Sunday, March 4, 2012

Severe Weather Possible in the Long Range

Yesterday, I mentioned how the ridge currently in the Gulf of Alaska will be shifted south and a new low pressure system regime will take over.

Now, looking at the individual 12z GFS Ensembles, it looks like a good portion of the East US may be under the gun at some point in the next few weeks.

Here's one of the GFS Ensembles' 6-10 day 500mb height anomalies forecast. The ensemble member shows the Gulf of Alaska covered by a deep low pressure system. Also, there is a large ridge in the North US and a low pressure system in the south central US. I worry that the warm Gulf air moved both by the strong ridge will quickly interact with any low pressure system that may be present along the area delineated for a low pressure in the area.

The deep low in the Gulf of Alaska (GOA) will persistently spit out low pressure disturbances that will hit the US and come onshore to produce precipitation. As long as this vortex of low pressure is in the GOA, there will be a somewhat continuous threat of precipitation- from snow to severe weather.

Here I have delineated the area I think may be at risk with the low pressure systems that formulate in the Southern Plains. If they ride along the outskirts of the ridge, the Midwest may very well get in on the action. It comes down to this- as long as the Gulf of Mexico (GOM) is 'open for business' with warm, moist air flowing on land, severe weather is possible.

Now, the tornado threat will depend on how strong a system is and the proximity to the jet stream that will be displaced north. The vortex in the GOA makes for a cause-effect relationship that produces a ridge of high pressure in much of the east half of the US. That ridge then pushes the jet stream north, possibly as far north as the Canada/US border. If the storm system is weak and far south, the jet stream may not latch onto it and lessen the tornado threat. If the storm system is stronger, the jet stream may catch it and increase wind speed and the tornado threat.



ERN Wx said...

Andrew, the consistency of the Euro is wonderful. Deep East coast trough (0z run), no trough (12z run). I know you get furious when that happens.

Anonymous said...

Sorry, I commented on the wrong post. So, again..
When will some of these storms start making it up to southern michigan? Most forecasts I have seen are predicting a big warmup about a week from now, with temperatures right up near 60 degrees. Hopefully severe weather comes along with the warmth?
After winter, I can't wait for the first tornado warning of the season.

Andrew said...

Eastern WX: Yeah, it's pretty disappointing, especially for such a good model.

Anonymous: With such a big warm up, Im guessing your area will get some storms when the cold front comes through.

ERN WX said...

Yes! The PNA is going positive! The AO may go negative. The only problem is not until torwards the end of the month. Sad. Maybe the 12z run was a bad run?!? The Euro had been showing the trough for several straight runs. I will look at the 0z ru from tonight before I make that decision. I think everyone will agree, models have been so consistent this year. I am joking! Terrible winter. You need COLD winters to prevent these massive tornado outbreaks. Well, the cold certainly helps.

ERN WX said...

Andrew, I think we have a problem.

mike paulocsak said...

Hello ERN WX.We certainly do.Some idiot is posting rude comments!!!!!!!!! They need to go to another site.Please don't trash this one.

Andrew said...

Eastern WX and Mike: Thank you for alerting me to the problem. It has been corrected.