Thursday, August 30, 2018

Outflow From Mexico Increases PW

Yesterday's 06 UTC WRF-GFS forecast of a large outflow pushing higher PWs into southern Arizona by midnight last night was very good. This morning there is a large band of sprinkle showers moving northward across portions of southern Arizona, including the metro area.

IR satellite image from 03 UTC last evening above captures the very large MCS over northern Mexico. This MCS generated the large outflow that impacted much of southern Arizona during the night. Plot of detected CG flashes (from Atmo and Vaisala for 12-hours ending at midnight last night - below) indicates that a few thunderstorms inched northward into Arizona. A number of stations recorded gusts over 40 mph and a bit of rain and sharp jumps in surface dewpoint - at the airport the jump was significant around 9:00 pm MST.

MIMIC total PW analysis at 12 UTC above indicates very high values of around 2 inches into Arizona between Nogales and Yuma - quite a change. This morning there is a large MCV spinning somewhere south to southwest of Nogales - need more visible images to locate it better. The IR image below for 1220 UTC shows a huge residual cloud mass left behind by the MCS.

The 500 mb anticyclone is small but centered off toward Albuquerque, giving us strong mid-level easterlies over southeastern Arizona (12 UTC analysis above from SPC). Large trough over the northwest will be pushing on the anticyclone as it (the trough) inches southward. The 12 UTC skew-T plot for TWC (below - from SPC) has PW over an inch and a quarter with a very good wind profile for organized thunderstorms. However, with limited heating there will be little CAPE at low levels and that will have a significant capping layer above it. The current WRF forecast runs have mostly isolated mountain storms for late afternoon - which seems reasonable to me.  

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