Thursday, July 02, 2015

Fireworks On Hold Currently

Strongest thunderstorm activity shifted to northeast Arizona yesterday evening. The IR image above from 03 UTC shows a large storm complex over the Navajo Nation, where there were reports of severe hail. Unusual to see such a large complex up in that part of state, but the WRF seemed to predict it fairly well yesterday.

Locally, we saw a return to more typical summer frustrations, as storms on the mountains and to south produced heavy anvil cloud that shut down all storm development over lower elevations. The CG flash plot through midnight last night (above) shows very much reduced thunderstorm activity across all of southeastern Arizona.

This morning the 500 mb anticyclone over the West has two distinct circulation centers - one over northwestern Nevada and the other near the Four Corners. Flow and subsidence around the southeast portion of the Four Corners anticyclone center is bringing warm and drier middle-level air across much of New Mexico and Arizona. The 13 UTC water vapor image below shows that upper-tropospheric dryness is spreading over Arizona from the southeast.

The TWC 12 UTC morning sounding (above) remained moist with PW at 40 mm (which was a bit higher than the concurrent GPS estimate). The 06 UTC WRF-NAM forecast sounding for TWC at 12 UTC was too dry, with PW at 34 mm. By 5:00 pm MST this afternoon the WRF-NAM forecast sounding (below) has dried out (PW down to 28 mm) and stabilized tremendously. In response, the WRF variants forecast virtually no thunderstorm activity today across most of southern Arizona. One question will be whether or not the large-scale drying and subsidence can completely shut down convective development over the highest mountains, where small-scale, orographic-forced vertical motions will be stronger than the large-scale fields. I would suspect that there may be some isolated, mountain storms this afternoon.

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