Tuesday, August 14, 2018

Totally Suppressed Yesterday

The newspaper this morning reports the first drowning due to flash flooding this summer in metro area. The heavy storm Sunday afternoon/evening that moved from Vail toward I-15 (see previous post) flooded washes in that area. One car was washed away and the driver perished.

The southern half of Arizona was as suppressed yesterday as it has been in many weeks. Appears there was one lonely thunderstorm off in far southeast corner of the state. The plot of detected CG flashes above (from Atmo and Vaisala) is for the 24-hours ending at 7:00 am MST this morning.

The outlook for storms that would be marginally severe yesterday was definitely a bust. The TWC 00 UTC skew-T plot below shows that the well-mixed surface BL only built to about 800 mb - very shallow, and requiring considerable lifting to release the sliver of CAPE that was present. The PW held steady at about an inch and a quarter through the day. The thermal profiles seem to indicate several layers of subsidence above the BL, which led to the abrupt dissipation of mountain buildups during the mid-afternoon.

The strange upper-air pattern continues, as the mid/upper-level cyclone remains blocked over Kansas. Here in the Southwest the 500 mb anticyclone center has migrated to near the Four Corners (12 UTC analysis above from SPC). However, up at 250 mb (below) the center of the anticyclonic circulation is shifted far to the southeast, i.e., near Del Rio, Texas.

The TWC sounding, below, for this morning (skew-T and analysis from SPC) shows an increase during the night of PW, up to 1.65 inches, leading to considerably more potential CAPE than the evening sounding displayed. But the thermal profiles indicate that several layers of weak subsidence remain aloft. The BL will likely build to a deeper height today, but considerable lift will still be required to produce thunderstorms at low levels, because of very warm temperatures just above 700 mb. The wind profile is quite favorable for storms to propagate into the deserts.

The various WRF model forecasts available at this time indicate considerable and heavy thunderstorm activity over much of southeast Arizona - a better chance today for those marginally severe thunderstorms. Several of the forecasts continue storms well into the night, with MCSs reaching the Colorado River. 

Should be a much more interesting afternoon today for storm watching.

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