December 19-22 Significant Snowstorm & Ice Storm Update

This post will address the current situation of the model guidance, as well as what I think will be happening.

The ECMWF model, which previously dumped a wide plethora of snow in excess of one foot across the Lower Great Lakes, suddenly flipped over to the GFS' solution in an unexpected turn of events. The European model had been forecasting this solution for five consecutive runs until this afternoon, when it decided to take the snows further north in accordance with shifting the low pressure system itself further north. The GFS and GGEM had also taken this system further north with today's afternoon runs, meaning a consensus appears to be forming.

I have a few thoughts on this. For one, with a storm this strong, a northern shift to the storm was bound to occur, though one could argue it was made a while ago when the GFS came north after making its far-south forecast a few days ago. Strong storms naturally have the tendency to overachieve to the north, so to say, in that models may underestimate the northward motion of the storm. I find that to be a very plausible scenario, and it is possible this ends up being the final track to the storm.

Another possibility with this system is that it is not being handled correctly. This would arise due to the lack of this system being in the United States, where the radiosonde (instruments attached to the big weather balloons) can collect crucial data that then goes into the models, and enhances their forecast's credibility. Our system is not in the US yet- it is currently skirting the west coast of Canada. It is possible that the track will change again over the next 24-48 hours before it finally comes ashore. When it does come ashore, expect to see a model consensus quickly materialize, whether it be the one depicted above by the ECMWF, or a further south one.

One thing is for sure, however- this storm will be hauling loads of moisture northward. As the relative humidity forecast chart from the GFS shows, there will be immense amounts of moisture being pulled north for this storm. Regardless of where the storm ends up tracking, chances are good that someone will receive significant snow, while others receive a significant ice storm, and still others get flooding rains. This system will be one of the more powerful ones we have seen in recent years, and its impacts will not be as weak as some modeling systems have previously been predicting them to be.

Guidance does agree that there will be potentially significant icing involved with this storm. The GEM model above shows freezing rain accumulations for this storm in millimeters, and if you look closely at the pink dot on the right, it shows up as 100 millimeters of freezing rain. That is equivalent to just a few hairs under 4.00" of freezing rain. Now, I don't think this will be a 4.00" freezing rain event. The system is powerful enough, however, to produce a significant ice storm. We won't know specific accumulations for the freezing rain portion of the storm, but I would hazard a guess that over 1.00" of freezing rain is definitely within the realm of possibility.

Here's my last thought: I believe a southward shift is in the picture for this storm yet again. Why? Taking a look at model bias' yet again, as I have throughout this system, it was determined by the NCEP that energy in the Gulf of Alaska moves too slow across all models. Additionally, models have issues in not moving Arctic air and Arctic cold fronts south quickly enough to the east of the Rockies. Considering these two model bias', I do think there is wiggle room for another shift southward, and would not be surprised to see such a shift unfold. If we did see the energy in the Gulf of Alaska move faster than it is projected to (considered at this time to be a possibility), the system could very well return to what the ECMWF had previously been showing in terms of track, and possibly heavy snow as well. I'm not completely confident in these ensembles, so the chance of this happening is consequentially in question.

I would watch out for a southward model correction in future runs, in the event that we see the energy along the Canadian coast actually move faster than it is projected to. At the same time, however, the longer this new model consensus goes on for, the better chance it has of working out.

I'm not confident enough to release a second outlook, but here's a summary of my thoughts.
-We are looking at a significant storm system hitting a large part of the nation.
-A significant snow, ice and rain event is possible/probable with this storm system.
-There is potential for models to correct southward once again, though the degree of correction and probability of said correction is unknown at this time.

Andrew

December 20-23 Significant Winter Storm - First Outlook & Discussion

This is my first preliminary outlook for what is shaping up to be a significant winter storm over the upcoming weekend for a large swath of the country. A model discussion is included in today's post, and that's what we will begin with.

