Tuesday, October 29, 2013

Better than Expected...I Think

This time of year when ski area and snow safety operations are still a few weeks away, we rely on a very small number of automated stations to provide us with information on snowfall in the mountains.  In addition, automated snow-depth gauges tend to be a bit sketchier when the snow depth is low.  Therefore, there's more uncertainty than usual in determining how much snow fell last night.

The Snowbird SNOTEL came in with about 1.3" of snow-water equivalent after temperatures dropped to near 32ºF.  The automated snow depth sensor was fluctuating around an inch prior to the storm, and currently measures 13 inches after a peak at 14 inches.  

Alta–Collins recorded a bit less.  The total snow depth increased from 12–15 inches prior to the storm (pick your favorite, note that this depth sensor read 6 inches when the ground was bare a couple of weeks ago, so deduct 6 for a snow depth estimate) to 24 inches at last observation.  The interval stake recorded 10".  

So, let's call it something like 10–12 inches in upper Little Cottonwood.  If you want a better estimate, you'll just need to go up and measure it yourself!

Much of that snow fell late yesterday and last night.  The storm structure and dynamics have since changed and an interesting aspect of the storm this morning is the persistence of echoes along the Alpine ridge between Little Cottonwood and American Fork Canyon.  

In particular, note that the radar echoes are stronger and more persistent from about Lone Peak to the Pfiefferhorn and weaker and less persistent in upper Little Cottonwood including Snowbird and Alta.  We sometimes see this in southwesterly flow when shallow orographic clouds are generated by forced ascent from the Utah Valley over the Alpine Ridge.  The photo below, which looks southward toward Lone Peak from the University of Utah, shows some of the shallow orographic clouds being generated by the southwesterly flow over Lone Peak.  

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