This morning PW and CAPE is considerably diminished relative to yesterday. There is still considerable instabilty at higher elevations and both the versions of the early WRF forecasts at Univ. of Arizona Atmo forecast some storm activity over eastern Pima County. Forecasts shown of composite radar valid at 1 pm MST this afternoon for WRF-GFS above and WRF-NAM below.
In the longer term, TS Ivo is forecast to move northward west of Baja, remaining a weak tropical storm and dissipating about half up the Baja coast. All models are predicting an influx of moist mT air because of the storm. However, since moisture alone does not directly determine small scale storms, the role of orography, heating, and local forcing will continue to be important through the weekend. The two early versions of the WRF (on the 5.4 km grid) predict very different rainfall patterns over the weekend for the Southwest - both forecasts show rainfall amounts forecast through 8 pm MST on Sunday evening. The WRF-GFS (above) forecasts the most significant rains up the Colorado River and across northwest Arizona. This is because the GFS model forecast from last evening brings a significant remnant of Ivo, at 500 mb, right up the Colorado River. In contrast the WRF-NAM (below) indicates a much different outcome, forecasting heaviest rains over eastern and northern Arizona. The large contrast results because the NAM forecasts Ivo to stay further west of Baja and not to move as far north. It will definitely be an interesting weekend and I suspect that the GFS version may prove closer to reality.
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