A substantial trough will impact the Southwest beginning on Saturday and extending through the next five days or so - thus, an impending event that will be much different than the quick-hitting short wave of Tuesday the 24th. Above is the ECMWF four-panel forecast valid at 96-hours (5:00 pm MST on Sunday). Note that the global models are forecasting an influx of moisture from low-latitudes into this system. The GFS ensemble average and spaghetti charts for 500 mb valid at the same time are shown below.
The NWS Weather Prediction Center (WPC) makes national guidance forecasts of Quantitative Precipitation (QPF), and since this event is still quite a way in the future I'll show a couple WPC products. Above is their QPF forecast for days 4 and 5 (i.e., for the period 12 UTC Sunday through 12 UTC Tuesday). The WPC forecasts a very impressive event from San Diego, across Arizona, to the Colorado Rockies. Currently their forecasted maximum amount over Arizona is above 3 inches on the Rim near Payson.
The WPC also issues probabilistic forecasts for a wide range of precipitation amounts - these are called their PQPF forecasts. These forecasts are valid (understandably) for shorter, near-term periods. I've shown below their forecast of probabilities for at least 0.10" for the six-hour period ending at 5:00 am MST on Sunday morning - i.e., before the event really impacts most of southern Arizona. As the event approaches I'll show some more of these interesting products.
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