Monday, December 31, 2012

Stratosphere Analysis and Forecast - December 31, 2012

Model forecasts, specifically the ECMWF, continue to show increasingly-supportive signs for a polar vortex split. The ECMWF model shows two daughter vortices emerging 10 days out, one centered over northern Eurasia, and the other centered in Canada. High pressure separates the two. That is in the lower stratosphere. In the upper stratosphere, complete collapse of the polar vortex is being forecasted, with potential vorticity forecasts coming down to values that indicate the polar vortex is no longer supported in that stratospheric level, as forecasted below:

For those familiar with different levels of the stratosphere, this is the 10 millibar forecasted potential vorticity at Day 10. While there is a formidable area of potential vorticity (PV) values in western Europe, it's not nearly enough to support itself. Another extremely weak vortex is found in east Canada but again, it cannot support itself.

This is the isentropic leve; 475 K forecast for PV values at Day 10. Because the millibar equivalents are not listed, I believe this level is in the mid-lower portion of the stratosphere, meaning a vortex collapse here would be more significant than a collapse in the upper stratosphere. Anyhow, this forecast shows a full split has happened with the polar vortex, and two vortices have emerged. One is in far north Canada, and the other is an elongated vortex stretching across Eurasia. The second vortex is more significant because it is the dominant vortex in this situation. However, looking at the Day 7, 8 and 9 forecasts for this same level tells me the superior vortex appears to be on a weakening trend in this forecast. The perpetrator appears to be that dark blue finger of very low PV values pressing across the North Pole. This appears to be solidifying a split of both vortices, ensuring that the polar vortex is then more prone to collapse instead of being one vortex.

This zonal wind forecast for that Day 10 timeframe shows negative values from 70N - 90N, and positive anomalies across the rest of the board. Now, that huge negative anomaly signifies winds that go against the polar vortex. The presence of blue colors is bad for the polar vortex, so to see a swath of such a large and deep negative wind anomaly tells me the polar vortex is not going to catch a break anytime soon. I want to also point out that small finger of blues between the 30 millibar and 100 millibar areas on the far left hand part of the image. That is another wind-based phenomenon called the negative QBO. Without going too far into detail, the negative QBO creates a naturally-unfavorable situation for the polar vortex, because, once again, winds are going against the polar vortex.

This has significant implications as far as cold potential goes in January and February. The polar vortex will split, and that is the crucial step that then opens us to the potential of an overall collapse. Based on these zonal wind forecasts and PV forecasts, it looks like this split will be sticking around for a while. I am seeing potential for another warming in the next 2 weeks, but that remains to be seen.

And last but certainly not least, we need to wach the 10 millibar layer. Towards the end of the animation, you can see a sudden stratospheric warming blossom in the subcontinent of India. The angle of this warming tells me it may be trying to make a move towards the Arctic, but that certainly remains to be seen as the SSW occurs, surrounded by much below normal temperature anomalies. If this does propagate towards the Pole in the next week, late January-early February will only look colder.

In summary, my confidence is only growing in how the stratosphere will begin to buckle dramatically in the next 2-3 weeks. Model forecasts confirm my beliefs that all levels of the stratosphere will sustain heavy damage, and the upper stratosphere polar vortex looks like it will collapse. Very long range GFS model forecasts have been trending solidly with no polar vortex present in the 1mb, 2mb, 3mb and 5mb levels. The 7mb, 10mb and 20mb levels have their polar vortexes greatly displaced, and the lower stratosphere is experiencing splitting, not extreme displacement. Should this happen, the back end of winter will be cold. Not cold as in time to bring out the heavy jackets, cold as in highs in the negative digits (in places that do not usually experience such temperatures). If the vortex collapses... well, just remember what happened in January 1985:

Temperature Anomalies from January 20 - January 22, 1985


Eric said...

