Monday, December 31, 2012

Long Range Lookout: Storm Train Shuts off in Medium Range

It appears that the recent storm train that has brought heavy snow to many areas of the central and east US will be shutting off for a while. An example of the forecasted situation above is shown by the GFS Ensembles, with high pressure barricading storms from moving into the US from the Pacific. This barricade should hold for the next several days before it breaks and storm chances ramp up again.

This storm train breakdown will lead to warmer temperatures prevailing across much of the nation, including the Plains, Midwest and rest of the North US. It is expected temperatures will get as high as 10 degrees above normal, but a lack of warm fronts from storm systems means warm ups will not be extreme (i.e. 20 degrees above normal).

Again, this is only temporary, but it does bring a wake-up call that a continuous storm train can not and will not run on and on. At some point, the storms have to cease for a while. The worry is how long they will cease for.


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

Sunday, December 30, 2012

Polar Vortex Close To Collapse

As I have been emphasizing for days on end, the polar vortex is getting torn to shreds, and continues to look closer and closer to near-collapse with every model forecast. I will explain what is making it do so, and what it would take to make the vortex collapse.

These are two forecast images from the ECMWF model, with the top forecast showing the top layer of the stratosphere at 1 millibar, and the bottom forecast showing the lowest layer of the stratosphere at 100 millibars. Note how the 1 millibar layer shows high pressure covering the entire Arctic Circle, with the polar vortex now split into two vortices. This full split is much like cracking an egg- if you crack it into two, the yolk of the egg spills out. In this case, the cold air at the top of the stratosphere could flow down through the stratosphere, possibly even to the surface. As for the 100mb layer, high pressure is trying to build into the North Pole and attempting to split up the polar vortex, as seen in the 1mb layer. This is like partially cracking an egg- some yolk leaks out, but not all of it. Either way, it's progress.

This zonal wind forecast from the ECMWF, valid for 10 days out, shows very negative zonal wind anomalies in much of the stratosphere from 70N - 90N. These deep negative zonal anomalies signifies the creation of strong high pressure in the area, a.k.a. east winds. Sudden Stratospheric Warmings tend to initiate these different zonal wind values, and thus help to really hurt the polar vortex's strength. Seeing as how these easterly winds suddenly skyrocket in the entire stratosphere in the 10 day forecast, it's not all that far-fetched to continue to see severe damage inflicted upon the polar vortex at all levels.

These two graphs above show several things of importance. We'll start with the first set of image panels. The very top image shows an aqua-colored line of zonal winds at the 1 millibar level. We can see the sudden crash of the zonal winds at the 1mb layer, enhancing the forecast of zonal winds shown 3 images above this sentence. Let's now go to the bottom image of the first set of images. This shows EP-Flux, and essentially measures the strength at which warm air flows up into the stratosphere. The longer the arrow, the stronger the EP Flux and the more warm air wants to shoot into the stratosphere. Notice how it dies down again at the end of the forecast period, meaning the sudden stratospheric warming would stop.

The bottom set of images shows temperature forecasts. We want to pay attention to the first three images. They show the 10mb layer temperature for the first image, the 30mb temperature for the second image, and the 10mb/30mb temperature forecasts superimposed on each other. Now, we can see that both layers of the stratosphere warm nicely through the forecast period, a sign of the aforementioned sudden stratospheric warming (SSW). Even better for cold prospects (and polar vortex collapse pospects) later on is how this warming at the 10mb and 30mb layers does not crash back down to cold levels right after the warming, as is usually observed.

Some potential vorticity forecast images show a complete collapse of the vortex at what I assume to be the top of the stratosphere:

So all in all, the polar vortex is getting torn apart now, and will only get torn apart in the future even worse. A collapse of the vortex in the upper stratosphere appears likely, and it could only be a matter of time before the rest of the stratosphere starts experiencing big troubles as far as being able to maintain itself.

**Below info Updated at 2:30 PM**
The new 12z GFS forecast shows the polar vortex greatly displaced. Instead of being in the Arctic, it's all the way down in Japan! It appears another piece of the vortex may be off the coast of Europe. High pressure trapping the vortices south would theoretically deliver yet another crushing blow to the polar vortex, which I don't know will be able to recover fully in Jan-Feb.


