Monday, August 07, 2006

Three very different morning soundings

There has been a substantial increase in low-level moisture during the night over southeastern and south-central Arizona. This moistening was related to outflows from both local convection and a large MCS in northern Sonora, in combination with some larger-scale advection as a strong 500 mb cyclone pulls north into the western US.

The overnight increase of precipitable water at Hermosilla, MX, was quite spectacular - as per Pat Holbrook's comments last evening. The following is a link to the GPS precipitable water time series at U of A atmospheric science.

Thunderstorms moved into central and south Tucson last evening with thunder and light rain observed at Davis Monthan AFB and light rain (but no thunder or lightning) observed at NWS TUS. Lightning was clearly visible from our house but apparently no showers up here in the north metro.

The morning soundings at Tucson, Phoenix, and Yuma are quite different from each other.

CLICK HERE to see the 12z soundings for these 3 locations.

Both Phoenix and Tucson, with heating, have the most potential CAPE observed since the 25th of July. The winds are very light at Tucson above 800 mb, indicating a good potential for heavy rainstorms and possible hail over higher elevations. In contrast, Phoenix has a strongly veering wind profile that would favor strong storms and possible severe wind gusts - however, the Phoenix wind profile should trend toward that of Tucson. Phoenix may also be vulnerable to low-level drying, since drier air is very close to the west. Definitely a difficult forecast situation at Phoenix!

In contrast, Yuma has strong veering winds but remains very dry and stable. I still expect a dramatic low-level moisture increase at Yuma, as the air sample by GPS at Hermosilla moves northward into Arizona.

It will be interesting to see how things evolve today.

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