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Friday's Winter Weather

Looking out to Friday, a large swath of Indiana may be impacted by precipitation. The first figure shows the 3 hour total precipitation for 2100 UTC on the 31st of October (Friday). The second figure shows the 700 mb map of omega and RH with heights. Although the largest (negative) values of omega are seen to the east of Indiana, there is still relatively strong (negative) values for omega over Indiana. The forcing behind this lift can be explained, in part, by the third and fourth figures. The third figure is of the QG temperature forcing. It shows negative values over Indiana which would indicate sinking motion, however, the QG absolute vorticity advection (Geo) term in the fourth figure shows a VORT max entering the western border of Indiana allowing for a large swatch of Indiana to be under positive vorticity advection. This term is the forcing that allows for the rising motion to produce precipitation.

The last figure is of a sounding showing a vertical modeled snapshot of the atmosphere over Lafayette at 1800 UTC. There is a saturated layer aloft that is completely below the freezing temperature with the top of this layer being at -20 degree Celsius. If snow develops, this sounding shows a relatively small melting layer near the surface along with a surface temperature above freezing. However, the surface at this time is 2-3 degrees above freezing. With dentritic growth possible (if snow is developing), a transition from freezing rain to snow by the early afternoon hours. With a warmer surface, this may not have a significant impact on road travel, since at this time, we may see an atmosphere that is quickly drying out and a surface that may melt any precip in the form of snow.