Friday, March 16, 2018

Interior Snow Pack

I'm up in Fairbanks this week, getting a taste of late winter conditions - although warmer and snowier than normal for the time of year.  Today I took a trip up to the Chena River State Recreation Area to get a first-hand look at the snow pack in the hills, and I can state unambiguously that there is a lot of snow on the ground.  The photo below was taken at about 800' elevation.



I wrote about the above-normal Chena Basin snowpack back in January, and the chart below updates that analysis through today.  Remarkably, the average of 5 sites that are reporting snow water equivalent is close to double the 1981-2010 median for this date, and it's close to a record.  The only year with more snow on the ground at this date was 1993 - no other year comes close in the SNOTEL data for these 5 sites (1981-present).  The winter of 1992-1993 brought 139" of snow to Fairbanks (3rd greatest on record), and March 1993 was the last time the measured snow depth reached 3 feet at the airport.  For comparison, Fairbanks has had nearly 80" of snow so far this winter, with a peak snow depth of 32".



It's worth noting too that the snow water equivalent (SWE) is at or very close to record levels for the time of year at 3 of these 5 SNOTEL sites.  The SWE of 9.7" at Mt. Ryan (2800') is not far off the all-time record of 10.5" (April 1993), and the remarkable 14.8" that's currently being reported from Munson Ridge (3100') was exceeded only in 1991 and 1993.

The map below provides a broader look at snow pack in regions where data are available.  Significant shortfalls are evident in south-central and southeast Alaska, and this is related to La Niña, which reduces the number of storms in the Gulf of Alaska.  On the other hand, snowfall has been above normal in the interior and at least as far north as the Brooks Range; the Atigun Pass SNOTEL is currently reporting a snow depth of 57", which is a new record for March and ties the all-time record for the site (1983-present).


3 comments:

  1. in late winter Fairbanks it seems we often have periods of very brief, very heavy, snow squalls. They have very sharp boundaries and I often see the abrupt edge of precipitation approach from a quarter mile away. The clouds that produce these showers are similarly broken with blue sky visible. This last week in Fairbanks is a good example. How do these form? They are discrete like June thunderstorms but I can’t imagine there is much thermal convection. They don’t seem part of a larger system. Whatever the cause, they always seem to be the last snow of winter in Fairbanks.
    Bill Witte

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  2. Bill, great question. The heavy snow showers on Monday afternoon were exactly as you describe. It may seem unlikely but they are convective, i.e. caused by vertical temperature gradients. At this time of year there is a fair amount of power in the sun to produce surface warming, but the temperature aloft can be very cold, and with the right flow configuration it's not difficult to get vertical instability.

    The process is essentially the same as for summer thunderstorms but with much less moisture available owing to the lower temperatures.

    I'll see if I can put up a post on the topic, as it's very interesting. Thanks!

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