Thursday, November 29, 2012

Is a US Snowfall Record in Jeopardy?

From the Weather Channel today, an article entitled "Mt. Shasta: Is U.S. Snowstorm Record in Jeopardy?


To quote the article, "The Thursday morning National Weather Service summit forecast for Shasta predicted an incredible 33 to 39 inches of snow -- just for Thursday alone...Add up the high end of the numbers and you get a forecast maximum of 218 inches of snow in four days!"

Unfortunately, this is an example of extrapolation and sensationalism run amok.  The world record single snowstorm accumulation of 189 inches was set from Feb 13-19, 1959 at Mount Shasta ski bowl. The ski bowl is going to get a pounding over the next few days, but some of the precipitation is going to fall as rain.  Snow levels are quite high in this storm.  Here's what the base looked like at noon today.


What about higher up on the mountain?  Well, the 218 inch figure noted above is for the summit.  Surely it will snow a ton there?  

Unfortunately, precipitation can't always increase with elevation, as I think was assumed for these forecast numbers, especially on a big mountain like Shasta.  Typically on such huge mountains, the heaviest precipitation falls at mid elevations, near 8000-9000 ft.  There are many reasons for this, but one that is evident at times over the next few days is that storms don't always extend to the summit.  For example, during some periods during the next few days, the storm is capped at about 700 mb, or 10,000 feet.


It is also illustrative to consider the circumstances during the 1959 storm.  During that event, there were prolific snows not only on the mountain, but also in the lower elevations.  Mt. Shasta City, at ~3600 ft. had a reported 33 inches of snow during the first day of the storm.  Unlike the current storm, that was a cold storm, and I suspect the snow that fell at the Mt. Shasta snow bowl was somewhat drier than average.  This helps to yield larger accumulations.

So, the answer to the Weather Channels question is no.  This will be an impressive storm at elevations perhaps in the 8000-10000 ft band on Mt. Shasta, but records will not fall.  Maybe one of you can go up and measure for me to confirm this.

9 comments:

  1. The history of lift- service downhill skiing on Mt. Shasta began in 1959 with the creation of the old Mt. Shasta ski bowl, located at the end of Everitt Memorial Highway.
    The old Ski Bowl was situated above the tree line and was routinely plagued with whiteouts, avalanches and road closures. In 1978, the Ski Bowl was struck by a huge avalanche that destroyed the main chair lift.
    From 1978 to 1985 there was no downhill skiing on Mt. Shasta. In 1985, a group of local businessmen formed Wintun Development Company with the express purpose of re- establishing skiing on Mt. Shasta.
    In the summer of 1985 construction began. The Mt. Shasta Ski Park opened December 14, 1985. The current ski bowl as pictured above is at 5500' and is a gross misconception of what is really happening up higher on the mountain

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  2. David-Much thanks for the clarification and the great summary of the history of the ski bowl and ski park.

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  3. NWS forecast probably uses some type of interpolation method that increases precip with elevation. Could be a bit overdone up top.

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    1. When you are attempting to calculate estimates of values outside of your observational window (no bounding values) you are extrapolating. This is very different than interpolating, which is calculating an estimate of a bounded (by observations) value. For example, if one wanted to calculate the amount of snow at 9k on Shasta and observations existed only at 6k and 10k (and preferably others), you would interpolate to obtain the 9k snowfall. However, for 12k, you would be extrapolating and be at risk of a variety of factors that could skew your results dramatically. When snow and complex terrain are involved, even interpolation can give you bogus values. Expect 2 ft. Observe bare ground. Scouring! Expect 2 in. Observe 4 ft. Drifting! Spatial variability at its finest!

      Either way, some 7000 vertical foot December ski runs are now possible!

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  4. I haven't been able to find out how much snow actually fell. Did anyone end up measuring this?

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    1. See http://wasatchweatherweenies.blogspot.com/2012/12/mt-shasta-update.html

      No direct measurements that I'm aware of.

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    2. The link indicates that we don't know how much fell. I'm curious how we could have measured the previous record setting event. I don't know how these things are measured. Thanks for linking.

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    3. Meteorological records are typically based on where measurements are taken rather then estimates from interpolation or extrapolation. The Mt. Shasta Ski Bowl record is the largest single storm accumulation *ever measured* (http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=98 suggests that there might be a contender from the 1800s). Web reports suggest that the ski bowl observing site was at an elevation of about 7900 ft. As noted by commenters above, the ski bowl was closed and the newer snow park is lower on the mountain. Thus, we no longer have an observation at 7900 ft. Pity...

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