Significant Cold Ahead For January-February

Significant cold is ahead for the months of January and February, especially late January into February. I'll explain what could cause this.

This chart of observed stratospheric temperatures for the years of 2011 and 2012 shows tat we have had two recent warming events, as shown in the red temperature line spikes on the far right of the graph. When these spikes occur, they are called Sudden Stratospheric Warmings, or SSW events. When an SSW occurs, warm air from lower levels of the atmosphere is forced up into the stratosphere. Because of the warm air being forced up, cold air originally in the stratosphere is displaced and forced down to fill the void left by the warm air now being pushed into the stratosphere. This is why we want SSW's to happen in the winter, so cold air can come down to the surface.

This ECMWF multi-panel graph forecast shows temperature forecasts for different latitudes. We see that the top 3 panels show significant and sudden warming of the upper stratosphere, including the 10mb and 30mb layers. This is a direct result of the sudden stratospheric warmings, and if these forecasts happen, it is certainly plausible that significant amounts of cold air will be displaced down into the troposphere (where we live). Even better news is how the two stratospheric layers do not directly cool down after the warming.

Even better news for cold air prospects is how the polar vortex is getting torn apart. For those unfamiliar with the polar vortex, it is the driving force behind the Arctic Oscillation and varies in its strengths. When it is weaker than normal, the polar vortex releases cold air down into the troposphere, much like the air displacement example shown above with the sudden stratospheric warming.

These two forecasts above of different isentropic layers show how decimated the polar vortex will be. The colors depict potential vorticity values, much like how high vorticity values signify low pressure systems at the tropospheric 500 millibar level. The two forecasts above show virtually no polar vortex to be found- the potential vorticity that IS present doesn't resemble a polar vortex in either of these two layers. This is exactly what I have been warning about- a polar vortex collapse. It seems to be happening in the upper stratosphere. If it propagates down to lower layers of the stratosphere, there's no telling what could happen.

Now, here's the big thing that will kick off the cold for mid-late January: CROSS POLAR FLOW.

The above image is for the lowest level of the stratosphere- the 100mb layer. I have outlined my best guess as to where the jet stream is. The plus sign signifies the North Pole. Using the outlined area, we see that the jet stream starts in Siberia, shoots north into the North Pole, and crashes south into the Plains, Great Lakes, Midwest, Ohio Valley and Northeast. The jet stream crossing the Polar region and then fleeing south into the US is called a cross polar flow and is commonly identified with the strongest cold air outbreaks in the US.

The stratospheric ECMWF is not the only model and atmospheric layer showing such a cross polar flow:

GGEM Ensembles showing Cross-Polar Flow in very long range

GFS Ensembles showing Cross-Polar Flow in very long range
Both the GFS ensembles and GGEM ensembles are showing cross-polar flow regimes setting up in the long range. This cross-polar flow is shown by high pressure pressing toward the North Pole, with low pressure then appearing across Canada and the US. Now, the GGEM Ensembles are indeed showing this cross-polar flow much better than the GFS ensembles. It is a very good sign to see two major ensemble systems showing cross-polar flow evolving, as well as the stratospheric ECMWF. If this happened, cold would invade the Lower 48 and would not be easily pushed out.

This is the zonal mean temperature forecast from the ECMWF model. I inserted an arrow into the 1mb - 5mb layers to signify what will happen now that this sudden stratospheric warming event is ongoing. That depression of light blue colors signifies cold air being forced down through the stratosphere in response to the sudden stratospheric warmings. Now, this air will warm as it pushes down through the stratosphere, but nonetheless, it is stratospheric air, meaning it will naturally still be colder than normal.

For the long range model forecasts, the CFS v2 monthly forecasts show a very cold January and February:


Saturday, December 29, 2012

Sudden Stratospheric Warming Begins





January 11-14 Potential Winter Storm




6z GFS forecast

12z GFS forecast

18z GFS forecast





Friday, December 28, 2012

Announcements - Dec. 28, 2012

Little to post about today, no big storms showing up in the long range. Today is focused on the Models page.

Thursday, December 27, 2012


It has come to my attention that I am being impersonated on my own weather blog.
I am furious at this. DO NOT believe ANYONE who says it is me unless it is linked to my blogger profile.


