Thursday, June 22, 2017

Moisture Up Some/Temps Down A Bit

Extreme heat (115 F yesterday) and more wildfires, with homes lost, around Sonoita dominated the news yesterday. Moisture from the GoC has gradually increased due to the persistent heat low and typical diurnal wind circulations - the WRF forecasts had indicated this several days ago. The 500 anticyclone is centered just off to the northeast and it looks to be another grim day for southeast Arizona and much of the Southwest.

Had a power surge here - probably as demand increased rapidly as people got up to 90 F temps - and have just gotten PC back to life. Will take a quick look at soundings this morning. The 12 UTC skewT for the TWC upper-air sounding is shown above. The increase in moisture shows up below 750 mb - also in T trace. Residual boundary layers (BLs) seem to reach well above 500 mb. When I estimate the afternoon BL, I see just a tiny bit of CAPE over low elevations.

Below is forecast TWC sounding from Atmo's 12 UTC WRF GFS forecast run valid at 04:00 pm MST this afternoon. The model forecasts a surface-based BL to reach only to about 700 mb with well-mixed moisture at 8 g/kg. That is overlain by a hotter, drier, elevated BL - apparently from higher elevations to our north, as per the winds in that layer - that significantly caps the surface BL. 

The questions is whether or not the two BL structure can actually persist today. I think that a well-mixed surface layer with 8 g/kg is probably quite unlikely - something closer to 6 seeming more likely. Thus, the afternoon atmosphere may be one in which the two BLs of the forecast have merged into a single, deep BL that reaches to around 500 mb. This would lead to build ups around highest mountains and more evening cloud debris over the deserts.

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