A very complex synoptic situation for northern Mexico and the Southwest this morning (Monday, July 2, 2012). The NAM 250 mb analysis for 12 UTC indicates that the upper-tropospheric cyclone has moved westward and is centered near the southern end of the GoC. (Subtropical upper-cyclones and inverted troughs exhibit maximum vorticity well above 500 mb, while tropical waves [aka easterly waves] exhibit maximum vorticity below 500 mb.) As the upper-level cyclone approached the GoC last evening, a large MCS devolped on the east slopes of the Sierra Madre Occidental and eventually decayed over the lower and middle GoC. This has helped push moist, mT low-level air northward up the GoC and west slopes of the Mexican mountains. The NESDIS blended PW product (below) indicates that values of 50 mm or more have reached to the northern GoC this morning.
The early run of Atmo's WRF-GFS model forecasts PW to increase slowly today (the forecast for 9 pm is shown above), reaching to near 40 mm over the Tucson area. The forecast TUS skewT for 6 pm (below) indicates decent CAPE and fairly strong easterly steering flow around 500 mb. The boundary layer, with west-northwest winds, is very deep, extending above 700 mb. Upper-level winds are light, but quite diffluent over southeastern Arizona.
The WRF-GFS forecasts the most active storms for the borderlands this afternoon and evening, but the forecast composite radar chart for 9 pm this evening indicates some storm activity over eastern Pima County. The model forecasts increased activity tomorrow, and then a shift of the activity toward the north and west of Tucson on July 4th. We'll watch things day by day, as this promising situation evolves.
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