Wednesday, August 22, 2018

Mexican MCS Shuts Us Down

The extreme rains and flooding in south-central Wisconsin that occurred Monday have been in the news. We were in Madison, Middleton, and that general area two weeks ago, and are certainly glad to missed out on this event.

The large MCS over Sonora left behind a significant MCV, and attendant cloudiness, that moved north over our area during the day - lack of heating and very light sprinkles keep things cool and stable for most of day. We had a sprinkle Trace here and the entire ALERT network was void of rainfall observations except for three sites in the southern portions of the network. The map of detected CG flashes above (from Atmo and Vaisala, for 24-hours ending at 5:00 am MST this morning) shows that lower elevations of southern Arizona were essentially totally suppressed yesterday wrt thunderstorms. 

The anticyclone at 500 mb (12 UTC charts and skew-T plot from SPC) has continued to shift eastward and southward and is now centered over southeast Texas. Cyclone over the Northwest has moved far enough south to swing winds around to the west at 500 mb and above over most of the Southwest (see also 250 mb chart below).

The morning skew-T plot for TWC (above) remains moist and with considerable potential CAPE - clear skies to our west and southwest should lead to a much deeper BL this afternoon (7:00 am visible image below). The vertical wind profile, however, continues to be a mess: L/V below 800 mb, nice southerlies 800 to 600 mb, and then weak westerlies to 300 mb. Main take from all of this is that any storms that do develop today will be slow moving. Drier and warmer air from the west will be advecting our way, so that some capping may develop.

The WRF runs from 06 UTC forecast only popcorn storms over central and east Pima County this afternoon, but both versions again forecast substantial thunderstorm activity nearby after midnight. In contrast, a quick look at 12 UTC WRFRR reveals that that version of model forecasts strong storms over eastern Pima County by late afternoon, but only a bit of nocturnal activity. Will await Mike L.'s discussion regarding details of the model forecasts.

Another difficult forecast day, as are most here in summer, except when we are experiencing a dry out period.

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