Real Winter

The GFS 500-mb forecast for 1800 UTC 19 January (1100 MST Sunday) is one that should put a smile on the face of anyone who misses "real winter."  An incredibly deep and broad trough, centered near Hudson Bay, covers most of North America.  

As a result, the 5-day average forecast surface temperature anomalies, or the departure from average, centered on that period is negative (or below average) across much of the United States and Canada, with a bull's-eye near the border of North Dakota and Saskatchewan.  

Source: tropicaltidbits.com

It's nice to know that Mother Nature can bring it still from time to time.  

It will be getting cold in Utah, but really we are going to miss out on the coldest of the air thanks to protection from the Continental Divide.  Forecasts from the National Weather Service National Blend of Models for KSLC show maximum temperatures dropping from 39-43F today to the low 30s tomorrow and then possibly into the 27-32F range on Monday.  Minimums eventually get down to the low to mid teens on Monday night.  

Winter, but not brutally so.  For perspective, the average high/low for this time of year is 39/24 (based on 1991-2020 observations).  

There are a couple of short-wave troughs that drop down the back side of the long-wave trough during this period, but they are pretty moisture starved.  Probably the best shot for mountain snow is from late today through tomorrow morning.  The GFS forecast valid 1500 UTC 18 January (0800 MST Saturday) shows the trough right over northern Utah with some precipitation over the mountains.  

This is a crap shoot situation given the limited moisture.  Much will depend on instability, lake influences, and, for Little Cottonwood Canyon which might have the best chance of something, maybe some Alta magic.  There isn't much model agreement for snowfall through noon tomorrow.  The 12Z HRRR is pretty much a nothing burger (.06" water with 1" of snow).  The GFS is a bit more enthused (0.35" water with 6" of snow).  Most of the Utah Snow Ensemble members are between .22 and .47" of water and 3.5-8" of snow.  

You may be able to tell from those numbers that what we get is likely to be of the low-density variety where it isn't trashed by the wind.  Temperatures tomorrow morning are going to be frigid, with our forecast for Mt. Baldy (11,000 ft) of -4F and Alta-Collins (9600 ft) of 2F.  

Keep your boots and toes warm.