Thursday, February 16, 2012

Will winter every fully arrive?

Last weekend's massive high pressure system brought some cooler air to the middle of the country, getting us slightly closer to more winter-like weather.  Compare the temperature anomalies from the first week of February nationally (from NCDC)... the temperature anomalies from the second week of February.
This shows a significant change in temperatures across the central part of the country--from well above normal (over 15 degrees Fahrenheit above normal for much of the northern plains) to near normal or slightly below normal for much of the high plains by the next week.  That dome of cold, high-pressure air really had an impact.

Cooler weather allowed snow to fall across the central and southern plains, generating one of Oklahoma's few snowstorms even in a relatively warm year.  Here was the snow depth map as of the morning of the 14th (from NOHRSC):
A good 1-2" across much of Oklahoma, with higher amounts to the north in Nebraska.  Of course, now two days later the snow has almost completely melted.  Here is this morning's snow analysis:

Much of the snow is gone--even back up into the Chicago area. Warmer weather looks to be returning...

The longer-term forecasts also seem to be pointing toward keeping the warm weather around for much of the eastern US at least through this week.  Compare the following three GFS forecast maps.  One for 500mb at 12Z tomorrow:
Notice a trough over eastern Canada, but there is no well-defined jet stream or any particularly outstanding jet streaks.  A small cut-off low in far southern Arizona and New Mexico may lead to severe weather in south Texas later on Friday.  Here's the 500mb forecast map for Saturday morning:

Still not a very well-defined jet stream, and even the trough and ridge pattern is not well defined.  This is not the signature of any strong push of cold air coming out of Canada any time soon.  Finally for Monday morning:
Still nothing impressive.  There looks to be large-scale troughing over much of the western US, but there are no organized jet streaks around the trough.  This implies that the temperature contrasts in the atmosphere beneath are pretty weak--very little in the way of strong organized fronts, probably.  Without strong pushes of cold air from the north, temperature in the pre-existing air mass should have time to moderate and warm a little.  I'm expecting the temperatures to remain at or slightly above normal for much of the eastern US for the next few days.  Winter is still on hold...

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