Wednesday, September 13, 2017

Transition Pattern Sets Up Tonight And Tomorrow

Running late this morning.  Of note was the record high of 106 F recorded at the NWS ASOS site at the airport.

The 500 mb cyclone is located just southwest of San Francisco this morning at 12 UTC (analysis above from SPC), and was again associated with widespread thunderstorm activity yesterday from central California  eastward across the Great Basin. Forecast models  finally kick this feature eastward and this morning's 12 UTC NAM forecast of the 500 mb below is valid at 5:00 pm tomorrow afternoon. By then the wind profile will have become southwesterly and strengthened considerably, producing a classic transition pattern for Arizona.

The key forecast question will be how much moisture and CAPE can develop ahead of the short wave. Above is this morning's 12 UTC WRF-NAM forecast of PW valid at noon tomorrow. With PW remaining near and just over an inch, some cooling at 500 mb could lead to CAPE and fast-moving thunderstorms over parts of southeastern Arizona tomorrow.

The morning outlook from NHC for next 5 days (below) indicates considerable activity over eastern Pacific, but long range forecast models are very divergent re where any tropical storms that develop might track.

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