We're going to start off with the ECMWF model's projection, since it is the one that seems to be setting the trend for this event. In the image above, valid for Sunday morning, we see a strong low pressure system emerging over the southern Midwest and Ohio Valley. This chart from Meteocentre calculates the minimum central pressure to be at 996 millibars, making this a pretty strong storm. The intensity is no surprise, as I've been illustrating since December 11th that a very strong storm over East Asia will provide a base for a strong storm in the United States. The ECMWF has this system follow a track extending from the Southern Plains through southeast Missouri before continuing on through the Ohio Valley and eventually leaving the United States. I believe we will eventually see something very similar to this track, maybe shifted a bit north or south by the time the storm arrives. My reasoning?

The Earth System Research Laboratory (ESRL) puts out almost-daily teleconnection forecasts, and I have screenshotted two of them above. We see the forecast for the Pacific-North American index (PNA) on the left, with the North Atlantic Oscillation (NAO) forecast on the right. Matching up the index with the date on the bottom legends of each panel, we see that the PNA is projected to be negative (albeit rising) during this timeframe, with a strong positive NAO.

During a negative NAO, we tend to see big high pressure form across the Gulf of Alaska. Because we have a big rise in height anomalies over that body of water, there is a response of a dropping in height anomalies over the West Coast, meaning stormy weather forms in that region, as the graphic above from NCSU illustrates. Thanks to that stormy weather in the West, high pressure likes to form in the Southeast, and the two arrows (which illustrate the wind pattern in the area) combine over the Plains to show the storm track of systems during a negative PNA. Now usually, negative PNA storms like to go up into the Plains because the Southeast ridge is usually very strong. In this case, however, the positive NAO helps to keep the overall atmospheric pattern very progressive, meaning we don't see any persistent high or low pressure systems in any given area. As a result, that Southeast ridge is not given the opportunity to develop into a massive high pressure system. So, with this particular storm, I expect the system to move north due to that Southeast ridge (which will be slightly suppressed), and then take a track favoring snowfall from the east-central Plains through the Midwest and Lower Great Lakes and into a portion of the Ohio Valley, possibly even into the Northeast (though that is TBD).

The image above, from WeatherBell, shows mean sea level pressure anomaly forecasts from the ECMWF ensemble prediction system (EPS) across the nation for 144 hours, or 6 days out. We can clearly see the low pressure system in the Ohio Valley, and this is something the ECMWF Ensemble system has been hinting at for a while now. It has preferred this sort of track, and although I do not have snowfall figures from the ensemble mean, the similarity in track to the aforementioned 12z ECMWF run would tell me snowfall figures should be relatively similar. (For anyone interested, the ECMWF EPS Control snowfall forecast is directly below)

And now, for the moment you've all been waiting for, here is that 12z ECMWF snowfall forecast, using 10:1 ratios (where 10 inches of snow equals 1 inch of liquid)

Do I believe that this snowfall forecast will work out? Well, it's hard to tell. On one hand, the ECMWF does have a pretty good handle on this event to me in terms of consistency (compared to other models), and its idea for a significant snowfall jives well with the East Asian correlation saying that this will indeed be a significant system. On the other hand, we're still a ways away, meaning forecast models will most certainly change- the big question is if they change significantly, or just a bit. Based on the atmospheric set-up associated with this storm, I would think that this solution of snowfall placement would be within the realm of possibility.

Another possibility is that the storm actually goes further north, giving heavy snow to southern Wisconsin and a stripe of Michigan, as the most recent GEM model shows above. I believe this is a possibility, considering there shouldn't be a huge high pressure system in Canada to really suppress this storm to the south, but going against this idea would be the lack of a significant ridge in the Southeast to push it north, especially with the weakening -PNA (which really propels that Southeast ridge). In order to consider this solution a bit more, I would want to see more consistency with the GEM, as well as agreement from other modeling systems. However, judging by the overall pattern, as well as some model bias' I will discuss next, I'm not so sure that it's a real possibility.

