Saturday, February 1, 2014

Rain & Snow Potential

**Winter Storm Watch from 3 pm Sunday to 9 am Monday.**

As mentioned in the last forecast discussion, wintry weather was possible from Sunday morning into Sunday night. It was also mentioned that the forecast for Sunday was a low confidence forecast. This was because of the large variability/uncertainly in the forecast computer models used to analyze the weather. Models have now come into good agreement on the chance of snow Sunday evening/overnight... the question remains how much and what time.

Currently there is a low pressure centered near the eastern Great Lakes with a cold front extending southward through the Ohio Valley. Scattered showers extend generally along the front back into Arkansas. This front and the associated showers are generally headed in our direction and thus scattered rain showers are expected overnight. Scattered showers should be moving into our area generally around midnight this tonight and will continue off-and-on into Sunday morning.

Tomorrow is when things get interesting because colder air will filter in overnight behind the aforementioned cold front. By tomorrow morning temperatures will have fallen around 40 and possibly as low as the upper 30s.

Temperatures will hold steady for the most part through noon as areas of scattered light showers or areas of drizzle continue. By around the noon time showers will once again be increasing in coverage as a result of a wave of low pressure which will ride northeastward along the slow moving cold front. By afternoon, steady rain showers will once again be spread across south-central Kentucky. All told, rainfall should be in the 0.40 to 0.80" range before a transition to snow will occur. Some locations could see up to an inch of rain.

NAM model valid for 9pm tomorrow. The blue line on this model is a rough estimation of where the rain/snow line will be. Notice that it cuts right through south-central Kentucky which is an indication of just how tricky this forecast is.
The time of transition from rain to snow is very tricky. Furthermore there could be a time of some sleet mixing in with rain and then snow and if temperatures cool quick enough at the surface, even a brief round of light freezing rain is possible. The best educated "guess" at a change over time is between 6 pm and 10 pm. I realize a 4 hour window is very large but even at this point, it is just to difficult to say. The dividing line will be very close to our area and if the temperatures in the atmosphere can cool off just enough early on, a transition to snow will occur earlier. If it can't though, it may be that areas just to our north are seeing snow while our area hangs on to rain for several more hours. Truly just a tough call.

Obviously, the time of changeover will affect the amount of total snowfall. If a transition to snow occurs earlier... in general more snow; if later... in general less snow. There also remain questions about just how much moisture will be fed into the area after the transition occurs. For now, I expect accumulations to be in general 1-3 inches though I wouldn't be surprised if some locations saw locally around 4". After snowfall begins to fall, temperatures will drop below freezing.

Regardless of the exact amount and even timing of the snow, the confidence of at least some snow with deteriorating driving conditions is high. Thus it is recommended not to travel during the late afternoon and especially the evening hours Sunday. Temperatures will drop into the upper 20s overnight Sunday.

Snow showers will end before daybreak. However, at least a few areas of flurries will remain possible through Monday morning.

Note that this forecasts has a lot of uncertainties at this time and some adjustments with the forecast are likely. Accumulating snowfall seems likely but the transition time and the total accumulation remain question marks. Brain Urbancic will provide an update with the latest thoughts tomorrow. Please check back for the updated information.

Forecaster: Ryan Difani

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