Gone with the Wind

Given that it is the U's spring break, I was fortunate to be able to get away for a ski tour yesterday.  It was a spectacular day, with fantastic snow and great skiing.  

The Wasatch looked amazing.  The snowpack is deep and the cover extensive.  It's the time of year when the north aspects are beginning to emerge from 24-hour shade and see the sun, making the views even more impressive.  A group of four clearly had a nice run down Stairs Gulch early yesterday.  

I spent most of the day reminiscing about what a great season it has been so far and what a remarkable run of cold snow and cold powder we have had.

As we discussed for several days, the storm track is shifting and we are moving to a warmer and windier pattern.  Indeed, except perhaps in a few highly wind-protected spots, yesterday's powder is now gone with the wind.  Gusts overnight reached over 90 miles per hour at ridge-top locations.  Temperatures have climbed to near freezing at 7500 feet already.  There may still be some good mid-elevation powder on north aspects in a few places, but the damage is being done from the top down and the bottom up.  

On the plus side, there is a storm brewing for today and tonight.  The two key ingredients are strong vapor transport associated with an inland penetrating atmospheric river and a frontal pushing in from the west.  At 0000 UTC 11 March (5 PM MST Friday), the atmospheric river is draped over northern Utah just ahead of the front.  

By 0600 UTC 11 March (11 PM Friday) the front is just south of the Cottonwoods.  

And by tomorrow morning it is through and we are post-frontal, although this is not a situation we would expect the Alta post-frontal magic to kick in as it's simply not unstable enough to generate orographic or lake-effect snow showers tomorrow morning.  

Looking at our GFS and HRRR derived forecasts provides a decent look at the range of possibilities between now and tomorrow morning.  The GFS  cals for mild conditions today and through this evening with Mt. Baldy (11,000 ft) temperatures in the low 20s and the wet-bulb zero level near or just above 8000', which would indicate a snow level near or just above 7000 feet.  Snow-to-liquid ratios are between 5 and 9 during this period, meaning high-density snow at upper elevations with periods of light precipitation.  After this evening, temperatures and the wet-bulb zero drop and snow ratios increase.  For Alta-Collins, the GFS generates 0.89" of water and 7.3" of snow through tomorrow morning.  

The HRRR is warmer and wetter.  It pushes temperatures on Mt. Baldy to 25˚F this afternoon and the wet-bulb zero level to 9000 feet, which would result in a snow level that flirts with the base of Snowbird and Alta.  It is also wetter today and with the frontal passage, generating 1.77 inches of water and 12.3" of snow for Alta-Collins through tomorrow morning.  

My synopsis is that these two model forecasts probably represent a reasonable range for the forecast through tomorrow morning, so my expectation is for 0.8 to 1.8" of water and 7-14" of snow at Alta-Collins by 8 am tomorrow.  Then the storm will be over.  This will be high-density snow and ski quality will probably depend on how much snow comes in the later stages of the cold-frontal passage when snow-to-liquid ratios are higher.  More snow then would at least give a right-side up profile.  

At lower elevations, expect rain today and this evening.  Some snow is possible on the benches or even on the valley floor late in the frontal passage tonight, but it won't add up to much. 

As most of you have probably heard, two skiers were buried in an avalanche yesterday in the Uintas, with one killed.  A preliminary report is available here.  I share my deepest condolences with their friends and family.