Friday, October 22, 2010

Minneapolis at 16th Day Past Average First Freeze;
Eighth Longest Dry Spell at 27 Days

Minnesota winters start early, but the low temperature of 36° this morning at Minneapolis marked the 16th day since the date of the average first freezing temperature. The Minnesota Public Radio Updraft blog noted yesterday that the average date of first 32° temperature in the fall is October 6. The latest forecast calls for temperatures to decline next week, but the non-freezing streak could complete a third week with the low not expected to reach 32° until Thursday, the 28th. This would be a tie for the 10th latest first freeze; the most recent occurrence was in 2007.

Updraft notes that the trace of precipitation so far makes this the driest October on record, although the National Weather Service reports that is likely to change by tomorrow with a 60% chance of rain. The 27-day stretch without measurable precipitation since Sept. 26 is now the 8th longest dry spell in Minneapolis history. The longest was 51 days from Nov. 15, 1943 to Jan 4, 1944. Minneapolis records began in 1871. It's also the 8th longest dry spell on record at St. Cloud, where records date back to 1940.

The unusually warm and dry conditions are the result of the jet stream remaining north of the region. The chart shows that the average jet stream for the past month has been mainly located over southern Canada.

Images (click to enlarge): Minnesota precipitation departure from average, Sept. 26, 2010 to Oct. 21, 2010, from National Weather Service; Average jet stream (250 mb wind), Sept. 19, 2010 to Oct. 20, 2010, from Earth System Research Laboratory/Physical Sciences Division/NOAA

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