Thursday, August 03, 2017

Anvils Yesterday - Today Another Tough One

Virga at sunrise today - view is looking due south from Tucson at Prince (north side of city).

Yesterday was another down day for the metro area, as storms to south covered city with anvils by noon. A few spits of rain here early afternoon from thick anvil and that was it. Detected CG flashes above (from Atmo and Vaisala) and ALERT precipitation below - both 24-hours through 7:00 am MST this morning. Heaviest storms were to south and west of the city. Most intense thunderstorms were again along the lower Colorado Basin, with severe reports from Yuma to Las Vegas yesterday afternoon.

The large trough over eastern U.S. has continued to cause some shifts in the pattern over the West. The 200 mb anticyclone has shifted southward to northern Mexico - which is good. But the 500mb anticyclone remains an ambiguous mess. The height field is very flat, but winds indicate the anticyclone center remains over the Great Basin.

The morning sounding data at TWC remain very moist (PW = 1.84" - as per sounding plot above from SPC). But very light winds continue below 300 mb. Potential CAPE with heating is substantial and storms should be active again on mountains. The positive aspect of the sounding has resulted from the southward shift of the upper-level anticyclone - this has resulted in winds aloft that will push anvils back toward east-northeast. This leaves better chance for some developments at low elevations due to outflows.

The morning sounding at El Paso shows PW of only 0.93" (about half that at Tucson) and east winds in the drier air below 500 mb - so key question today will be how far into Arizona the dry air advances. The visible image (below from 7:00 am) seems to indicate that the moist air extends at least to New Mexico border. At upper-levels (above 300 mb) dry air is moving across state from the southwest - a situation of double jeopardy.

Last night's WRF-GFS forecasts indicate a very significant dry-out covers the state by the 5th. As for today, chances look improved for some storms to move into lower elevations, unless the dry air pushes in from east more quickly than WRF forecasts indicated last night. Will be watching for the 12 UTC WRF forecasts and Mike's discussion.

1 comment:

  1. For such large dry-out forecast here, the actual dewpoint forecasts and reality are both minor...65 down to 55 to start the day? Still big cumulus out my windows, and a 49F dewpoint. "We'll see". Same anvils here since it stopped with the every other day downpours.

    Your earlier posts showing how green it is (Cochise County?) isn't far off Las Cruces, especially by the mountain where there is more desert grassland cover.

    Summer storm chasing the southwest...the guy must be let down compared to spring on the southern plains!