Sounds Like A Broken Record

Warm, breezy winds out of the south, and high status clouds on deck... The PNW continues to get hammered with atmospheric rivers (AR's), with another decaying AR on tap for northern Utah today through the first half of this weekend (12/19-12/20). This feels like a broken record. Decaying AR's seem to be the new normal this season, and they unfortunately don't elicit the same weather excitement as full scale AR's. 

Sometimes, these "partial" AR's end up being more of a nuisance rather than anything satisfying. You get almost none of the benefits of an AR - large precipitation totals - and instead get all the disbenefits, including warm temperatures and high winds. In addition, because there is never a strong push of cold air, snow levels remain high, snow water ratios remain low, and snow pack in some areas has the opportunity to melt out. It's all a bit frustrating. 

ECMWF 00Z 12/19/2025 four-panel forecast 12/19-12/22/2025: (Top left to bottom right) MSLP/precip and 1000-500 mb thickness; 300 mb gph and winds; ; 500 mb gph, vorticity, and winds; 700 mb gph, RH, temp, and winds

The best opportunity for precipitation across the Wasatch Front looks to arrive Friday night through Saturday morning as the best dynamics and moisture arrives. Some scattered shower activity, mainly focused over the mountains, is possible through Saturday afternoon as conditions become more favorable for terrain driven upslope. Cottonwoods could get a little extra during that time. 

Total Snow (10:1 in) 12/19-12/20/2025 Left: ECMWF 12Z 12/19/2025; Right: GFS 12Z 12/19/2025

Snow and liquid accumulations don't look particularly impressive, with quite a bit of uncertainty and a relatively wide range in lower and higher end totals. For the Cottonwoods, there is the potential for anywhere between 4-10" of snow (~0.5 - 1" liquid) through the storm event (Friday-Saturday afternoon). Note, that most all of the snow accumulations will be above 7500-8000' and the snow that falls in the higher elevations will be wetter and dense. 

GFS 12Z 12/19/2025 Derived Alta, UT Snow Accumulation (in) 12/19-12/26/2025 (credit: UoU Atmo Sciences)

ECMWF ENS 00Z 12/19/2025 Total Snow (10:1 in)

The bombardment of AR's along the PNW and California coast looks to continue through the late weekend into the holiday week. This will provide an opportunity for a few additional shots of moisture to graze Utah Sunday through Tuesday of next week. However, once again, these will be 'warm' storms, with high snow levels and strong gusty winds at higher elevations. There are hints that this pattern will change somewhat going into Christmas Eve and Christmas and offer Utah a more robust storm, but too far out in forecasting fairy tale land to say for certain. In the meantime, we will have to make do...