Model guidance can be great, but it's not perfect. There are known bias' that have been outlined by various weather agencies, specifically the NCEP agency here in the US. These bias' should be able to help us determine what may happen that the models aren't clueing in on yet.

1. Tendency for models to hold energy in the Southwest for too long.
This is a rather well-known model bias, in that most guidance systems will end up keeping storm systems in the Southwest US for longer than they actually end up there. This affects our situation specifically in that solutions that are going for a further south projection for this system (see the GFS) may be incorrect. Should the energy eject from the Southwest quicker, it would seem to me that a more northern solution would be probable. I'm not exactly sure if that has been shed off by models like the ECMWF, GEM and ECMWF EPS yet, though it's just something to keep in mind.

2. Some models may close off low pressure systems too readily.
This is a model bias that really affects us here. Some medium range model guidance systems have the tendency to close off a low pressure system, meaning it will be cut off from the jet stream and just meander around until it is forced away by another low or high pressure system. In this case, model guidance generally agrees that our system will be closed off when it moves into the Southwest, and that's when model discrepancies begin to arise. Some guidance systems prefer to keep the system closed off for a while, which then results in a further south storm track, whereas other model systems don't keep the system closed off for so long, resulting in a northward track. In this case, I believe the GFS has kind of shed that bias it previously showed last week, and as a result we did see (and will probably continue to see) a northward movement in the storm track. As we move closer to the event, bear in mind these bias' become less and less involved in the models as they are shed away.

3. Arctic air will plunge southward quicker than models may indicate.
This is one that may or may not affect this system, as it's pretty apparent there will be precipitation mixing issues regardless of if this bias is in play. The NCEP indicates that medium and short range models will push cold air south to the lee of the Rockies slower than how it actually happens. In this case, one could argue that the cold air on the models is being underestimated, but as the cold air source in the Pacific (you weather junkies know it as the weakening negative East Pacific Oscillation) weakens during this storm system, I'm hesitant to count this bias as one to watch.

When I account for all the bias', the model trends, and some things I've been looking at over the past few days, I come up with this preliminary outlook.

To be quite honest, I'm feeling pretty good with the ECMWF operational and ECMWF EPS agreement. I feel that they do have the best handle on this system and the atmospheric pattern surrounding it, so my forecast was modeled after it. It should be noted that I did extend the significant snow area a bit north to account for any possible northward trends in this system. It should also be noted that there will be a sharp cutoff with snow amounts on both the northern and southern fringes, regardless of its track.

Rather than ask how your location looks, please look at the map- there really isn't any additional information I can provide you if you ask for a certain location.

Andrew

December 19-23 Potential Significant Snowstorm & Ice Storm

I'm feeling pretty confident that there will be a significant winter storm, composed of heavy snow and accumulating ice, between the December 19-23 period.

The following text & images are from yesterday's post on this system. The end of this copied portion will be denoted as (End of December 15th post).

A pretty strong storm system is expected to move across Japan in 48 hours, after dumping multiple storm systems over that area in the past few days. This storm system is looking healthy, as defined by the GFS ensemble mid-level height anomaly forecast above over Japan. As I have mentioned on this blog, there is a 6-10 day correlation between weather that occurs in East Asia, and weather that occurs in the United States. Thus, with this forecast image, we arrive at the December 13th date. Go ahead 6-10 days, and we find the potential storm timeframe of December 19th to 23rd. The reason I believe it may be significant is due to the strength of this system on the image above. Unlike the upcoming weekend storm, which saw only a moderate system in East Asia 6-10 days prior, the current East Asian projection is for a strong storm to hit Japan, and long range model guidance senses that this system will also be a strong one for the US. (End December 11 post).

The teleconnection forecast for the next little while from the Earth System Research Laboratory (ESRL) above shows projections for the Pacific-North American index (PNA), the North Atlantic Oscillation (NAO), the West Pacific Oscillation (WPO), and the East Pacific Oscillation (EPO). For this discussion, we will focus on the PNA and the NAO.

