Friday, February 1, 2013

February 10-12 Potential Winter Storm

There does appear to be potential for a winter storm from the 10th of February to the 12th. Let's dive right in.

Model guidance is in fair agreement that a strong low pressure system will move into the Southwest US ahead of a massive high pressure system in the northeast Pacific, just off the West Coast of the US. This storm system will drop further south into northern Baja California in the days after this forecast image, which is valid for the evening of February 8th. The different shades of colors show confidence levels of the NCEP Ensembles as shown on the blue numbers on the legend at the bottom of the image. You can see that the center of this low pressure system has deep oranges, which correlates to 54% probability of the system ending up there- a fair chance this far out. Notice that there is a very zonal pattern across the central and east US. These zonal wind flows (zonal means west-to-east wind flow) typically result in relatively dry and warm weather across much of the nation. I can already see that this type of pattern could result in a very similar set-up as we enter this storm potential period. If you look back towards the West Coast, you will see that storm system pressing down on the pressure contours, as well as another area in the Pacific pushing up on the pressure contours. These are opposing low and high pressure centers, respectively. If we see the low pressure system drop further south and that high pressure system try to bleed east into the Pacific Northwest, it is very plausible we could see the infamous Rex Block formation emerge.

As illustrated in the above image (made by, the Rex Block involves high pressure and low pressure essentially sitting on top of each other. This can happen anywhere, but for all intents and purposes, it has been shown on the West Coast. If you look downstream towards the central and east US, we again see that zonal flow pattern emerging in the East as a result of this Rex Block.

This is the latest European model forecast for the 11th of February. We can see our winter storm is actually in the Plains and shown as the tight gradient of pressure contours just south of the green-ish color in the region. This comes as a result of not the Rex Block (which is present in this image), but an amazingly-strong high pressure system in the Southeast. While many areas would see rain changing to snow in this event, should this storm even happen, the Southeast Ridge could really get in the way.

To be honest, I don't see this Southeast ridge happening. The only way we could see it would be in an extreme negative Pacific-North American index phase. When that index is negative, low pressure dominates the West Coast, and high pressure forms in the Southeast as a result. However, a glance at this and the previous run of the European model shows actually a positive PNA, which supports storm systems hitting the Midwest and Ohio Valley, rather than the Northern Plains. So I do not support the European model at the moment.

The American GFS model has been showing a pretty consistent solution of having a storm system moving out of the Front Range before sliding northeast and impacting the Upper Midwest, portions of the Central and Northern Plains as well as the Great Lakes. While this is nowhere near as extreme as the European model, this American model still does have a Southeast Ridge, although it is weaker than the European's. This is indeed a much more plausible solution in my opinion, with no unreasonably-strong ridge of high pressure in the East, when the atmospheric pattern does not support it.

I will continue updating this situation as the date draws closer.



Steve Mims said...

So Andrew, as I read your well-written synopsis, you are suggesting that the mid-Atlantic will not "enjoy" snow IF the storm develops?

Anonymous said...

Hey..where did your Spring forecast go? Bring that back!

Anonymous said...

spring is coming
but so are higher food prices if the heartland does not get any snow or rain i am sure nobody wants to pay $5 for a loaf of plain bread or $10 for a pound of hambuger but if we dont get any breaks form the drought food prices WILL go up count on it
winter is slippin away but i hope it goes out with a monster snow

Eric said...

The ECMWF issues with location of this potential storm system and the Southeast Ridge, although the PNA is relatively neutral can be easily explained by its bias to be too slow with storm systems over the southwestern US, thus it is allowing for stronger heights to pump to the east of this potential storm and deflect it northward.