Friday, July 17, 2015

Storms Over Higher Elevations and Northeast Metro Yesterday

It was an interesting day yesterday with slow-moving thunderstorms and a number of outflows at lower elevations. Storms in the metro area were focused on the east and northeast parts of town. The plot of detected CG flashes above is for 24-hours ending at midnight last night (from Atmo and Vaisala). Although there were heavy storms in foothills and north side of Catalinas, the Rincons were relatively quiet. Mike Leuthold reported a downburst with strong winds and over an inch of rain at his place on the far northeast side just before six pm. Across the ALERT network 57 of 92 sites had measurable rains during the 24-hours ending at 6:00 am MST this morning. There were 12 sites with a half inch or more and Mt. Lemmon reported 1.26 inches, while Keystone Peak off to the southwest had 1.34 inches. Here at the house there were several different thunderstorms but only a brief, moderate shower a bit after dark that produced only 0.05".

This morning there is heavy cloud cover (second above view at 6:00 am) and light showers scattered around the area (composite radar just above is also from 6:00 am), with a couple of stronger storms in Pinal County to the north. Both versions of the WRF model run at 06 UTC forecast the morning activity fairly accurately and both also forecast the focus of today's activity to continue to the north and west across Pinal County toward Phoenix area.

Locally, we will struggle with worked-over low-levels and limited sunshine. The morning sounding from TWC (below) exhibits an onion structure, with cooled low-levels and a high cloud base around 600 mb. The CAPE analyses from SPC are probably far too optimistic. However, the sounding may not be representative of conditions across the region, so caution is required in today's forecast. If there are storms around the metro today, they will probably be late because of the reduced heating and be related to outflows mushing around. 

Finally, Hurricane Dolores is weakening rapidly southwest of Baja, however the storm's moisture plume extends far to the northeast and is responsible for the cloud cover over southeastern Arizona. Global models hint at another storm following behind Dolores later next week. The IR image below is for 1230 UTC this morning.

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