KATC StormTeam 3 Weather BLOG

Tonight will be another chilly one with optimal conditions anticipated for radiational cooling.  With dry high pressure in place and light winds, radiational cooling occurs when it is easy for the heat trapped near the surface and in the lowest layers of the atmosphere to escape aloft.  Warm air rises and in its wake we see a net cooling at the surface.  And that’s why we sometimes see frost when air temperatures are in the mid-upper 30s, even in the lower 40s.  Radiational cooling also occurs at the “micro” level which is generally lower than the 6 foot level that we actually measure temperature.  So when you see frost on grass it’s 32 deg or colder at grass level, while it can be a lot milder just a few feet up.  In addition, when you get down to ground level you also get an evaporative cooling factor from moisture in the ground, thereby giving us many opportunities for frost even when it’s not really that cold.  Normally our frostiest of nights in Acadiana are the second or third night after a cold air mass moves in.  So expect frosty conditions by morning with a subtle warm-up staying in the forecast for the rest of the week and into the weekend.  Showers still appear to be on tap for early next week.  Program Note:  Wednesday night I will be talking about our winter outlook for the area…can we expect a better chance of snow this winter?  Tune in and see!