Strong 500 mb cutoff over Oregon this morning (Wednesday May 18th) with main short-wave trough extending south aross California. Strongest vorticity maxima currently over southern Nevada and northern California coast, with vorticity tail extending north to Alaska. System most strongly impacts northern Arizona as it shifts eastward, with the vorticity tail strengthening and shifting southward to southern Arizona by Friday. Looks like windy and dusty conditions today, with pollen blowing around making for bad allergy conditions.
Paper this morning mentions 30% chance of rain tonight for the metro area, but this may be optimistic.
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Top graphic above is from the U of A Atmo WRF-GFS forecast run at midnight. Shown is composite radar reflectivity forecast for 6 pm this evening - this is about the maximum activity the model forecasts for southeast Arizona. Middle graphic is WRF-GFS forecast of total precipitation through noon tomorrow. With some slight amounts at higher elevations and to the north, the WRF forecasts zip for Tucson metro area. This morning's NAM (bottom), with its coarser resolution, smears some light precipitation into lower elevations - shown is total forecast precipitation through noon tomorrow.
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The only hopeful signs I see for showers are 1) there seems to be quite a bit of cloud and moisture spilling over the coastal ranges in northern Baja and southern California, and 2) the blended PW product for the eastern Pacific at 1200 UTC this morning (see graphic below) shows a very nice plume of higher PW coming into the Southwest. So we'll wait to see what this evening actually brings.
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