Weather for the start of the Labor Day weekend today (Friday) looks pretty good. The large-scale pattern hasn't really changed dramatically for some time. There's a trough centered over the Pacific Northwest coast and a ridge over the central US. These features have been around for some time, shifting in strength and position. Right now, the southwesterly to southerly flow between these features is relatively dry, so shower and thunderstorm activity is suppressed or limited. Today should be quite nice across most of Utah other than some gusty winds, as indicated by the ECMWF HRES forecast for 0000 UTC 5 September (1800 MDT Friday).
However, lurking in that forecast is Hurricane Marie off the coast of Baja (Hurricane Karina is also visible in the plot farther to the west). Marie is expected to move northwestward over the next few days, and therein likes the forecast problem. Although Marie will weaken, her moisture is going to move into the southwesterly flow ahead of the upper level trough, leading to another surge of moisture into Utah. The ECMWF HRES forecast for 2100 UTC 6 September (1500 MDT Sunday) shows this well. Marie (yellow L) has drifted ever so slightly northwestward and with high relative humidity air and strong vapor transport extending to her northeast and into Utah (red arrow).
Although we developed the Utah Snow Ensemble for powder, it does include downscale precipitation forecasts. Below is the forecast of 6-h accumulated precipitation for Sunday afternoon [1800 UTC 6 Sep to 0000 UTC 7 Sep (1200-1800 MDT Sunday)]. The upper left is the ECMWF HRES showing a band of precipitation extending across central Utah from St. George to the Uintas (upper left), although there is also some precipitation in other areas. The ensemble mean also keys in on that area (upper right), again with some members producing precipitation in other areas.
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