Saturday, July 11, 2015

Dry VS Moist Air Flows Again Today

I have been involved with other issues and have not been able to post since last Monday. Was certainly a quiet period as the thunderstorm activity stayed mostly in higher elevations of the eastern third of Arizona. Around 10 percent of the ALERT stations had rainfall each day this week - Monday - Thursday and yesterday was the first day with zero coverage in the network.

The 12z sounding plot for the TWC upper-air data (above) shows a sounding that continues to look more like a September transition day than the 11th of July. There is 1.50" of PW, considerable CAPE, and a severe thunderstorm-supporting wind shear profile. But, again the issue becomes that of whether drier air will move in from the west this afternoon. The blended PW analysis for 12 UTC from CIRA (below) indicates the moist air mass over southeast Arizona, but with a substantial gradient lurking out west in central Pima County. The morning PW amounts from GPS go: Tucson 1.50"; Tohono O'odham Community College 1.25"; Organ Pipe National Monument missing in action; and Yuma 0.75". The WRF model forecasts from both versions at 006 UTC indicate BL winds to become westerly this afternoon and dry out the low-levels to some degree. Both models keep thunderstorms off to the east and northeast again today.

Meanwhile, to the south there is a developing tropical disturbance off the south coast of Mexico. This will likely become a hurricane in the next several days and head off to the northwest - large variance currently within model forecasts as to how close this storm will come to the southern tip of Baja. The NHC morning outlook for today is shown above, while the IR image below shows the system at 1315 UTC this morning. Looks like this system is also out of the gates more quickly than is NHC. 

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