Thursday, August 07, 2014

Low-level Moisture Push Into Pima County Today?

First a look at the very active, tropical Pacific. Above is MIMIC PW, from CIMSS at University of Wisconsin valid at 11 UTC this morning, showing three tropical storms curled up across the Pacific. Out at 180 W/E is Super Typhoon Genevieve (note this storm was a hurricane while in east and central Pacific Basins and is now denoted as a typhoon in the western basin); at 150 W is Hurricane Iselle, which is threatening the Big Island of Hawaii; and at 135 W is Hurricane Julio, which is trailing behind Iselle.

Active thunderstorms appear to have stayed just south of the Arizona border yesterday, as per plot of CG flashes detected through 09 UTC last night - above. The 13 UTC analysis of blended PW (below, from CIRA at Colorado State University) shows values of just over an inch in far southeast Arizona, with values around an inch or less over the eastern 2/3 of southern Arizona. There is a strong moisture gradient across the northern GoC and northwestern Sonora.

At 500 mb this morning, a weak, short-wave trough stretches from near Salt Lake City south-southwestward across southern California. The new NAM forecasts this morning keep this feature nearly stationary, while moving a weak, inverted trough northward along Baja. The chart above is the NAM forecast valid at 12 UTC tomorrow morning (August 8th).

Apparently in response to both the weak tough over Baja and several Mexican MCSs last night, both the NAM and GFS variants of Atmo's early WRF model forecasts indicate a push of higher, low-level moisture and increased PW into Pima County by 5 pm MST this afternoon (NAM version above and GFS version below). Both versions of the model forecast isolated thunderstorms to develop late this afternoon, in response to the increased low-level moisture, over central and eastern Pima County. This would be quite a change from conditions this morning - especially given the very low PW out in southwestern Arizona and the low-level westerly winds. Will have to check the 12 UTC WRF runs when they become available.

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