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Daryl Ritchison, WDAY, Published July 19 2013

Weather Talk: This time of year, area records net moisture loss

Evapotranspiration is the water evaporated from the ground back to the atmosphere both as transpiration from the leaves of plants and also as direct evaporation from open water and soil. The amount of water evaporated changes from day to day based on cloud cover, wind, relative humidity, temperature and other influences.

On a sunny day this time of year, approximately one-third of an inch of moisture is evaporated in a day. On a cloudy day, that amount may be a tenth of an inch or less. Although you may think a day with rain would have a net gain of moisture, if it was light and the sun was out for a period of time, an overall net loss is still possible.

As a general rule, this area will record a net loss of moisture until the second half of September. That is why, historically, the autumn rains were always beneficial to resupply the soils with moisture, although our frequent wet conditions during the past 20 years has changed that to some degree.

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