Great post Andrew, keep them coming. I find it very interesting that you referenced January 1985 (as I did in my post on December 9th, I guess great minds think alike then, lol.) I don't know if you saw this yet, but I suggest you to take a look at this video from meteorologist DT from, and let me know what you think about it. Here's the link

Eric said...

Here's what I thought about it, Ok, I was wondering who that was, I actually like DT and his forecasts are always interesting to me, but unlike him, I don’t tend to stare at models as much, I prefer to do forecasts the old-fashioned way through looking at the conditions at hand and history, and I only like to use the models after I’ve looked at these factors. I could actually see this occurring, with a period of warmth early-mid January, but this warm spell would not be as long nor as strong as what we observed in early December, I am not changing my thoughts at all for cold to attack the US later in winter especially towards late January and through February, of course I think the strengthening vortex over Canada that he mentions and the cold air loading over the arctic is merely a response to the larger scale drivers at hand, including the ongoing stratospheric warming event. The polar vortex though is not looking so good, not when you have split, competing vortices, and centers in different levels of the stratosphere are very misaligned, and like any region of low pressure, misaligned centers are not good for any strengthening or maintaining intensity of the vortex itself. The GFS and ECMWF stratosphere both shows cross-polar flow overwhelming the arctic, this is not a good sign for the vortex, and any ideas for a warm pattern over the US, because when you see winds like that in the stratosphere, what it does is it reduces the speed of the naturally westerly winds flowing in the stratosphere, or completely reverses them entirely) in the northern hemisphere, these naturally westerly winds induce cyclonic motion, however, with cross polar flow, these winds can change direction entirely and induce anticyclonic flow in the stratosphere. This anticyclonic flow is very detrimental to the vortex and can even result in complete collapse of the vortex itself, which is somewhat evident in the 10 millibar forecasts of the ECMWF and GFS. If this vortex collapse were to work its way down to the troposphere, then vast amounts of arctic air would be produced. In this instance, the reason I think the vortex over northern Canada tightens up is because as the stratospheric warming event occurs, this produces cold air at the surface, and in relation to the warmer air in the mid-latitudes, this sudden decrease in temperatures over the arctic can cause pressures to become very compact due to the vast difference in temperature, and with the AO and NAO going into their positive states, this is actually not a bad signal because these oscillations seem to be behaving this way because of the larger drivers at hand and the sudden increase in cold air"

Eric said...

Continued "This is exactly why I try not to just stare at these oscillations like PNA, AO, and NAO, like other meteorologists, I think you can sometimes get too caught up into them and this can lead to bad forecasts, and as I showed in my last post, even with the AO and NAO negative, and the PNA negative the pattern was warm over the US. Of course others blamed the PNA for this, but I clearly showed that these oscillations remained in their respective levels through the end of November, yet the pattern turned colder towards the end of December with all of these oscillations in their respective states. This proves that the AO, NAO, and PNA are not indicators of the pattern, they are merely resultants of the larger scale drivers like, 25-30 day sunspot cycles, northern hemisphere and siberian snowfall, ENSO, MJO, Kelvin waves, the polar vortex, and stratospheric warming events among other things. Going back to what we have at hand, as you know, over time, this cold air at the surface from the vortex in Canada will force pressures to rise due to colder air molecules moving less freely about, which makes them take up less space. Eventually these surface pressures rising may force a complete pressure flip and force the cold air to be released from these regions, and this is supported by the stratospheric warming event, which continues to intensify with time, and both the GFS and ECMWF show another shot of warming in the 10 millibar level to come towards the arctic from the northern Atlantic. The reason for this would go back to the anomalous region of low pressure sitting just south of Greenland and over eastern Canada, which was the same system that hit the eastern US and provided snowfall for areas near and just west of the I-95 corridor a few days ago. The strong region of low pressure in the troposphere, if persistent, can lead to a Rossby Wave feature, (essentially a very repetitive pattern of having a certain pressure pattern over a certain area of the globe), and this instance this persistent low pressure region (or even high pressure region) would produce large amounts of energy, in which can only be relieved by going upwards into the atmosphere. As more energy is produced by the tropospheric feature, this forces more energy upwards, and over time, this causes the upper troposphere and the stratosphere in which this energy is released into to warm-up. We saw a great example of this starting all the way back in November, with the persistent troughiness over western North America and ridging over the north Pacific (helping to create the -PNA) and in combination with the cold air residing near the surface forcing the layers above to expand and warm, these two factors likely significantly helped to lead to the observed and continued warming in the 100 millibar level over northwestern North America and extreme eastern Asia. "

