Sunday, September 23, 2012

Special Long Range Lookout: Sustained Cold In Long Range

This is a special edition of 'Long Range Lookout', being presented after the 12z GFS brings unseasonably cold air to much of the north and west parts of the nation.

As seen above, the 11-15 day average for 850mb temperature anomalies is very cold- as low as 14 degrees below normal. This actually puts the 850mb temperatures cold enough to produce snow- an occurrence being shown by the same 12z GFS.

As is to be expected, the long range verifies a very small part of the time, so one would usually take this with a grain of salt. However, looking at past trends of the last few runs of the GFS focused on 11-15 day 850mb temp anomalies, the model has been steadily trending colder with each run. What I would take away from this is that an enhanced appearance of cold weather is likely in the next couple of weeks, but the intensity is unknown.

Also of interest is the 11-15 day 500mb height anomalies. Notice the strong signs of a positive PNA, with a strong ridge in eastern Alaska and western Canada. However, the lack of a ridge near Greenland will result in an obstacle of being able to get the cold air east.

Considering there is a strong disturbance anomaly over south central Canada and central Canada, there should be at least one storm system that sweeps cold air east and into the Midwest and Mississippi Valley. The west-to-east motion of systems in the North Hemisphere means that this cold air will eventually move east into the eastern US, but the intensity of that cold air is in question.

Andrew

4 comments:

Joshua Steiner said...

Hey, Andrew.. I've always wanted to know. From what site do you get these maps? I think it would be great if I had more sites to get computer models from..

WinterStorm said...

Hi Joshua! I did some searching and found them:
Allan's Model and Weather Data Page: Click Here

Anonymous said...

Thanks Joshua, I came here to ask the same question!

Aran Jacobs said...

Thanks for the update.