Saturday, April 20, 2013

Fairbanks Snow Melt…Getting There…But Not Quite Yet

Milder weather has come to Fairbanks-land, and so the long process of snow melt and river ice break-up will, after a couple week delay, get underway. Here was the view on Smith Lake, at the west end of the University of Alaska Fairbanks campus on Thursday afternoon (April 18th), when trail conditions were still "perfect".
Courtesy of Ed Plumb
Temperatures finally cracked freezing early Friday afternoon and we now look to be into the thaw-freeze diurnal cycle, with mild days and clear cool nights. This will allow for slow ripening the snow pack, a necessary step in before substantial runoff can commence. One measure of how this process is progressing are thaw degree days, which are simply the sum of daily mean temperatures above freezing. Below is a plot of cumulative thaw degrees at Fairbanks through April 20th for each of the last 108 years, expressed as the difference from the mean.

Through Saturday, Fairbanks has cumulative total of zero thaw degree days since March 1, 47 below the mean . How unusual is this? Well, it's not unprecedented: 1960 and 1954 also had zero thaw degree days through April 20th. However, we don't want to get too hung up on "zero". After all, "one" is not very much different than "zero. Next is a histogram of the above data:

So having accumulated very few thaw degree days at this point is not unusual;  11 percent of springs have five or less through April 20th. So, while it is unusual not to have any significant snow melt thus far, it is well within the range of past experience. If Saturday's numerical weather models are vaguely correct, we'll start to accumulate those thaw degree days pretty quickly next week and with it snow pack ripening.


  1. Rick,

    Thanks, great analysis! Thaw degree days are new to me. Looks like today may perhaps be the first day with a TDD in Fairbanks, if so it will tie the 1960 record for latest occurrence of a daily average above freezing.

    It might be interesting to repeat the analysis in a week or so, as the medium-range forecast looks pretty chilly! In 1960 it was a heck of a warm-up...


    1. The cold nights thus have squashed the any TDD even with the warm afternoons. Looks like we might have a new the 4pm max temp is 48F and clouds have moved in and west wind have picked up.