Sudden Stratospheric Warming About To Take Place






January 3-6 Potential Winter Storm

It looks like the potential is arising for a winter storm to hit the Midwest and Ohio Valley at the end of the first week of January. This possibility is being shown by the two major models (ECMWF and GFS) which we will review right now.

The above image is the ECMWF's 500mb height forecast for the evening of January 4th. Depressions in these isobars (lines of constant pressure) signify low pressure systems, while arcing formations depict high pressure systems. The ECMWF shows the storm system in the southern Midwest at this time. Typically, this would be a good snow maker for many in these two regions. However, the jet stream is aligned in something called a split flow pattern.

The split flow pattern involves high pressure stationed in the Pacific Northwest, leading to a literal split in the jet stream, and thus two branches of energy form: what I call the Southern Jet stream and the Northern Jet Stream. In this ECMWF Forecast, the Northern jet stream is stationed in Canada, and is shown by several isobars very close together. The Southern jet stream goes through Baja California, Mexico and the Southeast in a situation that could easily provoke severe weather. This split flow pattern keeps the cold too far north for these types of systems to access.

The GFS forecast for this storm system has the system further north, into the Midwest at this point. The GFS later brings the system down south into Kentucky like the ECMWF, but there are still big timing differences. The ECMWF and GFS do seem to be in good agreement as far as showing a common track, but the key thing is timing. It may just be 24 hours between the two forecasts, but that 24 hours can and will dramatically alter forecasts for this system, as demonstrated by these two models.

I think the ECMWF's forecast is more realistic. I find the split flow regime more likely at this point in time after a temporary Rex Block gives way.


Wednesday, December 26, 2012

Polar Vortex Breakdown Will Lead To Frigid January-February

Confidence is growing that the polar vortex will sustain enough damage to break down in some levels of the atmosphere and lead to a pretty darn cold January into February.

We'll start out with observations. Above is the observed temperatures in the 70mb layer of the stratosphere, known as one of the lower layers in the stratosphere. We are looking on the far right side of this picture to see current values. If we do so, we see that two warming events have already taken place. The first warming event brought temperatures well above normal in the 70mb layer, and there is an ongoing warming event taking place that is leading temperatures to skyrocket in the lower stratosphere.

[Animation of 50mb]

This animation of observed temperatures in the 50mb layer also shows such recent warming (for those unfamiliar with the millibar scale, lower numbers = higher height in the atmosphere). Both warming events previously described on the first graph are shown in this animation, with the first warming event propagating from East Asia into the North Pole. That warming event then died down and slipped back into East Asia. From there, that warm body of air moved across the North Pacific and is now in Canada, where it may be trying to make a move into the Arctic Circle. If such an event happens, this warming will become much more significant than the last.

The main subject of this post is something called the 'Polar Vortex', or PV for short. The Polar Vortex is a low pressure system stationed over the Arctic, with varying strengths. The PV is actually what drives the well-known Arctic Oscillation. When the vortex is weak, the AO is negative. When the vortex is strong, the AO is positive. We'll talk more about the AO later on. But it is important to note that the polar vortex is weakened when significant warming events, like the two shown above, happen.

Now, let's go back to the first chart. See how we are already well above normal for this time of year? That means that the polar vortex is theoretically weaker than normal at the moment. If that warming in Canada continues and/or strengthens, the polar vortex will only get weaker and weaker. As long as those above normal temperatures continue, the polar vortex is indeed vulnerable to collapse, if the right parameters come together.

There is something else used to see how the stratosphere is being impacted by warm air, and it is called the Eliassen-Palm Flux, or EP Flux for short. The EP Flux measures the strength by which air from the lower atmosphere is being forced into the stratosphere. Considering the word 'flux' means movement, one can think of the EP Flux as showing the strength of movement of warm air into the stratosphere. Shown above is an 8 day observation of the EP Flux. In recent days, we have seen the EP Flux strengthen, as the second warming event continues to hold its ground. Note the new presence of colorful arrows in the area above the number '10' on the lefthand side of the Dec. 24 image. This means that warm air is now penetrating the upper stratosphere, effectively infiltrating the entire stratosphere. This is a major blow to the polar vortex, as warm air is now pushing into the entire vortex, not just the lower part.

