Monday, January 7, 2013

Severe Arctic Cold Could Mimic January 1985

Forecasts continue to be on track for massive cold to enter the central and eastern US after making its presence known in the West US in the long range. Shown above are 500 millibar height anomalies for Hour 240 of the ECMWF model run from Weatherbell.

I want to go into the high pressure ridge building over the Gulf of Alaska. This is a negative East Pacific Oscillation, or EPO. When a negative EPO sets up, cold air is then provoked to move into the central and eastern parts of the nation. It is thought of as one corner of a triangle of teleconnections that can bring cold air to the US. The second piece is the Arctic Oscillation, or AO. When the polar vortex is weak, cold air is not able to be held by the vortex and slips south from the Arctic. This is a negative Arctic Oscillation. Considering the polar vortex is going through heavy damage, the AO will be strongly negative and could bomb out to extreme negative values. The third item is the North Atlantic Oscillation (NAO). In the negative NAO, the jet stream buckles south to give parts of the nation cold weather. We see a battle ongoing between low pressure just south of Greenland (typical of a positive NAO) and high pressure to the north of Greenland (typical of a negative NAO). I think the NAO is definitely the wild card here, and could determine whether the cold stays in the Plains and Midwest (what I am thinking) or moves East into the Northeast and East Coast (which will happen, but may not be as cold).

Hour 216 of the GFS model.

An issue we are seeing on both the ECMWF and GFS model (image on the left from WeatherBell) for this event is the negative Pacific North American index, or PNA. In the negative PNA, low pressure builds over the West US and Rockies and provokes high pressure to build in the East. This whole cold outbreak will start with a negative PNA, which is why warm air will be maximized on the East Coast prior to this warm up, as the top ECMWF image is showing.





So we're seeing a tricky NAO and a bad PNA. Is this cold really going to happen??

YES. Both models have the polar vortex (yes, THE polar vortex) sliding into southern Canada and the north US. As it does so, the low pressure causing the negative PNA will also move east, bringing the unforgiving Arctic cold into the Plains and Midwest. The dreaded Southeast Ridge will then move out of the East Coast, allowing for some moderated (but still harsh) cold to bleed into that region.

Why am I so confident? The GFS has been giving a stellar performance with the stratosphere thus far, meaning it has a better handle than that of the ECMWF. If the GFS is to be believed, a negative NAO, negative AO and negative EPO will be in place when the cold breaks off and moves east in about 10-15 days. However, I think the ECMWF has a better handle on the North Atlantic Oscillation, hence my thinking that the strongest cold will be confined to the Plains and Midwest-Great Lakes.

Beyond January 20th, things become very murky, and I don't even want to go into what could happen after this initial wave of cold. We will have to wait a few more days to get a clearer picture of what happens post-January 20.

How could it mimic January 1985?


The top image shows the geopotential height at 30 millibars in the stratosphere for January 21, 1985, while the bottom image shows the ECMWF forecast at 30 millibars for 10 days out. Note the eerie similarities between the two images. We have the polar vortex in nearly the same spots for Canada/US border (I circled the two vortices in blue for the top image), and nearly the same spot for the other vortice in Eurasia. This similarity, combined with the negative EPO and negative AO could very well make January 20-25, 2013 be an extremely cold time not unlike January 20-22, 1985.

Andrew

14 comments:

armando said...

Wow this could be some serious winter occuring soon and I'm so excited! So Andrew if you have time and if it catches your attention could you make a post about a possible storm next week between i believe the 16-20? It's showing a nice ideal storm for the east coast and also the NAO is tanking so this could be an interesting setup! If you could that would be great if not it's totally fine! Thanks for the posts and keep them coming!

Anonymous said...

Would the cold areas get snow like detroit michigan

Eric said...

@ Andrew
Keep the posts coming Andrew, another good one here, I'm going to have a lot to live up to next week when my new post comes out, lol.

Eric said...

Andrew, here's something I said on my website and I figured it might interest you."In fact, just to prove my theory about Kelvin Waves correct, I want you to watch this animation (from the weathercentre) http://www.cpc.ncep.noaa.gov/products/intraseasonal/temp10anim.gif of the 10 millibar temperatures in the stratosphere. Now, we had the Kelvin Wave in the 2nd week of December, and notice towards the start of the animation the warmth that is setting up over the eastern Pacific. This is because the latent heat energy being released by the Kelvin Wave has nowhere to go but upwards in the atmosphere to counteract the excess heat energy, and considering warmer air rises, makes sense as to why we are seeing warming over the eastern Pacific in the stratosphere because of the Kelvin Wave. Now, I want you to follow that warming across the tropics, notice how it moves across the Atlantic, through Africa, and then once it hits Asia, the warmth explodes. Makes sense as to why the warming would suddenly occur over Asia because of the stronger snowpack near the surface, reflects solar radiation, cools the surrounding air, thus with colder air, air molecules take up less space and become more tightly packed. In doing so, you allow for more air molecules to be confined to a given space, thus it gives the air more “weight” and the pressures rise. This colder air near the surface and in the lower troposphere means that the specific layer in the atmosphere takes up less space, and in order to compensate, other levels of the atmosphere expand to fill the void. With the air expanding, it tends to warm as air molecules move more freely about, but with the addition of already warmed air from the Kelvin Wave propagating across the Atlantic, and through Africa, once this already warmed air reaches Asia it should warm substantially in response, and it is no wonder now as to why the warming event occurred in such a remarkable fashion over Asia towards late December."

Anonymous said...

Ok... I know I can get though this if only I had some idea when I could except spring..a little hint please? It can not be that far off can it?
bree

Anonymous said...

I sure hope there will be a snow storm or two to make this cold weather coming worth it! In the Great Lakes that is.

Anonymous said...

All right you have been beefing this up for weeks now, so can you actually give a *preliminary* forecast for where this will go? It's getting old, and it's raising questions as to whether or not its going into the US.

Andrew said...

Anonymous in Detroit: This is only about the cold, not the snow.

Andrew said...

Eric: Very interesting write-up! I'll be watching for that in the future!

Andrew said...

Anonymous at 7:57: This is still developing, but I said in the post it will start in the West and bleed east on the 20th and onward.

Anonymous said...

What kind of temperatures do you think we will see in north Texas?
Thanks

Anonymous said...

ok so it is going to get colder
will there be any snow with this

Anonymous said...

A few days ago I thought I seen where you were going to give an update on the snow for this weekend (storm track, snow amounts who might see it anything new) so will we see this update??????????

Anonymous said...

will the northern mid atlantic see any nor-easters and or strong storms? and will it be cold enough for snow, lots of snow?