The forecast for the Pacific North American index is negative over the time period for this storm system, even bottoming out to its minimum during when I anticipate this storm system to strike. So what does the atmosphere look like during a negative PNA?

The image above is what is referred to as a negative Pacific-North American index phase (or -PNA for short). The negative PNA results from ridging in the Gulf of Alaska that then produces storminess/troughiness in the Western US. In response to that West US storminess, we then see the development of high pressure in the Southeast. The jet stream in this situation takes storms from the West and runs them north and east, typically delivering snow to the same areas that have been getting snow recently (think Plains, Midwest, Great Lakes regions). An interesting point of interest is how the two arrows on the image above (from NCSU) merge in the Plains. That means that, if the timing is just right, two storm systems could combine (phase) and form a stronger, single storm. History suggests storms that encounter phasing do become anomalously stronger thereafter, and can produce significant wintry precipitation. I'm not implying this will be a phasing situation, just something interesting.

The next item to discuss is the projected positive phase of the North Atlantic Oscillation. During the positive NAO, we see stormy weather over Greenland, which shifts the jet stream so the weather pattern is not conducive to those big high pressure systems you might sometimes see over the Bering Sea or even the Western US. The positive NAO pattern is what is called 'progressive', meaning no atmospheric feature really sticks around in any single area, because the atmosphere wants to keep this moving, so to speak. That said, previous forecasts for this storm had the system going north-northeast from the southern Plains into the Dakotas and Upper Midwest. Because of that progressive pattern, I'm really doubting we see such a spike northward. Will we see northward movement? Yes, because the -PNA will supply that ridging in the Southeast. However, the progressive nature of the positive NAO should limit any NNE or even due-north movement by this storm. I would watch out for the storm to move northeast, or even ENE.

This relative measure of predictability map, from the NCEP, gives us a glimpse at what atmospheric conditions are likely to be unfolding by an assortment of colors, defined in likelihood by the legend at the bottom. In this case, we see that blues have a single or low double-digit percent chance of verifying, while oranges define close to a 65% or better chance of verification. This map is valid on the evening of December 20th, roughly a day or two before this storm is projected to strike. There are three things we have to look at with this graphic.

The first item we'll discuss in this image is the ridging over the southern portion of the Gulf of Alaska. This ridging is encased in solid oranges right over the heart of the big arcing in the waters west of California and the coast, signaling high confidence that this ridge will be present. If that ridge is present, then is essentially guarantees the set-up I described above. Why? Well, that ridge in the waters off the West Coast then creates West US troughing, which provokes high pressure in the Southeast, and suddenly we have a classic negative PNA pattern.

Second, we see a swath of oranges extending from southern Canada into the Rockies. The troughing in the West from that negative PNA pattern tells us that the ensembles are sensing the trough to be our storm system in the December 19-23 timeframe. Like the Gulf of Alaska ridge, the oranges signify over a 60% confidence among the ensemble system with this storm system. Rising confidence among the ensembles for not only the storm itself, but for the NE Pacific ridge tells me that this storm is becoming even more likely.

Third, there is a wide body of oranges in the Southeast US. Going back to that negative PNA pattern, high pressure/ridging in the Southeast is expected, so it really isn't surprising that the ensemble set is going with a >60% chance of that ridge occurring. However, with the aforementioned progressive pattern thanks to the +NAO, it is unlikely that we see this ridge take over the East entirely. (End December 15 post). 

Now, I was running through model solutions and found something that makes me believe this will be a storm for the Midwest and Great Lakes, possibly not as far south as recent solutions have been indicating.

