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.

Andrew

What I Expect For The End Of January

I have been talking a lot about the developing situation in the stratosphere, and have not really talked about what the end of January could be like. I think now's an appropriate time to do so.

The first thing to discuss is the stratosphere. As observed in the above animation, the month of January experienced two sudden stratospheric warmings- one centered over the Bering Sea, and the other (currently ongoing) centered over Canada. The ongoing SSW is the more significant warming between the two, with stronger and more widespread warming happening. With these sudden stratospheric warmings comes the movement of warm air. The basis of the SSW is anomalous warm air being forced up into the stratosphere, typically in response to some convection or torque-based event (there was a strong mountain torque event observed immediately prior to the ongoing SSW). With the forcing of this warm air is the weakening of the polar vortex, the driving force behind the Arctic Oscillation (AO), but that's a piece for later on. When you have large amounts of warm air being forced into the polar vortex, the vortex tends to go on a weakening trend. Depending on the strength and placement of the SSW, this weakening can be minor or catastrophic. This current warming looks to be enough to cause a split of the parent vortice into multiple daughter vortices.

In situations like these, I like to look at the polar vortex as an egg (bear with me on this one). When the SSW occurs and warm air is forced up, the polar vortex split can occur. Think of this as cracking the egg open, but not so far as to completely break it apart. The split of the vortex lets out a fair amount of cold air to lower latitudes but not the entire Arctic, similar to how a partial cracking of the egg leads to fair leakage of the inside contents but not the entire yolk.

Back to the relatonship of the SSW and anomalously cold air in the lower latitudes, there is typically a 1-3 week lag time. I prefer to use a 2-4 week lag time, because you're talking about thousands and thousands of feet to move air, and that takes time. Using that timeframe, and looking at the upcoming zonal-flow pattern ahead, I feel that the cold weather will be best felt beyond the third week of January, pretty much beyond January 20th. This will be of direct result from the ongoing sudden stratospheric warming, and the cold outbreak ought to last a good couple of weeks.

(Originally posted January 2) The GFS model is then pinpointing a third stratospheric warming in the long range, shown below:

10mb temperature at Hour 300.

10mb temperature at Hour 384.

Hour 384 is notorious for never verifying, but this warming forecast has been appearing on several GFS model forecasts, meaning the model appears more certain that this will actually happen, rather than not happen. The warming looks to originate over central Canada, right in the heart of a daughter vortice at that same 10 millibar level. That would only bring further weakening to the polar vortex/vortices.

If there is in fact a third sudden stratospheric warming (which I believe is definitely a possibility), there is no doubt that the amount of damage done to the polar vortex will lead to another, possibly stronger cold outbreak. The polar vortices can only sustain so much damage before another split into multiple vortices would result in a loss of the polar vortex altogether. That said, if a third SSW does occur, February would be quite a chilly month for many, as I have been hinting at for some time now.

Models also are tending to agree with the prospects for a sharp cold outbreak towards the end of January. The above forecast is of the CFS v2 long range model's weekly forecasts, with the top image valid for January 16 - January 22, and the bottom image valid for January 23 - January 29. In both images, we see sharp cold overpowering the nation, and significant warming ongoing in northern Canada. This significant warming bodes well for a ridge of high pressure in east Canada, something that could provoke a west-based negative NAO, which brings the party to the East Coast as far as cold and snow goes. However, considering the high variability between these weekly forecasts, I am hesitant to trust that negative NAO forecast. The cold has been trending on the CFS weeklies for a while now, so I am not as concerned for a bust potential in the cold as I am for the negative NAO.

My concern rests in the Madden-Julian Oscillation (MJO). This is a forecast chart of the MJO, with the forecasts in colors and observed conditions in a gray-ish color. Note how all members are in fair agreement with the MJO cycling into Phases 5-7 with increasing strength as time goes on. This does not bode well for cold weather in the East US. On the contrary, Phases 5-7 are very favorable for warm conditions across the nation. Now, if the forecasts were weaker with Phases 5-7 (closer to the center circle), I would not be as concerned. But alas, the models are in moderate strength with the dreaded phases of 5-7. The MJO only tries to reach pro-cold phases 8-2 by the beginning of February, and even then the MJO starts to die off.

