Friday, January 11, 2013

Polar Vortex Could Collapse South into US

New signals are showing that the polar vortex could collapse south into the United States in the next 10-14 days.

Shown above is the 10 day forecast from the ECMWF ensemble prediction system, or just the EPS. The ensembles are forecasting 500 millibar height anomalies for this timeframe, where low pressure systems are shown in cool colors and high pressure formations are in warmer colors. The big green spot on the Canada-US border is the polar vortex itself- the low pressure entity which practically drives the Arctic to retain its cold powers. If this thing drops south like it did in 2009, cold to a very similar degree could be observed across parts of the nation.

Also key to this forecast is the presence of high pressure on the west coast of Canada and in the Pacific Northwest into the Southwest US. This is commonly known as the Pacific-North American (PNA) index, and is a driver of storm tracks and cold weather within the United States. When the PNA is in its negative phase, low pressure anomalies begin to build and persist in the West US (negative height anomalies, negative PNA), resulting in high pressure and warm air in the East US. Storms are then diverted into the Plains or way into the South. In the positive PNA, high pressure builds into the West, and low pressure evolves across the East, bringing higher potential for cold and snow to the central and east sections of the States. I find it very possible that the PNA could go positive after its been so negative recently- a huge low pressure system pushing south into the US means physics must respond with above normal height anomalies in the West US, and all of the sudden there's a positive PNA in the area.

The ECMWF Ensembles, despite the fact they are at the top of the most reliable models and ensembles of the world, are still prone to errors that strike the other global models, so do not take this as written in stone. It certainly is a good sign to see the ensembles agreeing on this- you need all the help you can get after last winter (even after last month)!

Andrew

11 comments:

Eric said...

Andrew, this is a good post, and it would be amazing to see this vortex come down into the US (just like 1984-85) and would verify my thoughts for the worst of winter to come later and for this to be comparable to 1984-85. (of course you've had the same forecast since at least early December, and I would have never saw this coming if you had not posted the northern hemisphere snowfall for October).

Eric said...

Here's what I said on weatheradvance, (just in case you didn't see it) on a few of my thoughts on this pattern. "Now, as far as what I’m seeing, I have not changed my ideas that I’ve had since early December for the worst of winter having yet to come, and a potentially brutal pattern to set up late Jan-Feb. This warmth we are seeing is not nearly as strong nor is at as widespread as what we saw in early December. Although some areas of the southeast will get quite warm and approach near record high temperatures, this warmth we are currently seeing is being induced by a few factors, including the MJO and the 25-30 day sunspot cycles. The 25-30 day sunspot cycles are partially to blame for this recent warmth, because the latest NOAA sunspot numbers and solar flux are among the highest observed in the entire solar cycle, and based on what was observed during the fall months, the downward part of the 25-30 day sunspot cycle correlated with cooler than normal conditions over the eastern US and caused the PNA to have a tendency to go into its negative state, so with the cycle very active, it is no wonder why we are seeing this sudden warm-up over the eastern US."

Eric said...

Also, this sudden increase in sunspots and solar flux may have an effect on the sudden strengthening of the MJO over the tropics, as more energy is received to earth’s surface, and considering that the greatest amount of sunlight energy is focused towards the tropics, this could possibly explain the sudden increase in rising motion over western Pacific, which has led to an increase in thunderstorms and a strengthening MJO. The MJO is currently over the western Pacific towards Octants 5 and 6, which favors warmth over much of the US, especially towards the eastern US, with any cool weather occurring towards the western US and sometimes into the Plains. However, this is what normally occurs, and what we are seeing in this instance is a displacement of the polar vortex (due to the stratospheric warming event which was caused by the Kelvin Wave over the Pacific in early-mid December) In fact, the current stratosphere temperatures at 10 and 50 millibars are at all time record highs for this date http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/05mb9065.gif interestingly, this would put this current warming event in comparison to what we saw in 1984-85. Now, there is concern from what I understand about the MJO remaining in the western Pacific as being shown by the GFS and its ensembles, and this would mean that warmth would try to fight against the impending cold coming from the displaced polar vortex. However, I have a few reasons why I don’t think this is to be believed. You have to understand that we are dealing with models here trying to forecast the MJO out to 2 weeks in advance, and lately, the verification of the models on MJO has been horrific, with the GFS and GFES two weeks ago having the MJO stay in the “igloo” or barely into Octant 4 and 5, of course, the MJO is now approaching Octant 6. Considering that the MJO is a tropical oscillation, in which the increased temperatures means a greater difference in energy per degree, and since we are also dealing with the tropical oceans (Oceans have 1000 x the heat capacity of air), this difference in energy is significantly amplified, and thus, this is why it is important to look at the tropics, before PNA, AO, NAO and other associated mid and high latitude oscillations because it is the tropics and the solar cycles which ultimately control the pattern, and these other oscillations are just indicators, not dictators of the pattern.

Eric said...

