Thursday, December 2, 2010

Midday Update: 4-8" Still Expected Friday PM Hours (Storm Watch)

* No travel problems today, tonight or first thing Friday morning. I don't expect any snowy headaches for the AM commute Friday, but getting home later tomorrow will be slow and very icy. The reason? It's much harder keeping major highways wet/slushy with an air temperature in the upper teens to 20 - even the freeways and interstates may become snow-covered, especially after 4 or 5 pm Friday.

* 12Z NAM/WRF model data prints out .44" for MSP Friday PM hours. That's a little less than last night's run, which printed out .56". With a snow/rain ratio close to 20/1 that could still translate into 4-8" for the western and southern suburbs, maybe 3-4" for the northern/eastern suburbs. I still feel (reasonably) comfortable saying 4-8" of light, fluffy, powdery snow during the PM hours tomorrow as an overall range for the metro area.

Winter Storm Watch. The local NWS office has issued a watch for most of central/southern MN - the metro area on the northern fringe of the watch area. A watch means 6"+ amounts possible during a 24 hour period. No mix of rain/ice with this storm - the atmosphere will be cold enough for all snow this time.
* Temperatures will be close to 20, which doesn't bode well for conditions on area highways. The chemicals MnDOT puts down work much faster when the mercury is close to 30-32 F. But at 20 F. these chemicals don't work nearly as quickly or effectively. Even the freeways may be snow-covered and icy by Friday evening. Plan on leaving 3 to 5 times more time to get around late in the day tomorrow.

How Much? The 12Z run backs off on the snow amounts (slightly). No more band of 8-10" showing up, clipper maxes out at 6-7" running through western/southern suburbs of MSP. Here is the latest NAM/WRF guidance - hinting at some 6" amounts of light, powdery snow across much of the metro, closer to 6-8" for the far western suburbs, toward St. Cloud, Willmar and Alexandria. A slight shift in the storm track could make the difference between 2" and 8" - but this still looks like a "plowable" snow event.

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