And Another Storm is Coming

Forecasts look good for another storm Saturday night and Sunday.  The latest GFS forecasts a healthy trough to be over Utah at 1800 UTC (11 AM MST) Sunday with precipitation across much of the state.  

The corresponding GFS time-height section for Salt Lake City shows a relatively dry low-level airmass this morning, with moisture moving ain at low levels after 0000 UTC (5 PM this afternoon).  Through about 1500 UTC, moist SSE to SSW flow prevails near and below crest level.  This is a good setup for precipitation not only in the Cottonwoods, but also on the Wasatch Back.  

The GFS forecasts the trough to move through between 1500 UTC and 1800 UTC (8 AM and 11 AM) Sunday, after which moist northwesterly flow prevails.  If you wanted to complain about this storm (and you probably shouldn't), the post-frontal northwesterly flow doesn't look especially unstable, although I'm not going to lose any sleep over that because this still loops like a decent storm. 

Let's look at some numbers.  The GFS is going for a Goldilocks storm with 0.95" of water and 13" of snow at Alta through Sunday evening.  Snow-to-liquid ratios increase with time, favoring a right-side up snowfall.  Wet bulb zero levels max out tonight at about 6200 feet, so expect snow levels to start out near or just above the benches and lower with time.  It's a tough call whether or not they will reach the valley floor (they get close) so if you need to drive Sunday morning or Sunday, suggest keeping an eye on the forecast.  

As has been the case the last few storms, the HRRR is a bit warmer, with the wet bulb zero perhaps 500 ft higher, and wetter, producing 1.75" of water and 20" of snow for Alta by Sunday evening.  That's more at the upper-end of the Goldilocks range.  

It seems like 0.9 to 1.8" of water and 10-20" of snow is a decent bet for accumulations through Sunday evening.  Sunday looks like a storm-skiing day with free refills at the resorts with the GFS and HRRR forecasting the trough moving through upper Little Cottonwood from 11 AM to 2 PM (note how the flow in the center left plots above shift from southerly to WNW.  Late-day red-snake potential looks high.