The Phoenix area had a nice, general rain event yesterday (above is Phoenix Rain Index plot for the 17th), note though that most of rain fell between midnight and 7 am yesterday morning. Below is the metro-west portion of the Pima County ALERT network for last 24-hours - there was almost no rainfall over central Tucson. The two decent amounts occurred in the west Catalina Mountain foothills - one heavy rain storm sat north of the house for almost an hour (that's the 0.87" amount). Areal coverage for entire network was a bit less than 60% - here at house we had light showers that added 0.02" during the afternoon - total for day 0.15".
The atmosphere over southern Arizona remains sopping wet, with PWs at lower elevations running from 1.75" to around 2.25" in the west half. The skewT plot of this morning's Tucson sounding is above (from the SPC). CAPE appears to have diminished considerably; I estimate just a sliver or so this afternoon at low elevations. Winds below 300 mb are essentially L/V, so mountain-slope storms will just drift around and have a potential to again produce local R+. Anvils will stream off toward the southeast in the stronger flow around the top of the 250 mb anticyclone, which is centered over Baja. The latest NAM forecast for 500 mb is shown below (valid 5 pm MST this afternoon). While the anticyclone is large, the winds are very weak, except down in central Mexico. Feature along east coast of Mexico is TS Helene.
Models have been over-predicting rainfall coverage for three days now - so what will today bring? There is a clear difference this morning between the NAM and early WRF-GFS precipitation forecasts. The 06Z run of the NAM predicts widespread rain across all of Arizona through midnight tonight (above). However, the early WRF-GFS predicts a substantial downturn across all of southern Arizona today (below is forecast rainfall through midnight tonight). What will it actually be? If I had to bet, I'd say something in between the two forecasts with a spatial bias toward higher elevations. We'll keep an eye out, and also check the 12 UTC WRF forecasts.
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