Wednesday, September 05, 2018

Strange Day Today

Low-level moisture did persist yesterday and thunderstorms actually were bubbling up on higher elevations by 10:00 MST or so - very early start. I took these two photos around 11:00 am - storm on Catalinas above and mini-storm over Tucson Mountains below. The Tucson Mountain storms drifted our way with thunder before noon here, and a light shower produced 0.02". 

The plot of detected CG flashes (second below from Atmo and Vaisala) is for 24-hours ending at 1:00 am this morning. Storms mostly hugged the higher elevations, with the Tucson Mountain storms being the only activity within the usual Tucson donut hole. Across the ALERT network 23 sites (northern and southern portions of network) measured mostly light rainfall - but four sites had over an inch of rain (three in north end of Catalinas and one on west side of Santa Ritas).

Things are a bit strange today. For some reason there was no sounding available this morning from TWC. The PW appears to be continuing right around or a bit more than 30 mm. At 500 mb the last small trough within the chaotic large scale pattern will be moving across southern Arizona today, with southwesterly steering winds ahead of it. The 06 UTC WRF runs were available, and both versions forecast TWC mixed layer CAPE to be more than 1000 J/Kg around mid-afternoon. The GFS version keeps storms mostly to the east and south, with a couple of isolated storms in eastern Pima County. However, the NAM version forecasts significant storms over the metro area - above forecast of composite radar echoes is valid at 4:00 pm this afternoon. The model develops a large and strong outflow boundary that moves northwest from higher elevations in Cochise and Santa Cruz Counties - the outflow forces new storm development right over the metro area. Forecast below is 10-m winds, also valid at 4:00 pm.

The 12 UTC WRF-RR is also available, and it forecasts storms only across southern portions of Santa Cruz and Cochise Counties.

Depending on which model one chooses, our day today could be active, or have only some isolated storms in sight, or be very suppressed. My feel is that the NAM scenario is unlikely, and that GFS is probably more inline with what we'll see later today.

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