Saturday, January 21, 2017

Wind, Heavy Precipitation Some Spots, And Some Lightning And Thunder

The current weather event blew through very quickly and has mostly ended for Pima County, much earlier than forecast. When I went for newspaper, at 04:30 am MST this morning, stars were out and only a few clouds were scudding by. The time series above is from Atmo for T and Td (vertical grid is in 5 F increments with top line of grid being 60 F) - it shows the event occurred in two distinct segments (three if you count the light showers at sunrise yesterday). Showers produced light, but measurable rains from around 07:30 to 08:30 pm at Atmo. But the main event occurred as the cold front approached and passed through eastern Pima County, beginning a bit after midnight and continuing until around 03:00 am. This morning's TWC sounding and the 06 UTC WRF-GFS forecast indicate a continuing chance for some light showers this morning.

The regional radar chart (below from NCAR RAP/RAL) is for 01:05 am and shows strong echoes moving through parts of eastern Pima County - DM AFB reported thunder, heavy rain and gusts to 56 mph at about 01:15 am. As I usually point out - this NCAR radar product is built using the KIWA and KEMX base scans, which reduces its representativeness, because of the serious terrain blockage around KEMX (Tucson radar).

Graphic that is second below (from and Vaisala) shows CG flash density for the 12-hours ending at 05:30 am this morning. Most thunderstorm activity occurred over south-central Pima County. Although none were reported to SPC, it is likely that a few storms right along the front were severe due to convectively enhanced wind gusts.

The two panels here show ALERT rainfall (top is northern portion and bottom is southern portion) for 24-hours ending at 05:00 am this morning. Redington Pass and the northwest flanks of the Catalinas had heaviest rain amounts that were well over an inch. There was a strong precipitation gradient, as forecast by Atmo's version of the WRF-GFS, from southwest of the airport northeastward to the Catalinas. The WRF-GFS forecast for the airport was far superior to that from the GEFS ensemble system, which considerably over-forecast the event at the airport.

Here at the house we had 0.58". The airport reported only 0.25" and DM had 0.33". Art Douglas reports 2.67" early this morning, but no snow, at his place in Ash Canyon - Carr RAWS just up to his north reported 2.16". Snow amounts unknown at this early hour.

Wind gusts of 40 to 50 mph were common - some higher gusts I noted were: Muleshoe Ranch and Gutherie RAWS sites had 67 mph, while Pioneer Airfield reported 58 mph. 

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