Monday, August 18, 2014

Brief Summary Of August 17th

First, the large Mexican MCS weakened shortly after the image shown in previous post. A new, but smaller MCS developed along the Borderlands and moved westward during the night and is now out in the lower Colorado River Basin.

Strong storms developed late yesterday afternoon, as shown above in composite radar image from about 6:30 pm MST. Photo below shows these storms looming over Tucson off to the east. The storms weakened as they moved into lower elevations. Here at the house we had thunder, more rainbows, a strong outflow of 30 to 40 mph, but only a sprinkle of rain after dark. Total remained at only 0.14" here at the house.

Plot of CG flashes (above for 24-hours ending at 6 am this morning) shows another day of widespread thunderstorms across southern Arizona. The bright colors indicate activity at sunrise along the Colorado and also on the Rim. MesoWest rainfall plots (24-hours ending at 7 am) show the widespread character of the rain - note the 2 inch plus amount east of the Rincons in the San Pedro Valley.

Across the ALERT network 65 stations reported rainfall for 24-hours ending at 7 am MST (a bit over 70% areal coverage and down a bit from Saturday). There 10 sites with half an inch or more and 4 of these had over an inch. The Rillito was flowing in about half the wash at sunrise but high water marks indicated that it had flowed bank-to-bank during the night. The USGS gauge at Dodge and Rillito (bottom below) indicated that flow reached almost 4,000 cfs a bit after midnight - quite a flow and the greatest in quite some time.

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