Calculations for the maximum temperature on the Skew T should be done using the early morning, or cool, sounding for the day. For continental United States locations, this is normally done with the 1200Z plotted on a Skew T. Of course, many of us are not stationed in CONUS, and we have to use the available sounding that comes closest to the coolest part of the day, during the period near sunrise. In order to calculate the maximum expected temperature for the day, you must first determine if the day will be cloudy, with little solar insolation received at the surface, or sunny, with a great deal of solar insolation received at the surface.

Analysis of the current clouds and expected cloud development on the Skew T should provide this information, or consult the forecaster. If the day is expected to be mostly sunny, follow a dry adiabat from your 850-millibar temperature to the surface pressure level and read the temperature at the intersection. For mountainous areas and high elevations, you should adjust the procedure to start at a pressure level about 5,000 feet above the surface. If the day is expected to be mostly cloudy (broken cloud cover to overcast), follow a saturation adiabat from the 850-millibar level (or 5,000-foot AGL pressure level) to the surface pressure level and read the temperature at the intersection. See figure 6-2-4 for examples of the maximum temperature computations for sunny and cloudy conditions.

In summer air mass situations, strong radia-tion inversions routinely develop. If your plotted morning Skew T shows a radiation inversion with a top between 4,000 and 6,000 feet, you should use the temperature at the top of the inversion (the warmest point in the inversion) as the starting point in the computation, instead of the 850-miIlibar temperature.

Minimum temperature computations on the Skew T are not as reliable as maximum temperature computations on the Skew T. Many locations have developed methods using the Skew T that work well at one location but are not even close for a different location. Use locally derived procedures for your station if available. Other-wise, two methods for calculating minimum temperatures work fairly well at many locations. You may use either or both methods to find at least a ballpark value for the expected minimum temperature.

The first method uses the early morning sounding to predict a minimum temperature for the following morning. Essentially, this is a 24-hour forecast. From the 850-millibar dew point

Figure 6-2-4.-Computation of maximum temperature; with no inversion 4,000 to 6,000 feet and (A) mostly cloudy skies (B) mostly clear skies; with an inversion between 4,000 to 6,000 feet and (C) mostly cloudy skies (D) mostly clear skies.

temperature, follow a saturation adiabat to the current surface pressure level and read the temperature. An example is shown in figure 6-2-5. The write-up on this procedure does not mention an adjustment for high elevations, but if you are stationed at a high elevation, you may wish to experiment by using the dew point temperature at 5,000 feet.

A second technique does not actually require the use of the Skew T, although an after-noon sounding conducted near or at the time of maximum heating may be used. In this technique, the dew point temperature at the time of maximum heating is used as the estimate for the minimum temperature the following morning. 

We have just briefly described two procedures that may be used on the Skew T to compute maximum and minimum temperatures. I must stress that these values are just one input for a proper and accurate temperature fore-cast, and should not be used without careful forecaster consideration of climatology, numerical forecasts, advection, and other important atmospheric modifiers, which you will study in AG1&C.

Learning Objective: Define the use of and describe the computation procedures for cloud formation parameter analysis on the Skew T, Log P Diagram.

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