Thursday, July 29, 2010

Proposed New NWS Forecast Zones For Southeast Arizona

Yesterday - Storms yesterday were not quite as widespread as the day before. I thought that around 2:30 pm new cells were building in an excellent location to come across the house. I was busy for awhile and by the time I looked again around 5 pm, the cells I had observed earlier had totally crashed and there were new storms out to west and northwest. So, another day with no rain here at house. There was observed rainfall at 47 of the 93 Pima County ALERT gauges with heaviest amounts on the mountain paeks - 0.98" at Mt. lemmon and 1.61" at Manning Camp in the Rincons. Of the regular reporting stations, Nogales had a heavy storm and reports 1.00" in last 24-hours. Three high elevation RAWS stations had more than an inch, with Columbine on Mt. Graham reporting 2.33". Up in the Phoenix area there were some storms in the Valley, but PHX at Sky Harbor reported only 0.02" - giving them a total of only 0.06" since June 15th. Luke AFB had a heavy storm between 3 and 4 am this morning - however, their ASOS (I think?) precip gauge is bonkers and total rain is being reported as 36.81"!
Proposed New NWS Forescast Zones - The NWS proposes to change the southeast Arizona forecast zones this coming October. From their web page - the current zones (7 of them, with Tucson Metro being zone 33) are shown in the top image and the proposed zones (13 of them) are shown in the bottom image. The change breaks out the principal mountain ranges as separate forecast zones, which certainly makes sense wrt climate zones and weather. I think the elevation break is around 5,000 ft MSL. The Pima County ALERT gauges span a significant range of elevations and demonstrate the current challenges of forecasting for zone 33. There have been several events this summer when precipitation coverage was near 100% at higher elevation sites while there was 0% coverage at low, metropolitan gauges. The ALERT network has 47 gauges sited below 3,000 ft elevation and 46 are at higher elevations. During the past 24-hours 23% of the gauges below 3,000 ft had rainfall, while 78% of the higher elevation gauges had measurable rainfall. This should be an interesting change, come October.

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