and I will go more in-depth on that after this NAO discussion.

The European model isn't any better. It agrees with the GFS model in that the North Atlantic Oscillation will be strongly positive during this timeframe, and as I described above, the positive phase of the NAO greatly hampers efforts for this Northeast snowstorm, especially if the storm wants to go north-northeast per the ECMWF if the flow favors nothing close to that. There are always anomalies in the sense that the snowstorm may defy this positive NAO and dart north as a result of the huge high pressure system in the Plains trying to force the jet stream to bend around it, in which case the Northeast would have a decent chance at getting this potential snowstorm. However, the certainty in that proposal is much lower than the idea that the NAO will be moderately to strongly positive during this potential storm's timeframe.

Additionally, if you're one of the weather model junkies who prefer to live by the ensembles rather than the models themselves (a viewpoint that can be accurate when used correctly, but can be detrimental if over-trusted), don't argue the ECMWF and GFS NAO projections- the GFS ensembles and ECMWF ensembles confirm the positive NAO during the November 14-16 timeframe.

Now, the true wild card in those whole potential snow storm is Canada. Well, a Canadian high pressure system, to be exact.

The ECMWF and GFS both agree that a major Canadian high pressure system will slide down into the Plains in the day or so before this potential storm system. The image above, from the ECMWF model valid on November 12th, shows a 1045 millibar high pressure system in Nebraska. For those who aren't familiar with the millibar system, let me tell you that 1045 millibars defines a very strong high pressure system- not just any ol' high pressure system. There is the idea that some energy will ride the jet stream as it buckles south due to the high pressure system, well shown by the GFS model below:

You can clearly see the energy dropping south, right along the contour lines that show a steep ridging across the Western US, and then the downhill slope of contour lines in the Minnesota/Iowa area. This is the potential area of energy that would cause the potential winter storm, and its entrance into the US on the 12th bodes well with the East Asia correlation of a potential cold weather event/storm system between the 13th and 17th. Both the ECMWF and GFS agree on the entrance of this energy into the US around this timeframe, but the question is, how will the energy react when it encounters the rather-zonal flow along the East Coast (to which the positive NAO may be to blame)? Well, as the energy pushes southward, it is expected that some slight ridging will be produced on the waters east of the Southeast states. This would help northeast-ward movement of the storm system, like the ECMWF believes will eventually land it in the Northeast. However, if the ridging is too weak, the system may not move up the coast as eagerly. Or, if the ridging is too strong, it may stay further inland. Per the latest GFS and its ensemble system, the first option would come true, and the energy would meander off into the Atlantic, likely leaving some snow, but not a massive amount. I haven't seen a model call for due-north movement of the system in the event ridging is too strong- it appears to be the ECMWF's north-northeast movement vs. the GFS' eastward motion for this potential storm system.

Let's summarize all of this.

What we know

-There will most likely be a storm system in the Central/East US during the November 13-17 timeframe.

-A big Canadian high pressure system will drop down into the Plains to influence this potential storm system.

What we don't know

-The storm's track.

-The exact strength of high and low pressure systems in the Pacific and West US before and during the aforementioned timeframe.

So what do I expect?

I believe there is a chance of plowable snow (in this case, 2-6 inches) stretching from South Carolina to Massachusetts, but this is a low-confidence outlook. I do think there is a decent chance of snow falling in the outlined area- the question is how much. I prefer to play it safe at the moment and will go with the 2-6'' projection in the Plowable Snow zone, due to GFS/GEFS agreement on such an idea, but if the American models start to side with the pro-snowstorm ECMWF, you may very well see this outlook adjusted accordingly.

Andrew

November 16-20 Potential Cold Shot & Winter Storm

There is a possibility of a cold weather event and winter storm in during the November 16-20 timeframe.

Shown above is the 12z GFS projection of 500 millibar height anomalies across the North Pacific. If you look over by Japan, you will see a swath of negative height anomalies over that area. This is suggestive of a storm system in the area. As some of you may have seen on this blog and elsewhere, it has been discovered that troughing in East Asia tends to lead to a storm system and associated cold weather event in the East US roughly 6-10 days later, per Joe Renken. The image above is valid for November 10th, meaning we are looking at the November 16-20 timeframe for a potential cold weather event and winter storm.

As of now, there is no way to determine which areas may be hit by the potential storm system, and who may be affected by the cold weather. Per the weather pattern in the days leading up to the aforementioned timeframe of interest, I currently see the Plains at the best risk of this winter storm, mainly due to a rather strong high pressure system in the East US. However, as future model runs come out, the situation is bound to change. In the same sense, the potential areas affected are bound to change. This is a very fluid situation, and asking if your area may be affected will not yield any accurate answers, unfortunately.

Andrew

November 13-16 Potential Winter Storm

There is a very slight chance of a winter storm that may impact the Plains, Midwest and Northeast.

The European model had previously been showing a major snowstorm in the Plains, Midwest and Northeast from the November 13 to November 16th period. This came as the model projected a storm system to develop in the southern Plains that then moved north and east to spread snow across the aforementioned regions. The model has since lost the idea of the major storm, but with other guidance also showing the potential for snowfall in these regions in roughly the same idea (which we will discuss later), we are gong to look at the mid-level atmospheric set-up to determine if that forecast is even realistic.

The mid-level synopsis for this time frame from the 0z ECMWF shows a deep trough across the Plains, which in turn has provoked slight ridging in the East that gradually increases to a staunch high pressure system on the Maine border with Canada. This does have some merit- with model guidance in agreement on stormy weather prevailing over quiet weather on the West, the potential for high pressure ridging in the Southeast grows. That said, with the idea of a storm system arriving in the Plains, it wouldn't be difficult to imagine that the storm would then make a beeline for the Midwest and Plains, before possibly pushing north or east. This would only be possible if we see the colossal ridge in the Bering Sea break down in the day or two leading up to this projected storm.

Ensemble guidance confirms the widely-expected idea that a massive ridge will blossom in the Bering Sea in the next several days. When that happens, a very meridional (wavy) pattern will evolve throughout the eastern Pacific and North American regions. This huge ridge in the Bering Sea will lead to some decent troughing activity across the waters in the far northeast Pacific, with this resulting in ridging across the Rockies in North America.

Two or so days later, models agree that the ridge will start to flatten out across the northern Pacific, and it is here where the potential for this storm system arises. When that ridge flattens our, it is expected that the aforementioned troughing anomalies in the northeast Pacific combine with negative height anomalies in the Arctic to create an elongated negative height anomaly zone, and this would be expected to carry the storm system. As the elongated negative height anomaly zone moves east into the Rockies and Plains, previously-entrenched ridging over the Canadian Maritimes flexes its muscles once again, and provokes a situation akin to the one shown in the second image on this post.

Based on all of this information, and accounting for trends in the GFS and its ensemble set, I'm really unenthusiastic about this storm. While it technically can happen, and there is a chance, bear in mind that chance is very low. I do think there will be a chance for some snow during this timeframe as the pattern attempts to switch to a more winter-like pattern, but as of now, I'm not seeing a major winter storm in the forecast for the Plains, Midwest and Northeast.

Andrew