A tip I like to use when trying to predict MJO is to look at the temperature anomalies for the global tropical oceans, and by doing so, you can see there are large regions of colder and warmer than normal water over the tropics. It is over these areas with the highest anomalies from normal over the tropics that have a tendency to see the upward phase of the MJO go over that particular region of the globe. (link) http://weather.unisys.com/surface/sst_anom_new.gif This is the case because with warmer waters in place, it naturally warms the surrounding air, and since warmer air has a natural tendency to rise and force pressures to fall thanks to the air particles within warmer air moving more freely about, causing less air molecules to packed into the same amount of space. In our current situation, the MJO has moved quite quickly out of the Indian Ocean and towards the eastern Pacific, however, as time progresses the models show the MJO trying to hang around in the western Pacific, and if this occurred, it would be a warm pattern for the US. However, this does not make sense given that the Atlantic Ocean is deep into its warm AMO, and naturally, the MJO would have a tendency to force upward motion over the Atlantic due to the waters being warmer than normal, and with the eastern Pacific being colder than normal, it would seem that the models in this case trying to keep the MJO over the western Pacific, are having problems pushing the MJO towards the Atlantic because there is a a disconnect with the eastern Pacific being cooler than normal. (also this is the opposite of last year when the deep tropical Atlantic was cooler than normal) Now, when the MJO does move out of the western Pacific, we will have to keep a lookout for any potential Kelvin Waves, we saw less than a week ago, the SOI tried to crash negative, however the upward MJO pulse prevented this Kelvin Wave from strengthening because as the increase in thunderstorm activity occurred over the western Pacific, this lowered surface pressures, and with pressures over the eastern Pacific in relation being higher than normal, this induces a more east-west flow across the tropics where air from the region of naturally higher pressures over the eastern Pacific flows towards the region of general low pressure over the western Pacific. This east-west flow is associated with “normal” conditions over the Pacific, in which it follows the natural wind patterns over the tropics are induced by the Coriolis Effect. However, realizing that like the Kelvin Wave (which helped to lead to the current stratospheric warming event, and it’s the stratospheric warming event causing the polar vortex to become dislodged and is leading to the very cold weather being experienced over Asia) the MJO is one of the few things that can travel west-east in the tropics, it is very important to watch the MJO to help lookout for Kelvin Waves. My suspicion is that when the MJO starts to come towards the Atlantic, that with it backing off in the western Pacific forcing pressures to rise, and pressures lower towards the eastern Pacific, this could lead to the formation of a new Kelvin Wave where the air over the Pacific under this scenario naturally rushes west to east, just like the natural propagation of the Kelvin Wave. If this does happen, then I would not be too surprised to see a reinforcing shot of warmth into the already warm stratosphere, and this could mean even more deterioration of the polar vortex, helping to drive the NAO and AO considerably negative.

Eric said...

Also, with the 30 day sunspot cycles near their peak now, they should begin to drop off, and knowing the inverse correlation with sunspot cycles and PNA, the lower portion of the 30 day cycle that will come towards late January will lead to the PNA becoming positive, and with a strongly negative AO and NAO from the stratosphere, this would set-up a pattern in which it could get very cold and snowy over the US towards late January and February. Interestingly, the models agree with me in this instance, and they show the polar vortex currently located over extreme northern Canada becoming very displaced and heading towards southern Canada and the northern US in the longer ranges, and the reason the vortex will be coming south will be because of the increasing warming in the stratosphere over arctic, forcing the vortex to move southward to avoid complete collapse (like what happened in 1984-85), and with a strong gyre of low pressure forming over eastern Canada and the Canadian Maritimes, this will create a “fujiwhara” with the other strong region of low pressure (this strong region of low pressure being the polar vortex containing some of the coldest air in the northern hemisphere), and since the polar vortex is located to the northwest of this developing gyre of low pressure, this means that since fujiwhara of low pressure regions in the northern hemisphere goes in a counter-clockwise motion, this area of low pressure (polar vortex )would be forced to move southward in response. Interestingly, the timing on when this would occur would ironically be almost at the exact same time when the severe arctic outbreak in 1985 plunged into the US. (around and just after January 20th) This winter is not over by a long shot, and I will continue on my ideas for cold and the worst of winter to come towards late Jan-Feb.

ERN WX said...

Excellent work catching onto this!!! The SSW WILL HAVE SIGNIF impact on the wx over the next month. You got this one MUCH earlier than many and I say that proves why I support this site. Anyway, I see a decent amount of snow coming. That NAO could absolutely crash and the clippers are coming!!

Andrew said...

ERN WX: Always great to see you commenting, I hope your area gets some much-needed snow!

Andrew said...

Eric: Your analyses continue to amaze me. It's always great having people like you commenting on here to add more insight to this blog. I agree with that MJO theory- I haven't had a chance to look at that region, but I'll surely have to now!

Anonymous said...

@ Eric: Wow!!! Man, you must some kind of super professional!

Eric said...

@ Andrew
Thank you, and of course really could not have seen some of this without your posts and insight as well. I honestly have suspicions that the upward tick in the MJO over the western Pacific is being forced by the 25-30 day sunspot cycles because of how n increase in energy is received to earth's surface thanks to increasing solar activity. Considering that the warmer air has a greater difference in energy per degree than colder air and that the oceans having 1000x the heat capacity of air amplify this increase in solar activity would have the greatest effect (change in energy) over the equatorial Pacific because the Pacific is the largest ocean with the most energy and surface area over the tropical ocean on the globe, it really is a no-brainer in this case as to why the MJO suddenly strengthened deep into octants 5 and 6.

Anonymous said...

Does anyone have insight into the jet stream coming south into Iowa so we can get some more precip before winter is over!?! Does anyone think this will happen? Thanks