The ECMWF forecast for EP Flux is at the bottom of this multi-image forecast. Looking at that EP Flux, we see that the European model is forecasting the flux to rapidly strengthen as the New Year approaches. This would mean warm air from the troposphere would be shooting into the stratosphere at a rate more than triple the strength we saw with our first warming event in early December. That first warming event is shown as a cluster of arrows above the word '1DEC' in that same bottom image. Should such a forecast verify, it would be the highest EP Flux values we have seen this winter season, and would certainly induce very heavy stratospheric warming- even more than we have seen to this date. If any further warming occurs (and if the EP Flux forecast shown above verifies), we have a shot at breaking the warmest value in the 70mb stratosphere on that date (shown in the first graph as the top light gray line)- something that means chaos in the polar vortex.

Continuing with observations, we visit an index called 'Mountain Torque'. The Mountain Torque, also called MT, is a fairly challenging index to decipher. However, I have come to understand it as a component that can help warm the stratosphere and weaken the polar vortex. In high values of mountain torque, it is expected that the stratosphere will warm rapidly in a phenomenon called the Sudden Stratospheric Warming (SSW). (The Sudden Stratospheric Warming got its name due to the rate at how the stratosphere warms, hence the word 'Sudden'. There is also a weaker sudden warming event called a Major Stratospheric Warming event.) Considering the mountain torque values are at values not seen since late fall, I find it very plausible that the next 5-15 days will bring another good warming to the stratosphere, a crippling blow to the vortex as the current warming continues.

Now we get to the forecasts of what the models say will happen.

We start with the GFS model and what it says about warming in the stratosphere. Forecasters commonly use two types of graphs when dealing with the stratosphere: Temperature forecasts and pressure forecasts. The former option shows warmings in the atmosphere, the latter shows the strength of the polar vortex (remember, the polar vortex is a low pressure system just like ones we see in the US, just bigger and more permanent). We'll start with the temperatures. Below are 5 images of 5 layers of the stratosphere; I'll annotate each image appropriately.

1 millibar 10 day forecast

2 millibar 10 day forecast

5 millibar 10 day forecast

10 millibar 10 day forecast

30 millibar 10 day forecast
You might be wondering why you should care about a bunch of reds and blues and fancy colors. Well, in each of these images, significant warming in the form of very warm colors is shown next to very cool colors, a.k.a. the polar vortex. Anytime you see those reds and grays, that defines very warm air finally reaching the upper stratosphere.

Something very interesting I saw in those 5 images, something you may have noticed as well, is the steady westward progression of the warm colors with each image. If you can picture 3-dimensional things in your head, you may have thought of a spiral, in the sense of the warmest areas of each respective stratospheric level rotated as each image showed a lower level of the stratosphere. If you want to compare it to material objects, think of rotini pasta or how you get bubblegum from the gumball machine; how it goes down the spiral to your waiting hand.

That spiral analogy leads us into the next significant forecast piece- displacement. You may hear this word and think back to 8th grade chemistry and water displacement, or even high school, but this is a different displacement. This is the displacement of the polar vortex.

100 millibar 10 day temperature and pressure forecast

1 millibar 10 day temperature and pressure forecast
Shown above are two pressure and temperature forecasts from the ECMWF model. The letter 'L' defines the center of the polar vortex for each level in the atmosphere, and the letter 'W' shows the warmest values in each respective layer of the atmosphere. If you notice a plus symbol, that is the center of the Arctic, quite literally the North Pole. And if you happen to see the letter 'H', that symbolizes the highest pressure for that atmospheric level.

