At 6 pm MST yesterday afternoon there was still little activity in the region affected by dry subsidence earlier in afternoon (see below). There was one small echo on the south side of the Catalina Mountains (inside elipse) and directly south of that echo, just across the border, was a much larger storm (arrow) that had been reported as severe at Rio Rico and probably at Nogales. Surface obs have not been available for Nogales since 4:25 pm yesterday, when a heavy thunderstorm was in progress. Nogales had received 0.51" of rain in 35 minutes and heavy rain continued when the site went down.
Later in the evening a number of storms developed oover the Tucson metro area, possibly above or around the edges of the dry dome (remember that given the same P and T dry air is more dense than moist air). With the very light flow aloft, the storms may have formed because of the earlier, mesoscale drying - a bit of a conundrum.
We had rain here at the house but only 0.10". Tucson airport had 0.64" and 49 of the 93 Alert gauges measured rainfall - about 55 to 60% areal coverage and up substantially from previous day.
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