A lot of exciting things can happen this time of year when the mid-latitude storm track interacts with monsoon moisture. The latest model runs really get my attention in this regard as they are putting out a good deal of precipitation in the southwest US.
The latest GFS shows the precipitation picking up in northern Arizona on Thursday. By 1200 UTC 10 OCT (0600 MDT Friday), precipitation is organized in a band that runs from SW to NE from northern Arizona and to western Colorado.
This precipitation region is to the north and northeast of Hurricane Priscilla, which is forecast to be off the coast of Baja California at that time. Such a precipitation feature is sometimes referred to as a Predecessor Rain Event, or PRE and occurs as enhanced vapor transport north of a hurricane experiences large-scale lift. Forecast soundings from Flagstaff at that time are saturated with precipitable water values of 25.4 mm (exactly 1 inch if you prefer US units), which is quite high for early October.
The precise track of Priscilla is still unclear, but the latest GFS has her decaying off the coast of Baja at 1200 UTC 11 Oct (0600 MDT Saturday) with a plume of integrated vapor transport exceeding 500 kg/m/s extending into northern Arizona.
That's impressively high IVT given the elevation of that region. The GFS also continues to produce heavy precipitation in the same banded region.
Total accumulated precipitation produced by the GFS exceeds 2 inches in a band that runs from just west of Flagstaff through SE UT and into SW CO. Precipitation maxima produced by the GFS along this band exceed 3 inches, and this is a model that cannot resolve fine-scale precipitation features like thunderstorms.
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| Source: Tropical Tidbits |
The ECMWF has a somewhat different idea about Priscilla's track and brings her through southeast Arizona. That smears the precipitation out more across the four-corners area and gives heavy precipitaiton to southeast Arizona and southwest New Mexico.
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| Source: Tropical Tidbits |
This has all the hallmarks of a late-monsoon, high-impact event for the southwest with heavy precipitation and flooding.
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