Saturday, July 05, 2014

Storms Severely Suppressed At Low Elevations Yesterday

Yesterday, as is often the case after an active storm day, was very suppressed at low elevations, with the forecasts yesterday being overly optimistic. The CG flash activity is shown in the previous post and the above plot of 24-h rainfall from MesoWest shows that storms in southeast Arizona stuck mainly to the mountain slopes. Storms that tried to move north toward the metro yesterday afternoon rapidly crashed as the moved into lower elevations. At 7 pm last evening only 24 sites in the ALERT network had measured rain during the day. These sites were in the Catalinas and off in the far south part of the network. Of note were the heavy rains (2 inches plus) up in the northern Catalinas for the second straight day. The plot below for the ALERT net over the Catalinas shows 48-hour rainfall as of 7 am MST this morning (July 5th) with a couple of stations approaching 4 inches.

Here at the house we had a Trace from some spits as cloud debris passed overhead from the south around 5 pm and that was it. No lightning or thunder here. Across the ALERT network 6 additional sites measured rain during the night. 

Today appears to be setting up quite differently. The 12 UTC TUS skew-T (from SPC above) shows the pronounced cool surface layer is gone - although there was shallow outflow from showers to the south. The PW is an impressive 1.72 inches and the analysis indicates a fair amount of CAPE. There are almost no steering winds present in middle levels. So, we have a fairly obvious situation that can support very heavy rains and wet microbursts, with only a small amount of sunshine breaking out. The 500 mb chart (not shown) indicates some cool advection is possible in middle levels this afternoon. The forecast models are very WET in their forecasts for today, so they may be a bit more accurate today than was the case yesterday (note that early WRF-GFS forecasts 0.60" at the airport by midnight).

I am optimistic that we might get a substantial storm here at the house today, since the situation would tend to support storms drifting from the south flanks of the Catalinas into the north part of town.

The visible satellite image from 7 am MST (below) shows a widespread area of clouds that stretches north into parts of California, Nevada, Utah and Colorado. Certainly an impressive push of moisture into the Southwest for early July. TS Douglas is still spinning west of Baja. There was an extended, and fairly strong, inverted trough around 500 mb associated with Douglas that swung across northern Mexico and Arizona the past two days. This feature apparently combined with Sonoran MCSs to push the mT air from the eastern Pacific and GoC far north into the Southwest. Note that this morning dewpoints are highest up the lower Colorado River Basin with Tds of 60 extending up to Las Vegas, Nevada. So, another interesting day on tap today.

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