Thunderstorm and light shower activity increased some yesterday, and there are early morning showers to the east in Cochise County (see 8 am MST visible image above). The early run of Atmo's WRF-GFS model picked this up nicely. The increased shower activity has recycled some moisture into our deep boundary layer, and the 500 mb cutoff that is over southwest Arizona and northwest Sonora has help pull some middle level moisture northward across the border. Interestingly, this morning PW is higher across southern Arizona than it is at Hermosilla, Mexico. The 500 mb cutoff is digging to the southwest and will sit off of northern Baja for the next two days, before perhaps heading back across the Southwest as a weak, open short wave.
The GPS time-series of PW (above, with TWC raob values plotted) shows the nice increase here at U of A, with PW nearly doubling from noon to midnight yesterday. Values are now over an inch across southern Arizona - in contrast, Hermosilla is at about 0.75".
This morning's Tucson sounding (above from SPC) has a small amount of CAPE today - a more supportive sounding for storms wrt the last two mornings (note that there were isolated storms the last two days even with the very marginal soundings). The temperature this morning at 500 mb is a very cool -12C, which will help things along. Below is the WRF-GFS forecast of composite radar echoes at 4 pm MST this afternoon, with storms forecast for eastern Pima County. The 3 pm forecast sounding for Tucson indicates a small amount of CAPE above cloud bases at about 620 mb, where the temperature at cloud base is 0C. This is an excellent sounding for dry microbursts or downbursts. So we'll probably see an increase in gusty storms this afternoon.
Finally, Cat. 3 Hurricane Hilary continues on her westward course - usually a storm with her history would be headed out to sea. However, the models and NHC continue to forecast an abrupt turn to the north to occur by tomorrow morning. We will continue to watch how she behaves.
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