Pattern Change: Here comes winter
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Latest NOAA 30-day outlook for December favors colder than average temperatures over much of the USA.
It appears our on again, off again seasons are about to turn on again. In a big way.
The latest series of medium range forecast models are screaming winter for the Midwest. The so called "polar front" jet stream is about to buckle, and send wave after wave of frigid air into the nation's midsection. At this time it appears the pattern may last right into mid-December.
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NOAA GFS model 500 millibar (18,000 feet) chart shows deep trough over the central U.S. Friday. This upper air pattern can drive cold air all the way down to the Gulf of Mexico.
The colder than average pattern would be a departure for moderate strength El Nino events in Minnesota. There is about a 71% correlation between milder than average winters in Minnesota during moderate strength (Tropical Pacific SST's +1.2 to +1.8 degrees) El Nino years.
In a recent look at moderate strength El Nino years since 1950, the Twin Cities NWS found that every December has been milder than average in those events. If it happens, this would be the first cooler than average December in a moderate El Nino year.
The cold blast this week should be enough to begin to freeze up open water in ponds and small bays this week in area lakes. Safe skating and ice fishing is likely at least two or three weeks away though. The average date of initial soil freeze in the Twin Cities is December 8th. The coming cold wave and lack of insulating snow cover may put us right on schedule this year.
Hopefully your outdoor holiday light display is all done by now!
PH