Tuesday, December 24, 2019

Prospects for a White Christmas

Although the Eve of Christmas Eve brought some light rain showers to the Salt Lake Valley, snowfall at Alta yesterday, overnight, and this morning has added up to a surprisingly healthy 9 inches.  If you aren't used to interpreting the "Snow Interval" column below, it's an automated measurement of snow depth on a wooden board that gets wiped from time to time.  You can see below how 2 inches accumulated through 16:00 yesterday afternoon (time increases upward), then the board was wiped, another 4" fell through 4 AM when the board was wiped again, and then another 3 inches fell through 8:00 this morning. 

Source: MesoWest
What will happen tonight as Santa delivers his gifts and tomorrow when Johnny and Jane want to play with their new sleds?  I'm not going to lie to you.  I don't have a good idea and I'm glad I don't have to tell Santa that.  The pattern is messy with a bunch of disorganized areas of precipitation in southwesterly flow initially and a weak front moving through overnight.  There's not much that one can "count on" in a pattern like this, so much is going to depend on luck. 

Downscaled NAM accumulations from 5 PM MST (0000 UTC) this afternoon through 5 PM Christmas Day amount to zilch right on the valley floor, and 4-8 inches in the upper elevations of the central Wasatch. 

A look at the SREF plume for Alta shows this morning's snow, a break today, and then some additional snow tonight and/or tomorrow depending on the member.  Deducting this morning's snow, the average total through 5 PM Christmas Day (26/00Z) is about 6-7 inches.  The range for all but two very excited ensemble members is about 1-9 inches.  

At the Salt Lake City Airport, all but three members generate less than in inch. 

While it won't take a Christmas miracle for there to be an inch or more of new snow on the valley floor by Christmas afternoon, the odds are low.  The east bench odds are a bit better, but still most members are under an inch at the University of Utah.  

However, the forecasts above are based on science and with a little Christmas magic, perhaps the low probability outcomes will verify.  Really, that wouldn't be magic.  Statistics says it could be so.


  1. I live in Daybreak, for some reason Daybreak consistently gets 2-4 more inches of snow than the surrounding towns and Salt Lake, I think this peculiar, though it could be due to being on the west bench. I would think so, if we did not also consistently get 1-2 more inches than Herriman. The only thing I can think of, is lake effect snow??? Yet I am extremely skeptical as Daybreak Lake is pathetically small. What are your thoughts?

    1. I've been curious to see if this is an effect of the southwesterly storms.