Monday, July 17, 2017

Very Active Period Continues

News was just breaking nationally yesterday evening: a flash flood produced by storms along the Rim swept away a family late Saturday afternoon. The family was swimming at a spot along the East Verde River near Payson when the flood swept them away, apparently resulting in 10 deaths.

Finger Rock peeking above stratus fractus this morning.

Storms did affect most of the metro area late yesterday, after dark and early am. Lightning and thunder here produced only 0.16", and amounts across the ALERT network were generally light over the City. There were 16 sites with no precip or less than 0.04" - these were across the east-central metro into the Rincons. Four ALERT stations had more than an inch of rain.

The heavy-hitting action was in the Phoenix metro with many severe thunderstorms and the first (I think) signifcant rain of the summer. PHX had 0.41", along with gusts to 62 mph. Detected CG flashes for period ending at 6:00 am MST shown below (from Atmo and Vaisala).

The morning sounding from TWC (plot above) is very moist with little CAPE and weak winds. The visible satellite image below is from 8:00 am MST. A mesoscale convective vortex has really helped spin up a circulation (off to our west-northwest) in the first inverted trough that moved by yesterday. It appears that we have clearing from the east and will get some significant sunshine.

Took a quick look at the 06 UTC WRF-GFS forecasts from Atmo. The model did quite well with the early morning activity and the sounding forecast for 12 UTC was quite good. By mid-afternoon the model forecasts significant storms again in eastern Pima County - composite radar forecast above is valid at 4:00 pm.

Rainfall amounts (below through midnight tonight) are quite large, with forecasts below indicating heavy rains from Santa Cruz County north to eastern Maricopa County. I noted that the forecast TWC sounding for 3:00 pm indicated that easterly steering winds had returned and that mixed-layer CAPE exceeded 2000 J/kg. Quite a forecast recovery. The model did get the 500 mb circulation this morning fairly accurately. So it may be on track again. With the thermodynamics that are in place, there would continue to be a threat for severe, wet microbursts.

Finally, the eastern Pacific continues very active - IR image below is from 14 UTC. Cat 3 Hurricane Fernanda is furthest west; looks like next system to east has already become TS Greg; and the third system near the Mexican coast is also forecast to strengthen.

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