Another Marginal Day For Storms

Yesterday was indeed a bit of a zig-zag day for the models, with storm activity way down from Wednesday. Here at the house we were looking at mostly anvil cloud, although a couple of storms tried to go up beneath the high cloud. We had thunder and several sprinkles of rain, so another Trace day. None of the NWS sites or RAWS sites in southeast Arizona had measurable rain. Only 16 ALERT stations had rain (about 15%, down from nearly 40% the day before), and all but one site had less than 0.15".

The morning Tucson sounding plot from Univ. of Wyoming is shown above. There are winds stronger than 10 kts below 300 mb but the shear profile is not very good. Note that afternoon cloud bases would be up around 600 mb and winds above cloud base will tend toward uni-directional from the east at about 20 kts - this according to the early run of the Atmo WRF-GFS. There is only a sliver of CAPE indicated and low-level winds are also from the east.

The WRF-GFS surface forecast for 3 pm this afternoon is shown above. Note that surface winds remain easterly and dewpoints are down around 50F. So, mostly hot and dry today.

Finally, I'll show theWRF-GFS forecast of composite radar reflectivity valid at 3 pm this afternoon. This is as active as it gets in the forecast, with only some light thundershowers out west in central Pima County. Note that any storms that do develop will have the potential to produce downbursts, because of the high cloud bases.
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PS - All weather attention this weekend will of course be upon Hurricane Irene.