Saturday, July 07, 2018

Iffy Day Today - Inverted Trof Tomorrow

Main weather news has been the extreme heat in California, winds, and numerous wildfires burning across parts of the West.

I felt inspired to do a subjective 500 mb analysis for 12 UTC this morning and result is above. Main anticyclone center is north of Grand Junction, Colorado, with a smaller center off to east over Missouri. The anticyclone is huge and 500 mb heights are right at 6,000 m at core of the high over northwestern Colorado. There is a weak trof separating the two centers, as well as a weak short wave coming down east side of high. These apparently consolidate some and merge perhaps with the inverted trof that is somewhere over the northern Mexico data void. Regardless, models forecast a well-defined,middle and upper-level inverted trof to move westward tomorrow along the Borderlands. As for today, it appears that cooler air at 500 mb will move over southeastern Arizona this afternoon as per the -4 C at Tucson this morning versus -8 C at El Paso. Moist air has circulated, at 500 mb, all the way around the west side of the anticyclone from southern California north to Montana.

Plot of 24-hour CG flash density (from and Vaisala - above thru 14 UTC this morning) shows there were thunderstorms over northwestern third of Arizona yesterday, but that much of Arizona, New Mexico, and northern Mexico was suppressed.

The 12 UTC skew-T for TWC (below from SPC) indicates little CAPE again at Tucson, even though PW is up over an inch now.

The 06 UTC WRF-NAM is the most aggressive of the local model runs from 00 and 06 UTC. Most forecast some isolated buildups and virga/sprinkles possible for eastern Pima County this afternoon. The forecast TWC sounding from that run is shown above, valid at 4:00 pm MST this afternoon. The model has developed CAPE, largely due to forecasted cooler middle-level temperatures. Winds have weakened both in low and upper levels, leaving a shear profile that, if storms develop, would leave anvils trailing behind convective cores. The model forecasts a fairly organized arc of composite radar echoes (below, valid at 6:00 pm this afternoon) to move across Pinal and eastern Pima Counties. Looks like another day where big challenge is to determine which model runs are most likely to verify this afternoon.

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