Wednesday, July 29, 2015

Quick Look At Today - Wednesday, 29 July

Light showers continue this morning (composite radar above is for 7:15 am MST), with most echoes to the west and south of Tucson, moving toward the northwest. Heavy clouds cover much of Arizona, New Mexico, and northern Mexico this morning (visible satellite image below is from 7:00 am), meaning much reduced heating today is likely today.

The morning skewT plot of the TWC upper-air data (below, for 12 UTC from SPC) presents another onion shaped sounding, with cool, worked-over air below 800 or so mb. Winds aloft have increased from the south-southeast above 700 mb, providing a bit more steering flow for today. The directional shear profile remains fairly poor, but anvil shading may not be very important today, given stable low-levels and significant clouds. Typically, this would be a totally down day, however, the situation is a bit more complicated today. While the low-levels have been stabilized, a couple of layers aloft from 800 to 600 mb have considerable CAPE, if lifted a bit, thus elevated showers and thunderstorms are possible, if this situation continues through the day.

The forecast models are all over the place for today and I'll just discuss them very briefly. The 06 UTC runs of the WRF model at Atmo are quite different for this afternoon. The NAM version has mostly light showers, with  some thunderstorms on the mountains. The GFS version forecasts afternoon thunderstorms across the metro area. The new NWS NAM forecasts a very wet day for most all of southern Arizona, and keeps the weak, inverted trough at 500 mb nearly stationary out to our west. The 12 UTC run of the NWS HRRR forecasts rather anemic storm activity mostly to east and north of the Tucson area. It's best to wait for Mike's discussion of the latest morning runs of the WRF model

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