We have the ball rolling very well here, as far as getting the cold down to the US. The stratosphere is experiencing a very formidable sudden stratospheric warming, and that will get the cold down to the surface. The question is, can the stratosphere overcome the MJO to get that cold air to come into the US rather than other parts of the world? My answer is yes. I have a good feeling we will have a good negative NAO setting up in mid to late January as the split in the stratosphere is reciprocated in the troposphere by pieces of the polar vortex being displaced away from the Arctic Circle and allowing high pressure to build in that area. Greenland would also be affected by high pressure formation, and the negative NAO would form. I buy more into an east-based negative NAO than a west-based negative NAO at this time.

Andrew

Announcements - January 2, 2013

Alright, I will be publishing a post tomorrow, indicating what I think will happen at the end of January. I've been discussing the stratosphere, it's time to discuss the surface. This will happen at 12:00 PM central time.

If time allows, work will begin on the Current Weather page.

Andrew

Multiple Stratospheric Warmings Confirm Polar Vortex Collapse Probable

I believe there is now solid evidence that a polar vortex collapse is probable in at least a few stratospheric levels in the next few weeks (for those wanting my definition of a collapse, see the last paragraph or two).

Part I: The First Warming
The first warming is ongoing, and has been ongoing for several days now. This sudden stratospheric warming is located in the mid-stratosphere at the 50 millibar level, as shown in the below animation:

The most intense warming is centered over northern Canada and the Arctic Circle, as shown by the highest maroon colored anomalies in the animation. This warming suggests even more warm air is being forced into the stratosphere, and the polar vortex should sustain damage from this. For those unfamiliar with the polar vortex, it is the low pressure system (vortex) that sits in the North Pole (polar) and holds cold air up. When the vortex is weakened, cold air tends to flow south. This is also known as the negative Arctic Oscillation.

We also use something called the EP Flux to measure what direction the 'wave' of this sudden stratospheric warming (SSW) is moving. Longer arrows with warmer colors tend to signal a stronger wave of this warm air. We can see how the SSW has evolved from the lower stratosphere to the upper stratosphere by December 31, the bottom right image. It is typical for the EP Flux to spike like this when an SSW occurs.

Part II: The Second Warming
After this first warming, it appears that we will be seeing a second warming in the next 10 days. Let's look at the zonal wind forecast from the ECMWF for Day 7:

In areas of negative zonal anomalies, you can find winds that favor the destruction of the polar vortex, while warm color winds tend to favor the formation and sustainment of the polar vortex. This is what the sudden stratospheric warming is- a change in winds. SSW's are indeed accompanied by these bursts of deep negative zonal wind anomalies which damages the polar vortex and can lead to cold outbreaks if the SSW is strong enough (which this one should be).

The two images above express 'waves' of geopotential heights. Wave 1 is on the top, and Wave 2 is on the bottom. In areas of warmer colors in either image, higher heights are observed, meaning high pressure has a tendency to form. In a similar situation, darker colors tend to indicate lower heights and thus low pressure areas form. Both images are forecast for Day 10. Let's start with Wave 1. Wave 1 will be going nuts over the SSW as it introduces high pressure anomalies to the upper stratosphere in response to the SSW. Again, going against the polar vortex (which is a low pressure system). By Day 10, because the First Warming is done, it will begin to die off. However, Wave 2 will begin to strengthen during that Day 10 timeframe, and this strengthening will occur through the upper and middle stratospheric levels, meaning that this second warming would theoretically have more of an impact across the whole stratosphere. In comparison, the Wave 1 had significant high pressure anomalies focused on the upper stratosphere.

This second warming should derail the polar vortex further to the point of a split, which we will discuss more on below.


Part III: The Split
By the time the second warming begins, the polar vortex has sustained enough damage that it must split into multiple pieces in order to sustain itself. This is shown in these ECMWF forecasts for different stratospheric levels:

100 millibar forecast for Day 10.

50 millibar forecast for Day 7.

