Some Sunrise Storms - 4 August 2013

Yesterday was very suppressed in the general Tucson area, with afternoon storms out to the west in central Pima County. Nothing here and 0% coverage across the ALERT network at 6 pm. But early morning storms have brought some rain to the eastern part of the network - 11 stations (12% coverage) have reported rain in the last 24-hours (Manning Camp in the Rincons had 0.39"). First thing I saw when I got up early was a lightning flash off to the east-northeast.

Several MCSs in west and north Mexico during the night, with outflow from one that dissipated south of Cochise County apparently kicked off the early storms - mostly east and south of the metro area. The composite radar chart from the TUS Doppler is from 6 am MST.

The morning storms will cause problems during the day, making the forecast quite difficult. I have looked at Amo's early runs of both the WRF GFS and WRF NAM. The two forecasts are very different. The WRF NAM (not shown) forecast no early storms or rain, so it has immediate problems. It does forecast mid-to-late afternoon storms mostly to the south and then, interestingly, forecasts another round of storms tonight after midnight. The WRF-GFS forecast development of the early storms (above is forecast composite radar valid at 7 am MST); however, the location and extent of the storms seems off. The GFS also forecasts a very significant outflow from these storms (10-m winds valid at 7 am shown below). This outflow serves to stabilize things over eastern Pima County, so that afternoon storms are suppressed in the forecast.

Above is the WRF GFS forecast of rainfall through noon today and it shows that the heavy rains to the southwest of Tucson generated the large mesohigh and strong outflows. The GFS version of the forecast does not forecast storms after midnight, except down in Mexico. So too very different model outlooks for the next 24-hours. The 7 am radar data indicate new storms developing southwest of Tucson and also over Cochise County - so the GFS definitely has a better forecast for the morning.

The 12 UTC skew-T plot for the TUS upper-air sounding is shown below. More moisture present this morning, as well as some elevated CAPE. Steering winds are from the south at 10 to 15 kts, with fairly strong winds in the upper-troposphere. So another day where the forecast is not obvious, except for its complexity.