Eric said...

What intrigues me about this situation is the fact that the models like the GFS and ECMWF pick-up on yet more warming to come into the arctic stratosphere from eastern Canada and the north Atlantic at the 10 millibar level. What is very concerning about this is, unlike the stratospheric warming present over northern Asia, this warming at the 10 millibar level has support underneath over northern North America at the 100 millibar level, with a plentiful amount of warming already present, this kind of situation allows for the warming at different levels of the stratosphere to vertically stack, and this makes it much easier to load cold air at the surface. This may be a good reason why in the longer ranges of the GFS and ECMWF we see a very strong polar vortex feature over northern Canada, and the increased strength of the vortex in the 500 millibar level itself may be a resultant of further stratospheric warming producing a lot of cold air at the surface, not an increase in the strength of the polar vortex itself in the stratosphere. With indications that the polar vortex severely weakened and even risking collapse in the stratosphere, it will be very hard for the vortex being shown at the 500 millibar level (which DT sites for his predictions) over northern Canada to hold the cold air in place without support from the stratosphere above. Thus, this is why I continue to think the pattern may turn brutally cold in late January and into February will turn colder for the US, and that any strengthening of the polar vortex at the 500 millibar level and the AO and NAO going positive are mere reactions to things like the stratospheric warming event and collapsing of the polar vortex in the stratosphere, and without support from the stratosphere above, the polar vortex in the troposphere will not have much support to hold the cold air to the north for too long, and I see it as only a matter of time before the cold air is released upon the US." In essence, I think that your ideas from earlier in December for a backloaded winter look like they are right on target, and this stratospheric warming event prediction looks really good as well.

Andrew said...

EXCELLENT analysis! I completely agree with you on how the AO/PNA/NAO are driven by other, larger-scale patterns. Patterns inside patterns. By the way, where do you blog these days? I haven't seen your (very popular) posts on weatheradvance recently.

Eric said...

@ Andrew Thank you, and if it wasn't for your outstanding analysis for stratospheric warming I may not have realized some of the things I just posted above, so I thank you so much for that. This website is also becoming quite popular as well, in many of my posts I make references to this website in which I get some of my ideas from and I've been able to get just about everyone at my site to also come here. I've also seen this website mentioned in Jeff Master's blog, in (one of the most popular weather websites on the globe), so that should tell you something, lol. I still do analysis under the comments section at under other forecaster's posts.
I have a subscription to weatherbell premium as well, and when I'm not making posts I'm usually commenting there or at other forecaster's blogs in my website, and then I also come here to look at your posts as well because I find them very interesting and well thought out. I have found weatherbell to be very useful of recent and Joe Bastardi and Joe D'Aleo have certainly helped me to realize new techniques and factors in forecasting that I've never considered before (like Kelvin Waves for ex.)
I do not usually make posts but once every 1-2 weeks because when I make my posts I provide a lot of information and make very specific forecasts, and go into very deep analysis of everything I see at hand. I usually plan on those ideas and forecasts to stick around through the duration of the 1-2 weeks until my next post, but also, like you I am somewhat crunched for time, so it limits the amount of posts I can make. I plan on having another one by early January, right now shooting for no later than January 7th, but that can easily change from now until then.

Anonymous said...

According to the table in the link below, 475K is considered to be about 100mb.