Storms tended to keep to higher elevations yesterday - CGs for 24-hours ending at 5 am MST this morning show a relative minimum centered over Tucson. Across the ALERT network only 20 sites had rainfall, but there were 8 sites with more than half an inch and 3 with more than an inch (max 1.43" at Mt. Lemmon). Here at the house a storm developed nearly overhead and produced 0.17" of rain at mid-afternoon yesterday - and that light amount is, sadly, the most rain for any day this summer here.
The TUS morning sounding plot (above) shows a considerable decrease in PW (34 mm down from more than 45 mm yesterday) with an attendant decrease in CAPE. The time series of GPS PW (below) shows this intrusion of drier air - which has pushed across southwestern Arizona on low-level westerly winds.
The early WRF NAM run at Atmo forecasts a battle between dry and moist air today, centered over central Pima County. The forecast of 850 mb dewpoints is shown above for 5 pm MST this afternoon. But the forecast of composite radar echoes valid at 6 pm (below) indicates a small cluster of storms centered right over Tucson. So the model keeps enough moisture for storms here in eastern Pima County, but westerly winds could prevail and keep things relatively suppressed - will be interesting to see which air mass prevails. Cloud bases will be considerably higher than last several days and the model forecasts a strong gust front across metro Tucson with the storms.
Finally, a very large early morning MCS affected much of central US after midnight - water vapor image below is from 1315 UTC - couldn't resist showing this!.
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