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One last thing to worry about with regards to changing and moving air masses: elevation. Even if no heat is being added to or taken away from an air mass, it can still warm and cool just from changes in elevation. That's because changes in elevation correspond to changes in pressure. As air moves to higher pressure without the addition or subtraction of heat ("adiabatically"), both its density and temperature increase. The temperature change is a known constant: about 10 degrees Celsius per kilometer.
Let's go back to our Rapid City example and change it around a bit. Rapid City and Goodland are both about the same elevation. Suppose instead that the wind is from the southeast at 15 knots and that a temperature of 77 degrees is found upstream at Omaha, Nebraska (MAP). That 77 degree air from Omaha would make it to Rapid City the next day. But Rapid City is higher than Omaha: the air mass will cool a bit from the elevation change. How much?
Using the STATIONS command in Weather to find out the height (in meters) of the two stations:
CD STATION ICAO IATA SYNOP LAT LONG ELEV S T U F HNE OMAHA/EPPLEY KOMA OMA 72550 41 18N 095 54W 299 X X ASD RAPID CITY KRAP RAP 44 03N 103 04W 970 X X AOmaha is 700 m lower than Rapid City. Therefore, air will cool 7 C as it travels from Omaha to Rapid City, just from the change in elevation. Now let's do the math: 77 F is 25 C. Subtract 7 C, and you get 18 C. That's about 64 F. So when you factor in the elevation difference, you find that the temperature in Rapid City ought to remain in the mid 60s. The warmer air in Omaha will cool as it rises.
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