Thursday, November 18, 2021

Weekend Snow Prospects

The weekend approaches with guns blazing early this Thursday morning.  Below is a shot from Deer Valley illustrating the lack of natural snow cover at lower elevations and the ongoing artificial snowmaking efforts.

Temperatures, however, climbed overnight at upper elevations and today will not be as favorable as yesterday for snowmaking once the cold pools that remain at lower elevations burn off. Observations within 1 hour of 14:51 UTC (0751 MST) show temperatures near or above 32˚F in mid elevations, but still well below freezing at some lower elevation sites.  For example, it was 15˚F along SR-224 near the base of Park City Mountain Resort, but 31˚F at the top of Jupiter.  In Big Cottonwood Canyon it was 16˚F at the Cardiff Fork parking lot, but 33˚F on Reynolds Peak. 

It will help that the airmass is currently extremely dry.  The dewpoint on Mt. Baldy is about -30˚F, and this results in the wet-bulb temperature being much lower than the actual temperature.  The wet bulb temperature is the temperature you would have if you evaporated water into the air until it reached saturation.  It is a better indicator of snowmaking potential and quality than the air temperature.  It is possible to make snow at temperatures near or above 32˚F if the wet bulb temperature is below about 27˚F.  However, the temperature, humidity, and wet-bulb temperature will be rising today and this will make snowmaking difficult.  

Prospects for natural snow aren't zero, but a major storm for this weekend is unlikely.  Instead, it looks like we'll have a week system coming through Friday night and Saturday morning.  The time-height section for Salt Lake City summarizes the situation.  High humidity at upper levels will bring some high clouds at times today and tonight.  That upper-level moisture may bring a few dribs of precipitation tomorrow at upper elevations, but accumulations should be close to nil.  A weak trough and front move in late Friday night and early Saturday, bringing some periods of snow before the next ridge builds in.  

From about noon Friday to 11 AM Saturday, the GFS generates 0.28" of water and 3.5" of snow for Alta-Collins.  This is just above the middle of the distribution for the downscaled SREF ensemble, which has a mean water equivalent of about 0.22" of water equivalent and 3" of snow.  Some members produce scant amounts.  Four out of the 25 members produce > 5".   

Looks like a dust on crust event to me, with 2-4" most likely at Alta-Collins and perhaps a 20% chance that this is an overproducer that might do 5-8".  Could start as rain at mid elevations, but for the most part we should see snow at or above the base of Snowbird.  

If you are planning on touring at Alta, please see the information below.  Last day for uphill is Sunday.  


  1. The air mass at 700 mb and even a bit below that level was drier than I ever remember seeing. Soundings and surface obs yesterday and this morning showed dew point values around -50C (!) around 8,000 to 9,000 feet elevation. That made for humidity values of around 1% even with fairly cold temps. That seems pretty exceptional, I am trying to figure out the source and trajectory of such dry air.

    1. Suspect trop fold on back side of trough so air is of descended origin.

    2. That is the conclusion I came to as well, after looking back a few days. Its was a pretty dramatic trop fold I think.