Tuesday, July 29, 2014

Westerly Winds Dominate

Yesterday was almost totally suppressed  across southeastern Arizona, as was foreshadowed by the stable sounding yesterday morning. Chart above is 24-hour rainfall from MesoWest ending at 7 am MST this morning - July 29th.

This morning PW values across southern Arizona are around 1.25 to 1.50 inches; however, the early WRF-NAM forecast indicates some drying over central and eastern Pima County, with values falling to around an inch by 7 pm this evening (above). The forecast sounding for 7 pm (below) at TUS indicates almost no CAPE, as well as very light westerly winds through the troposphere. The model forecasts storms for the next two days to remain east and south of the Tucson area.

The main question I have about today's early WRF is whether it might be too dry locally. The forecast sounding for this afternoon indicates a BL mixing ratio of 8 g/kg. The morning sounding here has a residual BL with mixing ratio of 11+ g/kg. The only way that I can modify the observed sounding to get the forecast mixing ratio is to bring drier air from above 700 mb down into the BL. This may occur due to subsidence, given our proximity to the mid-level, southern lobe of the anticyclone. 

The new 12 UTC NAM forecast from the NWS seems to move some morning activity over northern Mexico into southeastern Arizona this afternoon. So all of this leads me to await the new WRF runs from atmo.

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