This screenshot shows mid-level vorticity forecasts from the GFS on the left and from the GEM on the right. Both are valid for Sunday, December 22 in the morning. Right off the bat, we notice significant differences among each model. The GFS on the left has closed off our impending storm system in the far Southwest, extending into Mexico, while the GEM has refrained from closing off the low and has instead propelled it eastward into the Plains and Midwest. As a result of the GFS' closed off solution, the storm system is cut off from the jet stream and meanders eastward into Mexico before finally being pushed northward again. It is this closed off low idea that creates the southern storm track (where snow is given to southern IL, IN, OH and into the Northeast), while the GEM's more progressive solution forms the northern track (snow falls across northern IL, IN, MI, OH into southern Ontario).

To be quite honest, I feel that the GEM has the right idea here, at least in not closing it off in the Southwest. In a recorded list of model bias', the NCEP agency notes that medium range models have a tendency to close off low pressure systems too readily. I feel that this is expressed in the GFS system on the left panel above, and in the latest ECMWF forecast. The GEM also closes off the low pressure system in the Southwest, but releases it from that closed position earlier, thus transferring the storm eastward quicker and going with the northern track. The difference between the GFS/ECMWF and the GEM is that the GFS/ECMWF hold the storm in the Southwest for a longer period of time than the GEM, and that leads me to the second model bias. I have mentioned on this blog that there is a bias that indicates models will hold storms in the Southwest for longer than they actually end up there. The GFS and ECMWF are perfect examples of this phenomenon (seen well in the GFS/GEM panel above), whereas the GEM does not keep the energy in the Southwest for such a long period. Based on those two bias', I do feel like the GEM has an accurate handle on this system.

And the interesting part is, it's not alone.

This dual-panel image shows mean sea level pressure (MSLP) values for Hour 168 from the GEM on the left, and the ECMWF Ensemble Prediction System (EPS) mean on the right. Thus, both images are valid for next Sunday morning. Notice the similar tracks in the MSLP values across the GEM and ECMWF EPS. Timing is a bit off, with the ECMWF EPS faster by a good 12 hours with this system moving into the Ohio Valley. However, the main point is evident in that the GEM and ECMWF EPS agree on this faster ejection of the system out of the Southwest. I feel that the GFS and ECMWF operational models are holding the energy in the Southwest for too long due to that bias, and while the GEM is also subjected to the same bias, it would appear that the model is circumventing it and is going with a quicker solution.

Here's the GEM snowfall and freezing rain projections, respectfully (Use Caution):

Measured in millimeters

I do think that one part of the model tendency to hold that energy in the Southwest might be due to the aforementioned negative PNA during this timeframe, but with the PNA gradually rising to positive territory around Christmas time, as well as the previously-discussed model bias', I doubt the storm would be able to stick around in the Southwest for as long as the ECMWF/GFS believe it will.

It's still a little early for any projected outlook due to model confusion, as well as a couple things I want to monitor over coming days to see if a southward shift shown in the GFS/ECMWF may be a valid possibility (though as I said, I'm not sold on it yet).

Andrew

December 19-23 Probable Significant Winter Storm

I would not be surprised to see a strong storm system traversing the nation over the December 19-23 period. We'll start off this analysis with a portion of the post from December 11.

A pretty strong storm system is expected to move across Japan in 48 hours, after dumping multiple storm systems over that area in the past few days. This storm system is looking healthy, as defined by the GFS ensemble mid-level height anomaly forecast above over Japan. As I have mentioned on this blog, there is a 6-10 day correlation between weather that occurs in East Asia, and weather that occurs in the United States. Thus, with this forecast image, we arrive at the December 13th date. Go ahead 6-10 days, and we find the potential storm timeframe of December 19th to 23rd. The reason I believe it may be significant is due to the strength of this system on the image above. Unlike the upcoming weekend storm, which saw only a moderate system in East Asia 6-10 days prior, the current East Asian projection is for a strong storm to hit Japan, and long range model guidance senses that this system will also be a strong one for the US. (End December 11 post).

The teleconnection forecast for the next little while from the Earth System Research Laboratory (ESRL) above shows projections for the Pacific-North American index (PNA), the North Atlantic Oscillation (NAO), the West Pacific Oscillation (WPO), and the East Pacific Oscillation (EPO). For this discussion, we will focus on the PNA and the NAO.

