Saturday, April 11, 2015

Another Moisture Starved System?

Nice view of Baboquivari Peak a bit after 7:00 am MST this morning, looking south from Kitt Peak.

The models are now very much in agreement this morning that tomorrow's weather event will just brush the southeast corner of Arizona and focus mostly in the Mexican mountains south of the border. Forecast of 500 mb winds and temperature (below from 06Z WRF-NAM forecast on 5.4 km grid) is valid at noon tomorrow (Sunday, April 12th) and shows the 500 mb cyclone centered over the border south of Tucson. Temperatures appear to be forecast in the -15 to -18 C range, with coldest 500 mb temperatures considerably to the south and east, over Mexico.

The WRF-NAM forecast of the TWC skewT valid at 6:00 pm tomorrow afternoon (above from 2.8 km grid) indicates cloud bases above 700 mb, a distressingly dry layer below that, and no CAPE. The forecast of PW valid at same time (below), shows the moisture-starved character of this event as currently forecast. Maximum PW over eastern Pima County struggles to reach 18 mm (7/10s of an inch). These forecasts from the WRF-NAM indicate an unsettled day over the greater Tucson area tomorrow, with: heavy cloud cover, mammatus, virga, sprinkles, and localized gusty winds. 

Finally, the WRF-NAM forecasts of total precipitation through midnight Sunday night are shown above for 5.4 km grid, and below for 2.8 km grid. The GFS version of the WRF is a bit drier, as is the latest NWS NAM forecast this morning. Regardless, best chance for light, but measurable, rainfall will be over the higher elevations of eastern Pima County.

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