Sunday, October 07, 2018

Unsettled Day Unfolding

Strong and cold closed low southwest Utah and northwest Arizona has brought thunderstorms and precipitation amounts of half to around an inch - this over northern 2/3rds of state. Flagstaff has had its first snow of the season, as per view above of the San Francisco Peaks at 7:18 am MST.

Visible satellite image from 7:00 am above shows heavy cloud cover over northern half of state, with several cloud bands trying to build south toward our area. Plot of detected CG flashes for 24-hours ending at 7:30 am (below, from Atmo and Vaisala) indicates abundant thunderstorm activity during the night. Currently, storms have reached across much of Pinal County and are trying to build on into parts of Pima County.

The 12 UTC 500 mb analysis above shows the closed low with core temperatures of around -20 C and very strong winds over Arizona and California to south and rear of system. Morning sounding for TWC (below from SPC, as is 500 mb analysis) indicates very strong winds aloft that reach speeds of around 90 kt at 250 mb. The strong jet will pull the closed low a bit further south before it heads for Four Corners Region tonight.

The WRF forecasts continue to be a mixed bag this morning: the NAM version remains fairly dry for eastern Pima County; but both the GFS and RR versions forecast a narrow band of storms later this morning, that is followed by strong evening storms. The 12 UTC WRF-RR is currently the strongest and wettest forecast for metro Tucson.

Interesting weather through tomorrow morning, and then we'll have the remnants of Sergio trying to bring another precipitation event to our area by end of coming week.

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