Friday, July 30, 2010

Big Storm Events at Both Phoenix and Tucson Yesterday

Both major metro areas in Arizona were hit by significant storms. Yesterday afternoon (July 29th) the storms that formed west and northwest of Tucson rolled down the Santa Cruz River valley with a strong outflow and dust. Another outflow came south from the mountains north of Phoenix and the two collided over Phoenix, producing strong new storm development over the city. There was widespread wind damage in the metro area, and Art Douglas, who was there, reports chaos at Sky Harbor airport from 3pm well into the early nighttime. The top two images show rain and downed trees in Tempe, and the SPC storm report map for yesterday (the points plotted around Phoenix don't really convey the extent of the event up there). I will check out the Phoenix Rainfall Index maps later this morning.
Here in Tucson, storms avoided the city during the afternoon, but the last round of storms developed late, as several had predicted yesterday, and moved across the metro area just before and after midnight (e.g., the Atmo weather station on campus recorded 0.69" before midnight and 0.29" after midnight). Here at the house the heaviest rains seemed to occur just before midnight, with rumbling thunder and quite a bit of mostly in-cloud lightning. There was 1.33" in the gauge this morning; the first summer storm event here at house with an inch or more rainfall since August 31st, 2008. At 6 pm last evening only 20 of the 93 ALERT gauges had gotten rainfall during the past 6-hours, but this morning 80 of the 93 gauges had measured rain during the past 24-hours - so a very widespread event, finally. Six of the ALERT gauges had more than an inch of rain; DM AFB had 1.17",and three of the RAWS gauges had more than inch. So, much welcomed widespread and significant rainfall in the Tucson area.
When I walked, just after sunrise, this morning the air was pleasant and filled with the smells of the rain, mixed with those of many desert plants - a wonderful morning in the low desert! I didn't see any evidence of strong winds in this part of town. But I saw that the spadefoot toads had emerged last night - several active in large puddles and more run-over in the streets. The final showers were still in view, with a sunrise rainbow out to the west. The Rillito had flowed during the night, but the very dry soil soaked up the water very quickly - see bottom graphic that shows flow at the USGS river gauge at Dodge Street (about a mile or so from the house). Flow spiked quickly to about 1300 cfs right after midnight and just as quickly fell right back to zero. The only negative impact of the rains I observed this morning were large swarms of flying ants and/or termites out in force.

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