Monday, September 28, 2015

More Misuse of Water-Vapor Images

By: Lee Grenci , 12:31AM,GMT on September 29,2015






If I see one more forecaster present a water vapor image and point to the ribbon of bright colors and bright white extending northward from the eastern Gulf of Mexico / Florida and describe it as a "plume of tropical moisture," I'm going to scream. First, those are high cloud tops (composed of mostly ice crystals) and NOT water vapor. Yes, high cloud tops contaminate water vapor images! Second, even if it were water vapor (and it's NOT), the temperatures of these features in this "plume" are -50 degrees Celsius, -60 degrees Celsius and even minus 70 degrees Celsius (or lower). Do you know how much water vapor resides at these kinds of rarefied frigid altitudes? You guessed it! Not very much. It is just so disheartening to see forecasters use water vapor images to "infer" lower-tropospheric moisture content. It's just bad science, plain and simple.


An enhanced water-vapor image at 2315 UTC on September 28, 2015. Courtesy of UCAR.

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