Wednesday, December 15, 2010

Thoughts on the current winter weather situation

A Winter Weather Advisory is now in effect until noon for the metro counties (3pm for Tipton Co. and points north) as light precipitation has developed and is moving east through the area. I expect light precip to continue to develop through the morning hours and affect the region as a warm front to our south starts moving in our direction.

Temperatures and dewpoints are crucial at this time, with the majority of the suburban area remaining just above freezing (35 at Memphis Int'l seems to be the warmest spot) and dewpoints still in the teens. I believe that as precipitation continues, temperatures will drop slightly and dewpoints will rise - caused by a process called evaporative cooling, in which moisture falling through a column of dry air moistens that column and cools the surrounding air.

A small amount of evaporative cooling will bring temps to near or just below freezing for a few hours this morning before rising again (back above freezing) by mid-morning. The biggest question is whether enough precipitation will affect the region to cause those temps to fall to freezing. For now, I believe that we will continue to see additional precipitation forming and, assuming this occurs, expect temps to dip slightly before rebounding later in the morning. Thus, a chance of freezing rain and/or sleet through mid-morning throughout the metro.

With temperatures already so close to freezing, please be extremely cautious on your commute into work or school this morning. A degree here or there could mean the difference between a glaze of ice (which is hard to see on roadways) and just wet streets., this blog, and MWN on Facebook and Twitter will be updated throughout the morning. Stay tuned...

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