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Re: Near-adiabatic saturated layers
Posted By: Lyle Alexander In Response To: Re: Near-adiabatic saturated layers (richard mamrosh)
Date: 15-December-06 1605Z
In Response To: Re: Near-adiabatic saturated layers (richard mamrosh)
Scott and Rich,
This adiabatic case in saturation is very interesting. I have not paid close attention to this in the past but do notice that when there are low clouds over my area on the backside of a low, temperatures usually drop rather rapidly ascending through the cloud layer, in many cases getting colder at the cloud tops than forecasted by the models. In some cases, this will result in some icing (typically 3-5 thousand feet MSL) where temperatures were not forecast to be below freezing. Above that cloud layer, there is typically a sharp inversion with temperatures climbing back above freezing.
The Daily Weather Map for 16 Nov (12Z) shows an occluded surface low over Louisville, KY. A cold front extends from southwest Virginia southward through Savannah, GA. The point of interest (DNN) is in far northern Georgia in some wrap around low clouds.
I checked aircraft data from 12 to 18Z in the general area of DNN. I found several pieces of data, most without moisture information, a few which might have shown a temperature curve in a cloud layer with a lapse rate greater than moist adiabat but I didn't have enough data to know the level of the clouds. There are four TAMDAR soundings in the region that I selected. Three had good moisture in the low altitude, two of those showed a lapse rate nearly adiabatic. The third one (TRI descent 1655Z) was not quite saturated below the inversion.
The two soundings of interest were a descent into MSL at 1639Z and an ascent from CHA at 1727Z. The one for MSL is saturated to the point that you can't see the blue line except near the surface and then starting near 700 mb but the text indicates that the dew point data was there.
I looked for icing from these aircraft but did not find any according to the sensors (even though portions of the layers were below freezing).
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