Monday, September 24, 2012

Last Week Of September Will Be Interesting

A short-wave trough at 500 mb is approaching Arizona this morning and will be moving slowly eastward. It appears from the model forecasts that this feature will weaken and stagnate over western Arizona. Middle level temperatures are col across the state and some convection is likely with this wave. The dewpoint temperature has jumped upward at Yuma ahead of the short wave - see current time series above. This morning's early forecast run of the Atmo WRF-GFS actually forecasts some isolated light showers and rainfall across southeast Arizona through midnight tonight see below.

Miriam (7 am visible image above) has likely strengthened to a Cat. 3 hurricane this morning, and may strengthen further. The current NHC track forecast below takes Miriam on a path that will trigger a surge of low-level moisture up the GoC. This initial impact of Miriam will likely occur 36 to 48 hours sooner than the GFS/NAM models indicate. I expect that the push of low-level moisture will be into southern Arizona during Wednesday night or Thursday morning. The key question then will be whether or not convective instability will be increased enough to support thunderstorms. By Friday and Saturday long-range model forecasts indicate that the remnants of Miriam will be affecting the Southwest directly. Thus, a very interesting week on tap.

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