A Complicated Morning

Yesterday afternoon storms stayed to the south, without any activity in the immediate Tucson area. Several heavy storms occurred in central Pima and Santa Cruz Counties. The ALERT network had 4 sites in the far southwest with rainfall - 2 sites had over half an inch. Moisture has increased from the south and Yuma has a strong and ongoing moisture surge that began yesterday morning. The morning Tucson sounding appears to have decent CAPE for today. The models all forecast storms in southeast Arizona, but with heaviest storms again along the borderlands. There is a fairly sharp cutoff in the forecasts, with few storms north of the Catalinas.

The upper-level cyclone has weakened over the southern GoC and will open up and shift northward during next 48-hours. A pronounced, inverted trough at 500 mb will move across southeast Arizona this afternoon and evening. Steering flow is good and upper winds, though light, are nicely difluent. So, the ingredients coming together today appear to be the best combination of the summer.

At 6 am MST the tops of Cbs were visible to the south, and the TUS 6:30 am radar (composite display above) indicated substantial early morning shower activity. The morning showers and cloudiness will affect the model forecasts, and the important question is to what degree. The early WRF-GFS forecast of composite radar echoes at 6 am is shown below. There are definite problems with the extent and placement of the showers.

The 6:30 am visible satellite image (above) shows widespread and heavy cloudiness over northern Mexico and much of Arizona. The WRF-GFS forecast of OLR for 6 am (below) had much less cloud cover than was actually present - so heating will be reduced, or delayed, relative to the early model forecast. It will be interesting to see what the 12 UTC runs at Atmo produce.

The early WRF-GFS forecast of composite radar echoes (above - valid at 2 pm this afternoon, 3 July) indicates heavy storms over portions of eastern Pima County and along the border of Santa Cruz County and Mexico. I think that the best outlook for the day, at this time, is that the WRF-GFS early forecast will turn out reasonably accurate, but with timing of storm development delayed. I will be hoping for development further north also!

Finally, the early WRF-GFS continues to forecast that today will be the most active, with diminished storms and rainfall on the 4th and 5th, as the action shifts north and westward.