Friday, February 5, 2016

Surprise Delivery

After yesterday's bummer of a trough passage, which produced all of one inch at Alta-Collins, I confess that I was in quite a pessimistic mood when I went to bed last night.  Thus, it was a pleasant surprise to wake up to a fresh coat of some of Mother Nature's finest dendrites.

The real surprise, however, was in the mountains.  The Little Cottonwood snowmaking machine was really cranking last night with Alta-Collins picking up 11 inches of cold smoke.  That appears to be quite a bit more than fell elsewhere in the Wasatch, as well as that predicted by the models and by operational forecasts.  The National Weather Service Little Cottonwood forecast issued yesterday afternoon called for a 20% chance of a trace and an 80% chance of 1-3".

Source: NWS
And just to show I'm not picking on them, I last did a blog post on Wednesday and while it examined the high-amplitude ridge that will be building over us the next few days, I did mention that I expected 2-4" from yesterday's trough passage.  Some of that I expected to fall during the day yesterday.  If I had produced a forecast yesterday, it probably would have been no better than the NWS forecast and more likely worse.  Other ski weather forecast sites also crashed and burned.  I'd be drinking, but I've consumed my stock of Forecaster's Friend following previous forecast busts.

We still have some work to do, especially regarding what I like to call the "post-frontal crap shoot." It is during these periods of northwesterly flow, when snowfall is produced by shallow convective clouds that are highly sensitive to the depth and strength of instability and moisture, as well as with flow interaction with the mountains and sometimes the lake, that we struggle the most.  Last night provides a good example. 


  1. Did it hit "Steenburgh Winter" today? Alta's website shows the base depth at 100 inches, but the Collins hourly only shows a peak of 98 inches. Regardless, it's already settling fast....

    1. Nope. It needs to be 100" at Alta-Collins. Yeah, I know, semantics, but the byline of this blog is "Mountain Meteorology and Snow Snobbery" and I need to keep up appearances.

  2. On Feb 1st and Feb 2nd UtahSkiWeather mentioned the possibility of up to 12 inches in LCC! Then we trended down a little, I'm not saying they were great forecasts but I wouldn't say crashed and burned either!

  3. I was really surprised to see that too.... the orographics must have been pretty shallow, considering that the low levels were stable and there was also strong stability above 650 mb due to a building upper-level ridge. It must all have happened in about the 650 to 750 mb layer based on the sounding. Also, why the very high snow/water ratios? It looks like the snow producing layer was in the -5 to -15 C temp range which is not particularly cold or anything.