Early Morning Showers Still Around Metro Area

The above view shows the Catalinas shrouded in heavy cloud yesterday afternoon around 5 pm. Rains were heaviest in the metro area yesterday around noon to 2:30 pm MST - DM received over an inch from those showers and there were some embedded thunderstorms. Driving around north-central Tucson was a real nightmare around 2 pm yesterday, as the streets were essentially running washes. At 5 pm we had received a total of 0.65" here at house, but then there were more showers around 9 to 10 pm and heavier showers after midnight, through the early morning hours. It is still raining lightly and all I know about current amount is that it is over an inch. (Through 7:30 am MST this morning event total here at house is 1.72 inches.)

The plot above shows that CG flashes were very limited for the 24-hours ending at 12 UTC. There were thunderstorms ongoing at sunrise up in the Rim Country and also a heavy storm was moving through the east side of the Phoenix metro area. This has turned out to be quite some rainfall event, particularly in the Catalinas, which have received the heaviest rains here in southeast Arizona during the past 24-hours. The plot below shows 24-hour rain amounts over the Catalinas sector of the ALERT network at about 5:30 am - note two stations reporting over 3 and 4 inches! Across the entire ALERT network there was 100% coverage and an amazing number of stations (45, or approximately 50% of the sites) reported over an inch of rainfall for last 24-hours. Five sites had amounts over two inches.

This event has unfolded as a weak, 500 mb trough in the westerlies has interacted with the low-level moisture plume from Simon that covered most of Arizona yesterday morning. The remnant low-level circulation of Simon got hung up around the Baja spur yesterday, while the middle-level pieces sheared off to the northeast. The NAM 500 mb analysis at 00 UTC last evening (above) indicates two vorticity maxima within the broad trough over the Southwest. The one over northeast Arizona may once have been directly associated with Simon. The stronger maximum near Yuma has been moving across Arizona during the night, with bands of showers ahead of it - thus, the two distinct periods of heavy rains over the metro area and local mountains. Shown below is 00 UTC NAM analysis for 250 mb, with upper-level trough still back over central California.

The various model forecasts from 00 and 06 UTC forecast the early morning showers here reasonably well - as opposed to the first go-around at mid-day yesterday. The main part of the short-wave will be moving on out of Arizona by evening, but the possibility of at least isolated showers will remain until this trough is well past us.