Monday, August 31, 2020

Complicated Situation To End August

Very humid this morning after last night's light rainfall - cumulus are already forming on the Catalinas (above) before 8:30 am MST.

Plot of detected CG flashes (above for 24-hours ending at 01:30 am this morning from Atmo and Vaisala) shows that most thunderstorm activity remained well west of the metro area yesterday afternoon and evening. There were a couple of small cells near here though that produced some thunder and a light shower around 10:30 pm at house. Only 0.02" in the gauge this morning.

The ALERT network (northern portion below) data show that there were scattered reports and that two sites measured over half an inch. Amounts don't seem large enough, but there had been flow in the Rillito during the early morning hours. In the southern half of the network, Arivaca and Tubac gauges reported 0.04".

The 500 mb map above for this morning is from the Univ. of Wyoming weather page - the bad height at Chihuahua is messing up the analyses at other sites. There are several weak troughs over Mexico and the Southwest - one over western Arizona may be passing by today (note that in addition to the bad height at Phoenix, the wind speed seems a bit suspect too). The 500 mb temperature here is a warm -5 C, which is not too favorable for storms.

The morning TWC sounding (below) is wet with 1.65" of PW, and considerably more CAPE than yesterday. Steering level winds from 500 to 300 mb are west-southwesterly and fairly strong at 20 to 30 kt. The continuing west winds aloft are also not too favorable for storms, but the clear skies and unstable conditions may dominate.

The GEFS plumes for QPF at airport from the 06 UTC run (second below) are all consistent and forecast a distinct late night to early morning event tonight, and then little else during the week.

The early WRF forecasts that I looked at tended to keep most storm activity to our south and east. The NWS morning forecast indicates 50 to 60 percent chances of rain at the airport for today, tonight, Tuesday, and Tuesday night.

It seems a pretty mixed bag of signals this morning, and we'll just have to watch how all this plays out. However, I would hope to end the month, and also meteorological summer, with a nice amount of rain in the gauge tomorrow morning!

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