Monday, February 13, 2012

The European Cold Snap

It has been an amazing stretch of wintry weather across much of Europe and Central Asia, with feet of snow falling across portions of Italy, Romania, the Balkan states while temperatures in Prague have been some 15 to 25 degrees below average on a daily basis for the past two weeks.   Moscow hasn't been above 15 degrees for a daily high temperature since January 20th when they topped out at 17.  Snow...and even thundersnow...fell in Rome late last week. The images of snow on the left and below are from the Abruzzo region of Italy (generally the middle of the country near the Apennine range of mountains that run down the middle of the Italian peninsula), a hilly region where it does snow...just not as much as they've received in recent days and weeks...where they're measuring snowfall by the meter.

Needless to say...the unusual winter of 2012 has been fickle in the lower 48, but much more potent elsewhere.

The atmosphere in our part of the world hasn't been favorable for pronounced cold but it has been for Europe.  The arctic oscillation shifted negative late in January and has been generally negative for the better part of the last two weeks.  While that normally yields a colder pattern in the East, an unfavorable Pacific pattern is overruling the ability for the East to sustain colder temperatures.  We're cooler than we were when January ended and February began, but since the uber cold never could get itself going on our side of the hemisphere our part of the world never could quite tank in the temperature department like Europe could.  The cold dome over Europe now had its origins in Central Asia in mid to late January.  The cold dome retrograded westward towards Eastern Europe as the arctic blocking pattern set up.  Strong ridging of high pressure also set up shop over Russia, which set up the arctic block and then allowed the cold to slip into Europe from the East...a modern day "cold" war if you will.

Despite a favorable setup with arctic blocking. the East Coast was never really able to cash in as the pattern is transient thanks to a zonal pattern in the Pacific for the beginning portions of February.  Despite the brief intrusion of cold in the eastern half of the country the past couple of days, the lack of cooperation from the Pacific by blasting a stronger jet into the west coast is preventing a more "locked and blocked" look on this side of the world.  In the past couple of winters, when we had arctic blocking the Pacific was typically in a less 'zonal' state and had a decent ridge aloft in the Eastern Pacific, which set up our cold and snowy look.   Past winters like 1999 and 1956 had similar setups where Europe was cold and we were not despite strong blocking in the Arctic.  In fact, the temperature profile for Europe in the first nine days of February between this year  (first graphic below) and 1956 (second graphic) are remarkably similar.

Philadelphia's temperatures during the first couple of weeks of February 1956 were rather unimpressive -- highs in the 40's and 50's, lows around 30.  One wintry event on the 4th brought a tiny bit of snow on the front end of the storm but otherwise it was a bit rainy, a bit mild here...while Europe shivered.