Monday, December 3, 2012

Mt. Shasta Update

I thought it would be interesting to take a look at what happened on Mt. Shasta during the past few days given the forecast for prolific snows that came out on Thursday.

Here are some rainfall totals from the lowlands south of Mt. Shasta.  The graphs go back 5 days, but the totals cited in the text go back to 0000 PST 29 Nov.  One of the wettest sites in California was Brandy Creek (1300 ft), which is in the Whiskeytown National Recreation Area just to the west of Redding and roughly 80 km south-southwest of Mt. Shasta, where it appears 21.8 inches fell.

In the city of Mt. Shasta (3573 ft), just southwest of the mountain itself, 10.79 inches fell.

Stations on the mountain are limited, but there is a site at Sand Flat (6750 ft) on the southwest flank, which is indicated by the black dot northeast of the city of Mt. Shasta in the map below.

Sand Flat received 9.92 inches.

This elevation sat very near the freezing level for much of the event.  Through the grapevine, I received a report from Basil Newmerzhycky from Saturday afternoon on Mt. Shasta.  It was 34ºF at Bunny Flat (6950 ft) with moderate rain.  He observed mixed rain and snow up to an elevation of 7500 ft.  Most of the snow on the ground was from earlier storms.

Photo: Basil Newmerzhycky
What happened on the upper mountain remains unknown, but let's make some educated guesses.  Stations near Mt. Shasta observed about 10 inches of rain, including the site at 6750 ft.  It is interesting that the rainfall at Sand Flat was nearly the same as in the city of Mt. Shasta.  Perhaps there was a gauge error, but I wonder if the increase in precipitation with elevation was all that strong in this event at these altitudes (perhaps someone can dig through the data from the Sierra and see what it shows).  Let's give it the benefit of the doubt and assume that as much as 20 inches might have fallen.  For reasons we discussed in an earlier post, this would have happened at perhaps 8000-10000 ft.  These elevations were not far above the snow level.  In the Sierra, the snow that fell at these elevations had a water content of about 20%.  Thus, assuming that density, 10–20 inches of SWE gives us 50-100 inches of snow, a great event, but not close to a record breaker.

I'm sure some of you out there can poke some holes in these numbers.  It would also be really interesting to comb through the data for California in this event as it appears to be quite complex.

Addendum@633PM: I wrote this hastily before rushing to a meeting, so I wish add that extrapolating to upper elevations in this event is fraught with uncertainty, so the discussion above is simply to illustrate that it's highly unlikely that this event produced anything close to record setting snows on Mt. Shasta)


  1. Fun exercise Jim. Right you are, on stations and accumulations. No snotels near Shasta.

    Leavitt Lake, 9600 ft, 250 miles SE of Shasta went from 34" 11/28 to 82" 12/3, most on 11/30.,0/WTEQ::value,WTEQ::delta,SNWD::value,SNWD::delta

    Adin Mtn, 6200 ft, 80 miles E of Shasta had 2" of rain, no snow.

    Adin is a rain shadow of Shasta?

    20" precip on Shasta seems reasonable as an upper bound

  2. Yeah, that Leavitt Lake site suggests my 20% mean water content was generous. It may have been higher.

  3. If we have such a hard time predicting accurate snowfall now, how would we have predicted accurate snowfall during the previous record setting event?

  4. " Through the grapevine, I received a report from Basil Newmerzhycky from Saturday afternoon on Mt. Shasta. It was 34ºF at Bunny Flat (6950 ft) with moderate rain. He observed mixed rain and snow up to an elevation of 7500 ft. Most of the snow on the ground was from earlier storms."

    Amazing what happens when you "google" yourself. I never knew I had made it into "Wasatch Wx Weenies" years ago, while working for the USFS as a Fire Weather Meteorologist in Redding, CA. Yes, I was "In Search Of" the new record snowfall, and I remember the impressive Atmospheric Rivers setting up on the "Pineapple Express" out of Hawaii...taking aim on the Nrn Sierra and Srn Cascades. Would have been amazing if 700 mb temps would have been just 1 deg C lower.

    Now, having recently moved to Salt Lake City, I am in the uncomfortable position of NOT knowing the wx like the back of my hand. But learning is growth, and I have enjoyed reading these informative articles very much (and then skiing it, in order to validate results-lol).

    Thanks for maintaining such an excellent regional weather site. Wish I had this when I was going to school.

    Basil Newmerzhycky