The forecast for the Pacific North American index is negative over the time period for this storm system, even bottoming out to its minimum during when I anticipate this storm system to strike. So what does the atmosphere look like during a negative PNA?

The image above is what is referred to as a negative Pacific-North American index phase (or -PNA for short). The negative PNA results from ridging in the Gulf of Alaska that then produces storminess/troughiness in the Western US. In response to that West US storminess, we then see the development of high pressure in the Southeast. The jet stream in this situation takes storms from the West and runs them north and east, typically delivering snow to the same areas that have been getting snow recently (think Plains, Midwest, Great Lakes regions). An interesting point of interest is how the two arrows on the image above (from NCSU) merge in the Plains. That means that, if the timing is just right, two storm systems could combine (phase) and form a stronger, single storm. History suggests storms that encounter phasing do become anomalously stronger thereafter, and can produce significant wintry precipitation. I'm not implying this will be a phasing situation, just something interesting.

The next item to discuss is the projected positive phase of the North Atlantic Oscillation. During the positive NAO, we see stormy weather over Greenland, which shifts the jet stream so the weather pattern is not conducive to those big high pressure systems you might sometimes see over the Bering Sea or even the Western US. The positive NAO pattern is what is called 'progressive', meaning no atmospheric feature really sticks around in any single area, because the atmosphere wants to keep this moving, so to speak. That said, previous forecasts for this storm had the system going north-northeast from the southern Plains into the Dakotas and Upper Midwest. Because of that progressive pattern, I'm really doubting we see such a spike northward. Will we see northward movement? Yes, because the -PNA will supply that ridging in the Southeast. However, the progressive nature of the positive NAO should limit any NNE or even due-north movement by this storm. I would watch out for the storm to move northeast, or even ENE.

This relative measure of predictability map, from the NCEP, gives us a glimpse at what atmospheric conditions are likely to be unfolding by an assortment of colors, defined in likelihood by the legend at the bottom. In this case, we see that blues have a single or low double-digit percent chance of verifying, while oranges define close to a 65% or better chance of verification. This map is valid on the evening of December 20th, roughly a day or two before this storm is projected to strike. There are three things we have to look at with this graphic.

The first item we'll discuss in this image is the ridging over the southern portion of the Gulf of Alaska. This ridging is encased in solid oranges right over the heart of the big arcing in the waters west of California and the coast, signaling high confidence that this ridge will be present. If that ridge is present, then is essentially guarantees the set-up I described above. Why? Well, that ridge in the waters off the West Coast then creates West US troughing, which provokes high pressure in the Southeast, and suddenly we have a classic negative PNA pattern.

Second, we see a swath of oranges extending from southern Canada into the Rockies. The troughing in the West from that negative PNA pattern tells us that the ensembles are sensing the trough to be our storm system in the December 19-23 timeframe. Like the Gulf of Alaska ridge, the oranges signify over a 60% confidence among the ensemble system with this storm system. Rising confidence among the ensembles for not only the storm itself, but for the NE Pacific ridge tells me that this storm is becoming even more likely.

Third, there is a wide body of oranges in the Southeast US. Going back to that negative PNA pattern, high pressure/ridging in the Southeast is expected, so it really isn't surprising that the ensemble set is going with a >60% chance of that ridge occurring. However, with the aforementioned progressive pattern thanks to the +NAO, it is unlikely that we see this ridge take over the East entirely.

Model forecasts aren't as consistent as I'd like them to be, but here's what the GEM and ECMWF models show for this timeframe. I picked them, because they seem to be following the progressive pattern, and do respect the Southeast ridge that is likely to be present in this timeframe.


