Friday, April 18, 2014

Sudden Onset of Thawing

After a slightly delayed start, the thawing season has suddenly gotten under way in the interior, and in only a few days the snow depth at Fairbanks airport has dropped in half (from 20" on Sunday to 10" today).  The year-to-date accumulation of thawing degree days, defined as the excess of the daily mean temperature above 32 °F, will be above normal in Fairbanks after today.  The chart below shows the annual thawing degree day accumulation through April 17; I think there is a strong connection here between earlier onset of thawing and El Nino conditions in the preceding months.

It is of some interest to note that this year looks like being one of the unusual ones in which freezing conditions in Fairbanks (mean daily temperature below 32 °F) give way to thawing conditions (mean daily temperature above 32 °F), with no period of back and forth.  This occurs in about 10 percent of years and last happened in 2007.  For comparison, a sudden transition in the opposite direction in the autumn happens in about 15 percent of years - a little more often, because the autumn cooling is more rapid than the spring warming.


  1. El Nino comments:

    Yes conditions in Fairbanks are warming and melting. Enough of winter. It's time for summer so we can prepare for winter.

    Smashed my first mosquito last eve working on the roof clearing the mess from last November's windstorm and surveying the damage from the fallen trees.

    Waterfowl are flying about as well.


  2. Since the first 50°F day on April 13th, it has been 50°F+ every day since. I wonder if that has ever happened before?

    1. Brian,

      Remarkably, the answer is yes: in 1964... of course! Besides the record cold you mentioned, that year had the latest Ice Classic breakup prior to last year. The first 50F day in 1964 was May 24, by far the latest on record; but within a week it was 81F.

      Based on the long-term history, the chance of not having another sub-50F day this spring in Fairbanks is rather small, but it certainly could happen.

    2. Maybe this has been covered - but how many years on record have had overly delayed springs then sudden death heat like 1964 and 2013? Did those years all have similar regional climate patterns? I wonder if we can predict them - I didn't like last year.

    3. Eric,

      1964 was really extreme in this regard - more so than 2013. 2002 saw a rapid warm-up with few 50+ days through May 10, but then it was 80F on the 20th. A quick look suggests a negative PDO phase may be a common factor, but I would need to find more years to do a proper investigation.