| SOIL MOISTURE AND FORECASTING
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METEOROLOGIST JEFF HABY
Soil moisture is important to forecasting. When the soil is saturated, evaporation from the earth's surface and
transpiration from trees will modify the weather. During the day, the evaporation and transpiration cause the air
to be cooler than it otherwise would have been BUT
also adds moisture to the air. In
warm climates, the added
moisture can more than offset the cooling from evaporation when it comes to how comfortable the air feels. A
temperature of 95 with a dewpoint of 75 feels much
more uncomfortable than a temperature of 100 with a dewpoint of 50.
Saturated soils increase the likelihood for
dew and
frost, especially on clear
nights with light wind. The soil moisture increases the dewpoint, which in
turn causes the air above the surface to be closer to saturation. Soil moisture is also important to
instability.
The addition of moisture from evaporation and transpiration add moisture to the air which can increase the
likelihood of rain when a front or another trigger mechanism moves through. An extended period of
dry weather will cause soil moisture values to be below normal.
This has an effect of reducing rainfall (less evapotranspiration results in less moisture for
fronts to lift and less thermodynamic instability). Saturated soils can also give you a muddy shoe (be careful
where you walk).
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