Sunday, August 23, 2020

Close But No Rain Here Yesterday

Chaotic skies last evening, but with no storms threatening the metro. Only severe reports were far out to the northwest around Chino Valley, north of Prescott.

Down at bottom is current forecast from NHC for developing hurricane Marco, which is forecast to make landfall over southeastern Louisiana tomorrow morning.

IR image above from about 9:30 pm MST last evening is impressive, with MCS covering Cochise County and just nipping extreme eastern Pima County. Plot of detected CGs (below for 24-hours ending at 1:00 am this morning - from Atmo and Vaisala) shows thunderstorms reached just into eastern Pima County. Over most of Pima County (and southwestern Arizona) the large scale subsidence appeared to dominate local lifting. Outflow at TUS and DM reached 40 pm from the east, but did not force new storm developments.

Rainfall reports here for 24-hours ending at 6:00 am this morning - above from the ALERT network and below from MesoWest. Heavy amounts around the Rincons and across Cochise County, where two sites had over an inch of rain (Rucker and Canelo).

The 500 mb chart this morning shows that the anticyclone has shifted to near the Four Corners and that winds are not nearly as strong as they were yesterday over southern Arizona. The bad heights at Phoenix and Chihuahua continue to negatively impact the height analyses.

The 12 UTC sounding from TWC (above) continues to have significant CAPE, although the vertical wind profile has weaker speeds today, and not nearly as favorable vertical shear as was present yesterday. Steering winds are a bit jumbled, but will likely be from the east-northeast at about 15 kt. Anvils will spread south of any storm cores that develop. It appears that afternoon heating should trigger storms. 

The forecast below is from the 12 UTC WRF-RR and indicates strong to severe storms in eastern Pima County at 8:30 pm this evening. I looked at the 06 UTC WRF-GFS and it forecasts nothing at all in our area - so quite different results from the model forecasts - I'll root for the RR below.

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