5 millibar forecast for Day 10.

The 100mb level is closest to the troposphere (where we live), the 50mb layer defines the middle of the stratosphere, and the 5 millibar level is as far up the stratosphere I can get without putting up an image that resembles chaos, not a forecast.

I want to start with the 50 millibar layer. Think back to high-school biology for a moment. Recall that when cells divide, they originate from one parent cell and split into two daughter cells in order to make the object stronger (whether it be a cell wall (plant) or a cell membrane (animal)). Well, the polar vortex works similar, but not entirely the same. When the polar vortex is damaged, it will split into two vortices, called daughter vortices, in order to still maintain some control over cold air in the Arctic. When this split happens, it is not to strengthen itself like biology taught us, it is to keep itself alive, rather than experience a collapse in the single parent cell, resulting in chaos across the board. This 50mb layer clearly shows the split in progress by Day 7.

Now let's dart over to the other layers. The 5 millibar layer has a lot of things going on at once. In this case, there are actually three daughter vortices. One is located in Canada, another in western Europe, and the third vortice in Asia. They are all shown as several ovals tightened close to each other with decreasing numbers as you go toward the center of these ovals. The lowest pressure is identified with an 'L', in this case found over Canada. Also happening is a warming event, shown as the warmer colors in this image and happening over Europe and the Northeast US into the Canadian Maritimes. This will further weaken the vortices. High pressure has also built in over the Arctic in the absence of a single parent vortice, with the high pressure defined as an 'H'. The 100 millibar level does not show as severe a split or as severe a warming episode, mostly because the warming has been confined to the middle and upper stratosphere. However, if the geopotential Wave 2 forecast works out, that could change.

A few potential vorticity forecasts also show the split of the polar vortex:

Potential Vorticity at (roughly) 106 millibars at Day 10.

Potential Vorticity at (roughly) 50 millibars at Day 10.

Part IV: The Cold
There is roughly a 1-3 week lag time between a sudden stratospheric warming (SSW) and cold reaching the surface. Based on some research done, I feel that this timeframe should be more in the 2-4 week range this time around, which makes my expected arrival for the cold between January 22- January 27. This cold will persist for several days, especially if this second warming sticks around for a while. The weekly CFSv2 forecasts are showing such a sustained cold outbreak, as shown below in Week 3 (top) and Week 4 (bottom) temperature anomalies. ANOMALIES ARE IN KELVIN!

Look at all that blue- that's literally off the chart cold. The forecast is unable to produce any cooler anomalies, because the legend does not go any colder than that. The Week 4 forecast predicts temperature anomalies of 3.5 degrees Kelvin (roughly 6 degrees Fahrenheit) below normal across much of the nation. Significant warming in Canada suggests a continued weakening of the polar vortex may occur, along with blocking that may provoke a negative NAO, but that remains to be seen.

Part V: The Third Warming?
The GFS model is then pinpointing a third stratospheric warming in the long range, shown below:

10mb temperature at Hour 300.

10mb temperature at Hour 384.

Hour 384 is notorious for never verifying, but this warming forecast has been appearing on several GFS model forecasts, meaning the model appears more certain that this will actually happen, rather than not happen. The warming looks to originate over central Canada, right in the heart of a daughter vortice at that same 10 millibar level. That would only bring further weakening to the polar vortex/vortices and continues to confirm my suspicions of a collapse.

My definition of a collapse is as follows: "High pressure dominates the Arctic Circle, and any remaining polar vortices are weak and displaced to lower latitudes. A collapse is also believed to have happened if potential vorticity values are anomalously low." The definition of others' accounts of a collapse is different, but this is just what constitutes my posting of a probable collapse.

Things are looking up for a big cold outbreak in late January, an outbreak that could be sustained in the second and third warmings materialize and stick around for a while.

Andrew

Announcements - January 1, 2013

-Tomorrow, I will have a post basically confirming all suspicions of a polar vortex collapse at 12:00 PM central time. I'll describe the effects of cold as well.

-An update will be made to the Current Weather page tomorrow.

-I will attempt to make an update to the Models page.

Andrew