Flora and Fauna News

Generous Monsoon Season Draws to Close
By Michael Plagens Sonoran Desert Sciences
Tucson, Az.-----This summer's monsoon season, which brought abundant precipitation to many areas of the Sonoran Desert has now ended with an abruptly drier flow of air from the west. Arizona together with most of the southwestern United States has been in an extended drought over much of the past decade. The monsoon in Arizona / Sonoran Desert is a moist humid wind from the south and southeast. Air with dew points as high as 20°C when super-heated by hot desert sunshine can boil up into towering thunderheads. These convection storms have their best chance of forming when mountains provide a bit of lift to the air flow. Storms may drift from their formation site or else remain stationary. If upper level winds are favorable a stalled thunderstorm can drop up to 50 mm or more of precipitation in a very short time. Flash flooding is the result. Once the wind shifts back to a westerly flow, usually by mid September, the rains and humidity stop abruptly. Occasionally an errant tropical storm off the Mexican west coast will push abundant moisture up into Arizona as late as October. Already this year former Hurricane John passed into Arizona as it was breaking up, bringing torrential downpours to many desert areas.	An isolated thunderstorm like this one could drop significant rain in one desert location while leaving nearby areas parched. Photo © Jim Blaugh. Sponsored Links:

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Flora and Fauna News appears several times
per month and provides current information about the birds, insects and plants
(natural history) living in the Arizona Sonoran Desert.
Copyright Michael J. Plagens, 2010
Send questions or comments to mjplagens@arizonensis.org