Friday, January 4, 2013

Arctic Trifecta Could Lead To Brutal January-February

It is becoming increasingly apparent that three big atmospheric factors will have to combine in an Arctic Trifecta to make for a brutal end of January into February.

Part I: The Stratosphere

The stratosphere is one of the three big factors needed for a brutal back-end winter, as it is where the polar vortex is based. If we want cold weather, we need that polar vortex to break down.

Observed temperatures are shown on the two graphs above, with the 1 millibar level being shown in the top image, and the 10 millibar level temperatures depicted on the bottom image. These two images show a spike in temperatures in recent days, and this is in response to the big sudden stratospheric warming (SSW) that is in India and spreading across much of Asia as an extreme SSW. The 50 millibar ongoing SSW has yet to be recognized at that level. Nonetheless, any progress is good progress as we will now see a round of damage be inflicted upon the polar vortex. This is the first warming of three that I am concerned about as far as implications on the polar vortex go, so we will move right along to the second warming.

The second warming event should take place in the next two weeks, and the ECMWF model is pinpointing its appearance in the 9-10 day range. Shown above is a forecast image of temperatures across the stratosphere and troposphere, the latter layer shown in the bottom part of the image. We want to pay attention to the upper stratosphere in this case. We see significant warm air anomalies prevalent in the upper stratosphere between 70 N and 90 N. A look at Days 6-8 forecasts reveals this warm air intrusion is only beginning on Day 10, and such an intrusion is signifying that, yes, the second warming event should be ongoing through Days 9-12. I cannot be confident on that timeframe, considering the ECMWF only goes as far out as Day 10. Any way you put it, this significant warming in the upper stratosphere bodes well for extensive damage being put on the polar vortex.

The negative zonal wind anomalies at the top of the right hand corner also suggest a second warming event is in the making. Notice the now-weakened polar vortex between 30N and 50N. This will only get weaker with this second warming, if the second warming turns out to be near the significance that the currently-ongoing one is having.

Skyrocketing heat flux forecast values and a downward-propagating geopotential Wave 2 forecast enhance the chances of a good second warming in the stratosphere:
Geopotential Wave 2 Day 10 forecast.

Heat Flux Day 10 Forecast.
If the geopotential Wave 2 does propagate downwards with its higher heights (high pressure, observed by the warmer colors in the top image), one can expect lower stratosphere disruption in the polar vortex. It doesn't matter if the polar vortex is gone in the stratosphere- it only matters if the troposphere feels the effects, and that's what we need right now to make sure this trifecta can happen. As far as the heat flux goes, it is nowhere as strong as the ongoing SSW, but again, progress is progress, and after a fairly dismal December, we will need all the help we can get.

And then there's the chance for a third warming. This third warming, if it were to happen, would come at a time when the polar vortex has already been split into multiple pieces and absolutely decimated on all levels as far as strength goes. Suppression south is beginning to occur with the remaining polar vortex pieces, meaning Eurasia and North America would begin to feel an Arctic chill.

This suppression is well observed in this long range GFS forecast, which shows the polar vortex entering the Great Lakes region. Temperatures as low as -30 are observed in the upper Midwest, and cities like Chicago, Quad Cities and Gary would experience temperatures well below 0. This is just one of many possibilities facing us if this third warming event comes to fruition.

I should note that the lower stratosphere is predicted to have a good piece of the polar vortex in southern Canada during this same timeframe, meaning that the stratospheric effects are propagating down to the surface. Cold air would certainly be in order for much of Canada and possibly the US if the polar vortex made its way close to the US. If it ENTERED the US, record-breaking cold is more than possible, but I want to wait several more days to let the GFS sort itself and any forecast errors out.

Part II: The Cross-Polar Flow

There is an atmospheric pattern called the Cross-polar flow that is widely acknowledged as the pattern that brings the coldest air to the US the easiest. The term originates from the way a strong ridge of high pressure builds into the Gulf of Alaska to the point that the jet stream actually has to cross the North Pole to get north of the high pressure in the Gulf of Alaska. From there, the jet stream collapses south into the Rocky Mountains, transporting frigid air as it goes. We are seeing good signs of the cross-polar flow setting up in the long range.

