Thursday, August 11, 2016

Heavy Morning Rains Again?

Heavy clouds hanging on the Catalinas at 7:00 am MST this morning, as PW in lower half of troposphere remains very high. Could see some lightning flashes on north side of mountains while I was walking.

Yesterday provided the classic example of how difficult it is to predict convective events two and three days out - while the forecast POPs for yesterday (5:00 am through 5:00 pm) had been 80% for a number of forecast periods, the main event for the metro area occurred on Tuesday morning. Yesterday was mostly suppressed in eastern Pima County, with only 9 ALERT sites reporting light rains, mostly in the Catalinas. Plot of detected CG flashes for 24-hours ending at midnight last night shows fairly widespread thunderstorm activity for the state - there were some severe storms along the Utah border and also in Maricopa County.

This morning thunderstorms developed within the past few hours, over and north of the Catalinas. See Mike Leuthold's Day Two discussion from yesterday afternoon, since the WRF models were forecasting early am storms.Composite radar image above is for 6:40 am. ALERT rainfall below is for 3-hours ending at 7:00 am - with some heavy amounts on north side of Catalinas.

The 12 UTC morning sounding plot for Tucson (above, from SPC) is very much as forecast by the WRF models yesterday, with a very unstable situation with little lift needed for storms - there appears to have been a MAUL layer at sounding time between 700 and 850 mb. Will storms be triggered over the metro area this morning? Tough call, since the storms have generally been shifting slowly northward. However, there appears to be a weak outflow ( see MesoWest surface plot for 7:00 am below) moving southward toward western parts of the City - probably a coin toss or a bit better right now for rain at the house.

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