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This sounding taken in Fort Worth, Texas is from December 4th, 1996. This and the other soundings in this module were produced from a former sounding page at the University of Illinois. Real-time soundings are available, for example, at UCAR Weather under "Skew-T/Log-P diagrams" and a good site for historical soundings can be found at the University of Wyoming. The colors of the lines change depending on which program (or programmer) produces the diagram. But you can always tell the background lines apart by their slope, as I discussed on the previous page.
The foreground lines, in this case, are black. The line on the right (always) is the temperature, and the line on the left is the dew point. For example, at 700 mb, the temperature is 0 C and the dew point is about -6 C. Notice how temperature is much colder at higher elevations (lower pressures): at 200 mb the temperature is -59 C, rather bone-chilling. And yet commercial aircraft still require air conditioning, for reasons you will learn in your thermodynamics course.
Take a closer look now at the temperature structure. The lowest data, at the ground, is at 1000 mb. There, the temperature is about 3 C. But the temperature increases rapidly with height, rising to 9 C at 980 mb and over 10 C at 940 mb. This is called a temperature inversion. These are common at night, when the ground cools off and cools the air above it. This sounding was taken at 12Z, or 6 AM local time.
Another layer where the temperature is nearly constant with height occurs at the top of the sounding, above 180 mb. This is the lower portion of the stratosphere, and the boundary between the stratosphere and troposphere where the temperature line takes a sharp turn to the right is called the tropopause.
Finally, notice the layer between 400 mb and 430 mb where the temperature and dew point lines almost meet. If the temperature is almost as cold as the dew point, that means that the air is nearly saturated. From experience, layers in which the temperature and dew point are within about three degrees of each other, according to a rawinsonde observation, probably really are saturated and filled with cloud. If you had been reading this the same day as the sounding, you may have noticed a high overcast all day. From this sounding, we can see that the cloud deck has its base at 430 mb (an altitude of about 4 mi) and is about 30 mb thick.
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