For example, hour 288 of the GFS control model run shows a fantastic cross-polar flow ongoing, with extreme ridging happening from the Gulf of Alaska to the Arctic Circle. The jet stream is then observed shooting south into the West US, with significant cold air following the jet stream. This pattern also opens the door for a McFarland signature, which is the death-bringer to crops everywhere near the Rio Grande. As observed by McFarland, an atmospheric pattern will set up in which high pressure will build in the East, and low pressure in the West. A severe arctic outbreak will press east across the nation, and anomalous high pressure will build in its wake, holding the nation in a deadly Arctic outbreak. This forecast certainly shows some McFarland characteristics, but for now we will just focus on the cross-polar flow.

The ECMWF model and ECMWF Ensembles also try to build some cross-polar flow, albeit to a much weaker degree than the GFS control:

ECMWF 500mb height anomaly for Day 10.

ECMWF ENS 500mb height anomaly for Day 10.
Don't immediately bet against the GFS control. The ECMWF Ensembles naturally have to be weaker than the individual model forecasts because the ensembles are just that- ensembles. They are composed of multiple forecasts and are only showing an average of the members' forecasts. It is entirely plausible that 50 of the 51 ECMWF ensemble members show extreme Gulf of Alaska ridging, but one member shows record-breaking low pressure anomalies in the Gulf of Alaska. While that's most likely not happening, just remember this is an average of dozens of individual forecasts.

Part III: The Teleconnections

The third and final part of this Arctic Trifecta is the teleconnections, particularly the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). In the negative phase of the NAO, the jet stream buckles south to bring cold and storm systems to the Northeast, while the negative AO brings about a cold weather pattern across the nation. Both of these oscillations ca be detected by models, so let's see what they show.

Let's bring back the ECMWF Ensemble image for a moment. This is still valid at Day 10. We can clearly see a strong negative NAO and AO. How? High pressure is building over Greenland in this forecast. The negative NAO is achieved by seeing high pressure build over that land mass, in turn bringing about cold weather to the Northeast. The negative Arctic Oscillation is then found by the presence of multiple high pressure systems dominating the Arctic Circle, the typical domain of the AO. The negative AO and negative NAO would typically combine to bring cold air to the East in such a situation, but as you can see, high pressure is building across the East Coast. Why? The dreaded negative Pacific North American index, or negative PNA. The negative PNA, while a common trait of cross-polar flow and the McFarland signature, causes high pressure (and thus warm air) to build across the East US. We will need to see an equally strong negative NAO or a weakened negative PNA to see that high pressure get out of the East Coast. Eventually, by the end of January, this should very well happen.

This Arctic Trifecta can work out very easily, I have no doubt about that. The question is, can the negative PNA turn into more of a McFarland signature to push the cold east, or will it persist in the West? If persistance occurs, cold prospects are dimmed. However, the breakdown of the polar vortex practically assures that some degree of colder weather will be forced into the US- it's how cold that is the question.



Anonymous said...

Hey there Andrew, make your call and stick with it. Your previous posts made it sound like this collapse was a sure thing. You're giving yourself an out with these 3 conditions needing to take place. And what about that big storm with 20" snow for Ohio in mid Jan? What happened to that one, did it just vanish?

Andrew said...

I never have you such a bad attitude, please give me the same respect I give you. As for the collapse, it is a sure thing. This concerns cold getting into the US, not the polar vortex. I never told of a 20" snowstorm; you are mistaken. This 'out' you speak of is not an out- it's the uncertainty that comes with forecasting in the long range.

Anonymous said...

Andrew, I love your forecasts & look forward to each update! (Even though I hate winter) Keep em coming!
I pass your web- site on to everybody I know & they love ya too!! Keep up the great work!
(Can’t wait to see spring!!)

Anonymous said...

Um, yes you did mention something about 20" equivalent back on the 1st. Go back and re-read your post from that day. Good to see that you actually respond when you're questioned. By the way, what exactly were you trying to say in your first sentence? It didn't make any sense. (I never have you such...)??

Anonymous said...

Your work is fascinating to me Andrew, valuable too, many thanks. Please ignore the people who don't realize how difficult at 15 day forecast is!

Andrew said...

