Sunday, May 5, 2013

Snow Melt…Up High There's A Long Way to Go

The pattern is definitely changing and spring is on the way to Fairbanks-land this week.

Here's the 500mb heights from the Sunday morning ECMWF (12Z 05 May 2013) run valid at 4am AKDT Friday 10 May: I've drawn in the ridge extending northwest from the big high over Washington. The green colors reflect higher than average clustering of the various ensemble members, which increases  confidence in this forecast. This would be a mild, but not overly warm, pattern for Interior Alaska. Given how high normal temperatures are now, this will get snow melt and break-up going full swing. The snow cover will go pretty quickly in town, helped out by 18 hours of sunshine. But at elevation it will take a while.

Here's a plot of daily snow depth here on Keystone Ridge for each spring the past 17 years. I've highlighted some of the notable years.
Obviously there is nothing like this year in any spring since 1997, and this is undoubtedly the greatest snow depth this late in the season here on the ridge since 1992. The current high value will decrease several inches simply due to compaction of the flurry snow that fell this past week. However, that still leaves a lot of snow that needs plenty of heat input to turn into water.

So what will the date of meltout* be this spring on Keystone Ridge? I'll go for 24 May, assuming a curve somewhere between the rapid decline in 2002 and the much slower rate in 2000, but note it's never a quasi-linear decline to zero: once the snow depth gets down to 10-12", it goes fast. 

*Meltout is defined here as the date when the snow depth fall to zero or trace. In practice, this means the date when the snow-free area in the vicinity of the weather station increases to greater than 50 percent coverage.


  1. Rick,

    Interesting data... the early April depths seem to fall in two clusters, around 12-16 inches and around 24-30 inches. I'm surprised how often the depth is less than 18 inches. I take it there is a significant minority of winters when the snow depth never exceeds about 20 inches; would this be true of both valley and elevated locations?

    As an aside, it seems the lack of thaw degree days is truly historic now (though soon to end, as you note). Assuming zero TDD today, we have three days with any TDD year-to-date, compared to a previous record low of 8 days through May 6 in 1945. The accumulation is 2.5 compared to the previous record low of 22.5 through May 6 (1948).


  2. Richard,

    Four out of 17 years here on the hill the max snow depth did not reach 20" at anytime during the winter, and that occurs slightly more frequently in the valley.

    Yes, the lack of thawing DD is remarkable, and the snow cover continues to show itself, e.g. the low of 16F at PAFA Monday AM.