Layer thickness, or the depth through a layer, is used by the forecaster to determine the type of precipitation expected, as well as several other forecast evaluations. The thickness of a layer is a function of the temperature and the moisture content. The warmer the air through a layer, the thicker the layer. The thickness scales are printed

on the Skew T for the standard lavers routinely . evaluated. To compute layer thickness on plotted Skew T, follow these steps:

1. Determine if the dew point curve through the layer indicates an average moisture greater than 3 g/kg.  

a. If the average moisture is greater than 3 g/kg, the virtual temperature curve should be constructed for the layer.

b. If the average moisture is less than 3 g/kg, the difference between the virtual temperature curve and the actual temperature curve will be very slight, and the actual temperature curve may be used in place of a virtual temperature curve.

2. Bisect the virtual temperature curve (or actual temperature curve) through the layer with a vertical line so the area enclosed by your vertical line, the upper and lower isobars, and the temperature curve is approximately equal. See figure 6-2-3.

3. Read the layer thickness where your vertical line intersects the appropriate thickness scale.

Freezing level is the height, or heights, in the atmosphere where the temperature falls below the freezing point of water. Finding it is a fairly straightforward process. Follow the plotted temperature curve up until you intersect the 0C isotherm. If your temperature curve is progressing from warmer to colder temperatures, you have a freezing level. Determine the height of this pressure level using the pressure-altitude curve. There may be more than one freezing level above a station at any one time.

Learning Objective: Describe the computa-tion procedure used to find the forecast surface temperatures on the Skew T.

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