Sunday, July 04, 2010

Diurnal Td Surges at Yuma

An earlier post showed that WRF was forecasting a push of low-level moisture up the Gulf of California for yesterday morning. That did indeed happen - Td at Yuma yesterday morning at 6 am was 23F and at 8 am it was 69F. However, the low-level moisture quickly mixed out after a couple of hours. This morning at 6 am Yuma's dewpoint was again 69F, with strong southerly winds - see top image which is VAD wind profile from the NWS radar at Yuma. The low-level, southerly winds reach up to 2,000 to 3,000 ft. The satellite PW product (lower image) indicates that PW values are higher up the Gulf and into the deserts of southwest and south central AZ. With very dry air aloft, the higher dewpoints will mix out dramatically during the day. This is a typical diurnal cycle that we often see this time of year - daily late night/early morning sloshes of high dewpoint air north from the Gulf. This process helps gradually raise low-level moisture, but is much different than the impulsive Gulf surges that can bring large, and much deeper changes, within the course of a few hours.

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