The timing is a little off, though that could be attributed to the ECMWF tendency to keep energy in the Southwest a little too long, and the fact that we're still some time out from this event actually occurring. Nonetheless, other forecasts have the storm pushing more to the Southeast, and I'm really not so sure we'll see that happen. It would appear that the storm currently ongoing from the Midwest to the Northeast might be similar to this upcoming storm, as teleconnections will be nearly the same what they are now. Additionally, the negative PNA will be even stronger, and this would mean a more persistent Southeast ridge that would keep away any southern suppression of this upcoming storm system.

It's to be determined exactly where the storm will go, but you can kind of get an idea of my early thoughts from this post. I do expect this storm to be strong, and it will most likely have a wintry side with accumulating snowfall. The intensity is TBD, but confidence in the storm itself and the set-up surrounding the storm is rather high.

Andrew

Long Range Lookout: Brutally Cold December Continues into January

New data I've compiled over the past few weeks leads me to believe that the end half of December and on into January will be filled with some pretty cold weather.

This data came as a result of analyzing the stratosphere, and determining the placement of temperature anomalies. Using a 2-4 week gap between warming and cooling air masses in the stratosphere, something I like to call the Stratospheric Temperature Index (STI) was created. 

For some verification, take a look at this text from a post I made on December 1st:

Between October 30 and the first few days of November, the Central and East US experienced above normal temperatures in the upper stratosphere. This is displayed well in the Climate Prediction Center's reanalysis of the 30th in the image above. These few days between the end of October and the start of November also included slightly above normal stratospheric temperatures diving south from Canada, with below normal temperatures observed in the Pacific Northwest. Because the effects of stratospheric warmings are typically seen 2-4 weeks after the warming event, we took a look at surface temperatures from November 14-28 to see how well the surface temperatures matched up with the upper stratospheric temperature anomalies (note that this is a negative correlation relationship, meaning above-normal stratospheric temperatures will lead to cold surface temperatures, and vice versa).

Ground-level temperature verification from November 14th to November 28th, approximately 2-4 weeks after the height of this US upper stratospheric warming event, is nearly identical to the temperature anomalies experienced in the stratosphere. The regions that saw above normal stratospheric temperatures, including the Central and East US, as well as Canada, saw below normal temperatures during this timeframe. Similarly, the Pacific Northwest, which was bathed in slightly below normal upper stratospheric temperatures to kick off November, was included in slightly above normal surface temperatures from November 14th to November 28th. It would seem to me that the stratosphere had a direct involvement with these surface temperature anomalies, given how well the stratospheric and surface temperature anomalies line up. (End Dec. 1 post.)

Get the gist? Above normal temperature anomalies tend to lead to below normal temperature anomalies, and vice versa. So now, let's take a look at what's happening here, with the most recent verification.

This image from the 10 millibar region in the stratosphere shows significant below normal temperature anomalies across much of Asia into the Northern Pacific, with above normal temperature anomalies stretching from the United States into Western Europe, with another swath of warm temperatures in East Asia on November 28th, 2013. Let's see how surface temperatures for December 7-10 are showing up, as the 2-4 week verification window from November 28th of December 14-28 is upon us.

It's no coincidence that we saw strong above normal temperatures across the North Pacific in response to those below normal stratospheric anomalies in late November. The warm stratosphere in the United States shows up as below normal temperature anomalies, fitting in to the STI's definition. Also, note how Western Europe shows up as below normal, and even a portion of East Asia getting in on the cold weather. Can you see how the index is verifying?

Now, take a look at this image of upper stratospheric temperature anomalies for December 7th. We see a strong body of above normal anomalies in the United States, as well as Central/Eastern Europe into East Asia. Significantly below normal anomalies are observed across Canada, the North Pacific and far northeast Asia. 

If we take that verification window from the late November warming (December 14-28), we can expect that timeframe to be colder than normal in the US. With the current warming intensifying in the image immediately above, we can now expect continued cold weather in the December 21-January 4. Depending on how long the warming in the United States lasts, we could continue to see cold weather well into January. It is tough to tell the intensity of the cold, but based on verification stats, it appears clear that the United States should see at least some cold weather.

Andrew