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SWRP Sounding
supercooled warm-rain process
Below is a sounding that typically results in freezing rain through
Supercooled Warm Rain Processes (SWRP).
Throughout the sounding profile,
the temperature never exceeds 0C (32F). The process begins as supercooled
raindrops grow by collision and coalescence, and since the temperature
throughout the cloud is
warmer than about -10C, the cloud is
generally free of ice crystals. This is important
because if ice crystals were present, the cloud drops would instead grow by
ice crystal processes, producing snow
and not freezing rain. Winds are typically out of the
west or northwest at the surface, veering to the southwest in
middle and upper levels.
In the second sounding, the temperature exceeds 0C (32F) above the cloud.
This type of sounding is commonly observed
in the Southern Plains where very
warm mid-level air from the Mexican plateau overrides colder air in the
surface layers. Winds at the surface are usually from the east or southeast
and veer around to the southwest or west in middle and upper levels.
The best way to forecast freezing rain is to examine forecast model
soundings for profiles similar to the ones described in this module.
One web site providing these products is the Northern Illinois University's
Storm Machine.
One can choose the city and model and receive the appropriate forecast
soundings, from which a forecast can be made about
when and where freezing rain will occur.
classic sounding
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Precipitation
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