Wednesday, January 11, 2017

Another Round of Wintry Weather Tonight

It will be another rough commute this evening for some, with more wintry weather possible late this afternoon.

A Winter Weather Advisory will go into effect at 1pm for Green county in southern Wisconsin, and 5pm for Rock and Walworth counties. A Freezing Rain Advisory will go into effect for western Illinois at 3pm, and 5pm for most of northern Illinois. Ice accumulations will be near a tenth of an inch, but will cause slick travel this evening. 

After a brief break in wintry weather this morning, we keep the potential for icy weather to return this evening. Light showers will move in this afternoon with temperatures still in the upper 30's. A cold front currently positioned through northern Iowa and northern Wisconsin will sink south through the afternoon. This will slowly push cold air southward as well, and temperatures will fall late this afternoon. This will bring the potential for freezing rain or drizzle in the evening and overnight tonight, along with affecting portions of the commute home. It all depends on how quickly and far south the front travels today

The best timeline for rain will be around 1pm today and will continue through about 6pm, at this time cold air will be moving in and dropping temperatures at the surface which brings then a chance for freezing rain and drizzle. Western areas of the Stateline can expect the slick weather as early as about 3pm and then areas east closer to 5/6pm.

As the front sinks, cold air will under cut warmer air aloft, which creates a mixed bag of  winter weather. The depth of warm air aloft determines the type of precipitation we see at the surface. If the warm air depth goes the whole way from top to bottom, then precipitation will fall as rain. Its the warm air layer is deep, but there is shallow sub-freezing air at the surface, this creates freezing rain as ice pellets melt moving through the warm layer, but then freeze on surface contact. Sleet is created when there is enough warm air aloft to melt any snow or ice as it falls, but there is still enough cold air below for it to freeze again before it hits the surface. As snow lacks a warm air layer, and there isn't much melting.

As for the forecast, while ice accumulations won't be high, the weather this evening will still cause slick areas on untreated roads through tomorrow morning and potentially hazardous driving conditions. Take it slow if you have to head out this evening

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