Saturday, March 10, 2018

System Tonight Looks Wetter Than Expected

During the night forecast models have picked up the substantial moisture plume headed our way from lower latitude,s and become wetter for tonight's precipitation. The 13 UTC MIMIC TPW (above) shows values around an inch already creeping into southwest Arizona. The analysis also picks up two cyclonic circulations that are heading northeastward - one is near 26 W just north of 30 N and the other is near 133 W just south of 30 N.

The 1330 UTC IR satellite image below indicates how substantial the cloud/moisture plume is - extending far to the west-southwest and reaching below 25 N. The Yuma NWS radar (KYUX - second below) is already detecting light showers over southwestern AZ. Note - the small, bright red echo between Mexicali and San Diego is return from a wind farm just south of the border.

The model forecast plumes have also become wetter during the night - above shows QPF plumes for TUS from the 09 UTC SREF run and is from the plume-viewer at SPC. The spread is fairly large for tonight's event, ranging from a Trace to almost half an inch. The means are similar for both the GEFS and SREF plumes - around 0.15". Forecasts are basically for a light rain event at low elevations, but one with essentially 100% coverage.

The graphic below shows the changes in the plume mean for the last four forecast runs of the SREF (color code for run times at top right). The runs yesterday were quite dry, but the two runs after 00 UTC have become considerably wetter.

Finally, a look at a couple of forecasts from the 06 UTC WRF-GFs. Above is forecast skew-T for TUS valid at 06 UTC tonight. The sounding is forecast to be deeply moist, with over an inch of PW - very substantial changes between now and then. Below is model forecast of total precipitation through 06 UTC tomorrow morning.

Impacts for the Book Festival - much of which is outdoors along the University Mall - will be a damp and cool morning tomorrow, with perhaps some lingering light showers. Will showers develop before today's events wind down? That's a close call and we'll just have to watch.

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