Using the Metar at an appropriate airport, first get the temperature. In this example, KOSC. Oscoda, Michigan.
KOSC 090216Z AUTO 31010KT 10SM -SN SCT039 OVC050 M08/M11 A2985
The temperature is -8C.
Then go to the ADDS.GOV website, and the satellite page, select the infrared images. http://aviationweather.gov/adds/satellite/displaySat.php?region=DTW&isingle=single&itype=ir
This is showing the temperature
(in C) of the cloud TOPS.
Note the green cloud tops over OSC and the temperature across the top that matches it, somewhere around -22.
Find the difference in temperatures from the surface to the cloud tops.
The difference between -8 and -22 = -16 or 16 degrees.
The normal lapse rate is 2 degrees C for every 1000 feet, so then we divide 16 by 2 and get 8 (thousand feet). 8000 feet above the surface is the top of the clouds.
Going back to the METAR,
KOSC 090216Z AUTO 31010KT 10SM -SN SCT039 OVC050 M08/M11 A2985
We see that the bases of the overcast are around 5000 feet, so we would have to fly through approximately 3000 feet of clouds, to get to the tops.
Right now, there are no PIREPS to confirm our little test, but you can practice it while you are sitting around wishing you were flying this weekend.
Here is an interesting document:
Using the Velocity Azimuth Display (VAD), you can get the estimated cloud TOPS. The NOAA people pointed us to this technique.
http://www.skymachines.com/mountain-flying/Little-Known-Pilot-Weather-Tools.PDF
EDITOR’S NOTE: Thanks to Bob “Riff” Riffel, Mich. Bureau of Aeronautics (Ret.), for sharing this with us.
