Friday, August 28, 2020

Stormy Weekend Possible

Contrast the dirty skies here in the city with the sparkling skies over Summerhaven this morning.

The current 500 mb chart (above from SPC) shows that the anticyclone has shifted some and is now centered over southeastern New Mexico. There are southerly winds over Sonora and Arizona this morning. Note that there is a strong temperature gradient at 500 mb, with Empalme reporting only -2 C and Tucson having -9 C. So there may be some warm advection aloft. But the height of a mid-level inversion is at play also - inversion is above 500 here but right at 500 at Empalme.

The morning sounding from TWC (below, also from SPC) has some CAPE in middle levels, but amounts appear well below 1000 J/kg. Steering winds are a bit uncertain, with the southerlies turning toward the west above 500 mb - and neither direction is very favorable for storms at low elevations.


The presence of both tropical depression Hernan (currently decaying at the south end of the GoC), and also tropical storm Isella southwest of the end of Baja, will help to push higher moisture contents north into southern Arizona. These PW forecasts are from the 06 UTC WRF-GFS run at Atmo. Above is valid at 5:00 am this morning and below is valid at 5:00 pm tomorrow afternoon. Note the strong push of PW amounts over 2 inches into Arizona!

Forecast plumes for QPF at the airport (above from 06 UTC GEFS) indicates significant storms late tomorrow into Sunday morning. Average forecast amounts reach to nearly an inch. The ensembles also forecast a significant cool-down (below), with high temperatures down over 20 degrees - this would be some wonderful relief from our blistering August heat.

Forecasts of composite radar echoes here are from: 06 UTC WRF-GFS above, valid at 4:00 pm this afternoon, indicating another day with isolated storms for our area; but forecast below - from this morning's WRF-RR indicates much more thunderstorm activity over our area at 7:00 pm late tomorrow. 

Hopefully it will be an active and interesting weekend.

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