Chaotic Skies At Sunrise On July 2nd

Skies were chaotic this morning with middle clouds and cirrus (view above is to north of Kitt Peak) - essentially debris from yesterday evening's convection over far southeast Arizona and northern Sonora. The convection fizzled by 10 pm or so, thus no outflows of significance were running around during the night.

There was a lot of altocumulus castellanus out to the west this morning. These were showing up on the KEMX radar as 10 to 20 dBZ echoes. However, the KIWA radar was indicating strong, 50 to 60 dBZ echo - see 1400 UTC composite above. The radar loop indicated these to be ground clutter echo. Apparently the new dual polorarization upgrade is not working well in sync with the clutter filters. There appear to have been some small areas of rock rain accumulating to 1/2 an inch or so. (Edited to add - Paul I. has alerted me that there is no clutter filter operating right now on the KIWA radar. So, until this situation is corrected beware of unusual strong echoes, especially in the early morning hours.)

This morning PW values over southeast Arizona are around 1 inch. The Atmo WRF-GFS model continues to bring moisture from the east-southeast today, followed by a very strong Gulf Surge tonight and tomorrow. This surge brings PW values of nearly 60 mm into the lower Colorado River Basin (Tucson gets just above 40 mm tomorrow afternoon). The surge is forecast by most of the models to push into Southern California and northward up the Colorado toward Kingman and Las Vegas - leaving the Tucson area on the eastern fringes of the weekend storm activity. The WRF composite radar forecasts (see above for 2 pm on Sunday the 3rd) indicate that early tomorrow afternoon would be the most active period around Tucson. The WRF does forecast a strong to severe MCS developing west to northwest of Tucson tomorrow, and that it will push westward across the Colorado and into southern Californina on Sunday night.

Finally, the WRF continues to forecast the bulk of rainfall over the long weekend will occur from northern Sonora northwestward toward Las Vegas. Graphic above is total accumulated rainfall forecast from this morning through 11 pm on the 4th. Of course we'll just have to wait and watch as the smaller-scale details of the weekend weather evolve.