Sunday, September 6, 2015

Winter Weather Dates

Here's a chart showing the temporal evolution of onset and ending dates for a few metrics of cold and snow conditions in Fairbanks.  Reader Eric suggested doing this for various seasonal metrics throughout the entire year, but I thought I'd start with just cold and snow conditions; there's enough to focus on here for now.

A couple of interesting features stand out:

- The first freeze has become considerably later over time (no August freeze since 1996), but the first measurable snowfall has become earlier, and the establishment of the permanent winter snow cover has also become slightly earlier.  Prior to about 1970 there was usually a lengthy period between the arrival of frost and the arrival of snow, but these days the transition is relatively compressed.  The slightly earlier arrival of snow cover is consistent with a long-term cooling trend in Fairbanks in autumn: most of October and early November have become colder since 1930 (in contrast to the rest of the year).

- Late winter and spring have become warmer over time, with fewer instances of late freezes and late 0°F occurrences, but it does not appear that the melt-out date has become earlier.  Consequently the continuously snow-covered season has become slightly longer.


  1. Thanks, Richard.

    The length of the growing season in the Interior has increased by a few weeks in the last few decades. This way of seeing the analysis suggests that most of the growth season lengthening is truly in the fall.

    I find it interesting that the difference between first freeze and first 0℉ has decreased by half. It's almost like nature holds off on cooling for as long as she can and then overreacts.

    I wonder if reanalysis will show us what has changed over time to create the conditions we see.

  2. So if the establishment of an early winter snow pack is trending for Interior Alaska, is the mean annual snowfall for Interior also increasing?

    1. Tracy, good question... that would make sense but I'm not sure. I'll put that on the list, I'm going to be traveling for the next week.