An active weather period is coming over the next few days as several systems rumble through and eventually tap into moisture from a landfalling atmospheric river.
The NAM time-height section shows copious low-level moisture from later today all the way through the end of the forecast period at 0000 UTC Sunday (5 PM MST Saturday). During the period, several deeper systems rumble through, some associated with mid-level or surface fronts and associated troughs. Timing these systems is difficult and so it's best to say that we're going to be seeing periods of mountain snow that will add up to a considerable total by the end of the NAM forecast period on Saturday afternoon.
The GFS integrated water vapor transport forecast for 1800 UTC (11 am) Thursday shows a broad atmospheric river making landfall along the Pacific coast and penetrating inland across the northern Great Basin. We never get into full-blown atmospheric river conditions, but this is still a nice corridor of moisture transport into the region.
The image below shows our downscaled snowfall estimates from the NAM for the period. For the upper elevations of the Wasatch, amounts exceed 24 inches, with the northern Wasatch, which does well in patterns like this, over 36 inches. The NAM downscaled snowfall for Alta is 31 inches.
The SREF ensembles show precipitation beginning in earnest at Alta late tomorrow. Most members through 0000 UTC 15 Dec (5 PM Saturday) produce 1.2-2.2 inches of water and 18-34 inches of snow. There is one member that is much lower and two that go for more.
Numbers for the period are fairly similar at Snowbasin, but I suspect they will do better tomorrow (Thursday) and tomorrow evening when the pattern should favor environs to the north.
The bottom line is that a decent dumpage is coming. When each "wave" will come through is difficult to say, but totals should be significant through Saturday. I haven't bothered looking beyond that. A bird in hand is worth two in the bush.
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