Wednesday, July 09, 2014

Postmortem Re Yesterday's "Big" Storm Event

While there were widespread storms and rain across Arizona yesterday, it certainly was not a significant severe thunderstorm day as anticipated in my morning post yesterday. I managed to ignore the comments I made a few days ago about how it was extremely difficult for the models to get the local scale details correct this time of year. It is totally ironic that I have an appointment to have my eyes checked and to get new glasses this morning. So what went wrong? First I'll compare the forecast sounding vs the actually observed sounding for last evening.

The forecast sounding for 5 pm yesterday at TUS is above and the observed sounding for that time is below.
The dry intrusion in middle layers was stronger than forecast and the the layer from the top of the boundary layer to 500 mb was warmer than forecast. CAPE was not as large as forecast by the model. Wind shear within the cloud layer did not become strong enough to support organized, large macrobursts.  So, these fairly subtle differences were all negative, regarding the character of the storms that occurred. Additional details that impacted storms over eastern Pima County were that storm anvils rapidly spread over the region and a cool outflow moved from the southwest across the metro area from 4:30 to 5:00 pm MST, stabilizing the local BL right after the sounding was taken. Totally buying into the models can be, at times, very much a double-edged sword.

There were widespread thunderstorms across the state (see CG flash plot above for 24-hour period ending at 3 am MST this morning - 9 July) and some of these were severe. There were a number of severe reports, mostly wind damage, sprinkled around the state (see SPC reports second below), and the large, intense storm near Casa Grande radar (immediately below from 7:40 pm) produced a nasty dust storm and apparently some wind damage in the southern Phoenix metro area.

The WRF runs forecast numerous mesoscale convective systems and outflows yesterday and had the general evolution of these essentially correct (above is IR image at 8:15 pm last evening and below is same for 3:15 am today). The winds however were over-done and the largest MCS moved from Cochise County southwestward into parts of Sonora, rather than forming over Maricopa County and moving westward.

And so it goes - reports of rainfall in a bit.

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