I said we were looking for displacement here, and that is what we will do. We are trying to find how far apart the letter 'L' is from the 1mb image to the 100mb image. If we look in the top image (100mb), we see that the polar vortex is centered just to the south of the North Pole, a.k.a. just north of Europe. The 1mb image on the bottom has the polar vortex just east of Greenland, and high pressure building in over Eurasia.
While this is not a classic example of extreme displacement, it is apparent that there is some good displacement. The top image shows two apparent centers of low pressure- one with the 'L' that I described in the above paragraph, and one not marked but still shown in the top right corner of the image in what appears to be East Asia. On the 1mb chart, high pressure has built in right over that second low pressure area that I told was in East Asia. As for the deepest centers of the polar vortex, they are relatively close to each other, meaning the displacement is not that extreme, but far enough apart for me to introduce my Jenga analogy:

Think of the game Jenga. You must try to take out pieces of the tower to get as many pieces out, but still have it standing. The more pieces you take out on one side, the more unstable that side becomes, and eventually the tower falls down because of the difference in stability of the tower (a.k.a. where more blocks are placed). In a similar situation, when you have the polar vortex far apart in different levels, like what is forecasted above, the polar vortex becomes more unstable and weakens, possibly to the point of collapse.

One more analogy for you: Think of the polar vortex like a cylinder full of cold air. If you cut the cylinder in half and move one half away from the other, the cold air will sink. That is exactly how the stratosphere. If you have displaced parts of the stratosphere, the cold air that is held in the polar vortex will be released and flow down into lower latitudes. If the PV is displaced enough, it may collapse altogether, leading to an icebox solution over parts of the world.

The GFS model shows a similar situation as far as that high pressure/low pressure difference in Asia, but has a lot more displacement in the actual polar vortex as shown below:

1mb 10 day pressure forecast

100mb 10 day pressure forecast
The GFS dislocates the polar vortex far away from itself in between these two levels, which theoretically would enhance the probabilities of a weaker polar vortex and thus higher potentials for a strong cold snap in January and February.

So, we have big warming in different levels of the atmosphere per the GFS big pressure differences in the polar vortex in the GFS, as well as good displacement of the vortex in the ECMWF. But there is something else showing up in the GFS- complete collapse of the upper stratosphere polar vortex.

1mb 384 hour pressure forecast
5mb 384 hour pressure forecast
10mb 384 hour pressure forecast
This is where you will need to read these images closely. We'll start with the top image at the 1mb level. In this top image, we see a large circle covering much of the Arctic. If you read closely, you will see that the numbers go up as the lines get smaller, meaning that this is a gigantic high pressure system. The polar vortex has collapsed in the 1mb layer at Hour 384! The 5mb layer shows a big high pressure system over the Bering Sea splitting up the polar vortex into two pieces, and a similar forecast resides in the 10mb image.

You weather aficionados are most likely wondering why I'm showing forecasts at Hour 384, the longest of the the long range, and the high point for forecast failure rates. The reason is simple: Trends. I went back across several GFS runs for the 1mb forecast and found that the high pressure system was still covering the Arctic in as many as 5 other forecasts. That said, my faith in this forecast increases dramatically, and, while it's still quite a ways out, I am encouraged by this forecast of a polar vortex collapse in the very upper stratosphere.

Remember how I said the polar vortex is the driving force behind the Arctic Oscillation? Let's keep that front and center. This is a multi-model (and ensemble) forecast of the Arctic Oscillation. In this forecast, we see that the GFS, GFS Ensembles and GGEM Ensembles project the AO to be in the positive range come the 2nd week of January. Based on all the evidence I reviewed above, do you think that will actually happen?

This 8-10 day 500mb height anomaly forecast from the ECMWF (left) and GFS (right) shows no striking presence of a positive Arctic Oscillation, which would be shown as below normal height anomalies across the Arctic Circle. While we do see some low pressure anomalies creeping into the North Pole, nothing defined is showing up, meaning I believe this positive AO forecast is bogus. Considering the warming already happening, the warming forecast to happen, and, potentially, the collapse of the upper stratospheric polar vortex, I have a hard time believing the models are correct with a +AO in the future.

In summary:
-Significant warming is already ongoing in the stratosphere.
-EP Flux values are now pushing warm air into the entire stratosphere.
-EP Flux forecasts show dramatic and significant warm air being forced into the stratosphere.
-Mountain torque highlights more stratospheric warming in the future.
-Model forecasts support heavy damage being sustained to the polar vortex.
-The positive AO forecast does not look correct in my opinion.

All in all, what I have described here today bodes well for a cold episode that may span the months of January and February. If the polar vortex has a collapse, severe cold could very well overtake the nation. Prepare for cold times ahead.