Anonymous at 9:05: Okay, stop being so arrogant. And about the 20" post, I never said it would actually happen- it's a given that such a long range forecast doesn't happen as shown.

Andrew said...

Bree: Thanks for passing it along- very happy you like the posts! There are many more to come!

Anonymous said...

Pointing out what a model is showing 11 days in advance (1.95 inches of precipitation = 20 inches of snow) isn't a forecast. It is explaining what that model run was showing at that time.
And it is amusing that the first anonymous took today's post as "an out". That makes little sense. I guess you can't please them all.

Art Vandelay said...

Andrew where are you getting this information, surely you can not conjor up such a detailed analysis yourself

Andrew said...

Art: Insult me all you want, I honestly don't care what you think of me. I'm putting this up here to show others how low you can stoop.

Please move on from this blog, I don't want to have you making this a bad place to be.

Anonymous said...

If this happens as the way you explain it may happen, what do have to say the effect will be for the deep south such as south east Texas Louisiana and Florida. You only speak of west and east,thank you love your blog have shared it on YouTube. Dont forget to broadcast yourself :)

Jack Frost said...

If you people can't give the respect to this guy (Andrew) that he deserves, do as he says and move on.

Honestly, he obviously works very hard providing us with his analysis and insight and only to get slagged off by you bone heads.

Andrew - keep up the great, I for one appreciate it!

Anonymous said...

Pretty simple if you don't care for this website don't log in. Also, there is no one that accurately can predict the weather all the time.

Anonymous said...

Thanks Andrew, we love big weather at our house and love to follow your posts. The Shenandoah Valley (SV) is a hard place to predict weather,we are told this by our TV weather people daily. Your blog gives us more detail, which is helpful. I too have passed your blog on to other weather fanatics and they love it! Keep them coming. If any big weather is heading toward the SV please tell.

Anonymous said...

Andrew, as hard as it may be not to get annoyed with posters who hold you to every word they either don't fully understand the complexity of weather or if they do have a very narrow approach to forecasting long term or forecasting in general. If I went to bed waiting for that big 2 ft snowstorm I was hearing about and get partly sunny I certainly did't send a hit squad out on the weatherman.

I find your forecasts very interesting and the detail you place into them as educational. Weather can change on a dime, people who don't understand that maybe are frustrated about our winters lately being so different from what we are accustomed to.

Keep up the good work, by the way, although I have my gripes lately with the Weather Channel especially since they were bought out by NBC but they have been talking about the breakdown of the polar vortex as well today, but not nearly as in depth and gave a very so so implication of its possible result.

Keep up the good work I look forward to your posts.

Anonymous said...

Art...your comment shows that you know nothing about weather. You're just here to criticize. Weather troll.

Anonymous said...

I personally don't understand why you recieve such criticizm, Andrew.
I always enjoy reading your posts, but never remember when you ever called a model run a true forecast unless it is less than a week out, and even then, I don't ever recall you ever making any guarantees about any model panning out, in fact, the only guarantee I have ever heard come out of your mouth is that this winter would not be a repeat of last year, and you were spot on about that, this year has been nothing like last winter.
So don't mind those fools who criticize you and your work, because many of us here support you, and will back you up anytime, so, you always have my vote, from Palmer Lake, Colorado.

Andrew said...

Jack: Thank you very much for the support!

Anonymous from SV: Thank you for passing it along- I just published a new post concerning the next chances for snow.

Anonymous from Palmer Lake: Your support is very much appreciated- I take everyone's support personally.

Anonymous said...

Your interpretation of the -NAO is incorrect. The East Coast/Northeast need a West based -NAO with heights above normal in the Baffin Island/Davis Strait region while an East based -NAO favors the areas between the Rockies and Appalachians. Surely you have seen this on forums.

Andrew said...

Anonymous at 5:20: I was providing a more broad-brush definition of the NAO, which in itself is typically biased to the Northeast for its tendency to provide Nor'easters. But yes, there is a substantial difference between west and east based negative NAO.

Anonymous said...

Two more days down since this post? How is it progressing? Delayed a bit?

Anonymous said...

Thanks for the effort you put into these forecasters Andrew, why you get so much criticism is beyond me... I would like to see them try to interpret all the models etc, and put it into a forecast!