Model forecasts have been waffling wrt how much moisture the weekend system will have available as it moves across northern Mexico on Sunday. The latest NWS NAM forecasts are drier when compared to yesterday morning's runs. So, a look here at what the 06 UTC WRF-NAM runs from Atmo are currently forecasting for Sunday.
Closed low at 500 mb has been digging south, as per the larger-scale forecasts for a number of days. The 11 UTC water vapor image (above) shows the upper-tropospheric circulation to be centered west of the Californina/Mexico border at about 130 W and 30 N this morning. The WRF-NAM forecast for 500 mb (below, on 5.4 km grid and valid at noon MST on Sunday the 12th) indicates that the low is still a closed circulation that is centered south of Nogales. Coldest 500 mb temperatures are also to our south over northern Mexico.
Above is the WRF forecast of composite radar echoes, also valid at noon on Sunday. Widespread echoes over southeastern Arizona are fairly light. The forecast sounding for Tucson (below, valid at 5:00 pm MST on Sunday) indicates no CAPE at lower elevations, along with a fairly dry sub-cloud layer. Not a great situation for a substantial rain event. The WRF forecast of total precipitation through 11:00 pm on Sunday (at the bottom) currently keeps decent rainfall amounts off to the east and south of Tucson metro area. However, this event is still a couple of days away and we can hope that features come together better than the current WRF forecasts indicate.
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