Friday, October 16, 2015

Snow Depth Graphic, Yukon Ice

Returning to the subject of the unusual September snowfall in Fairbanks this year, I created a different kind of graphic to illustrate the fate of all early autumn snowfall events in Fairbanks since 1930.  The chart below plots all non-zero snow depth observations from September 1 through October 15 in Fairbanks, with snow depth on the vertical axis and date on the horizontal axis.  Red markers indicate snow that subsequently melted out before the arrival of the permanent snowpack, and blue markers denote snow that stayed.  The "x" markers show the observations from 1992 and 2015.


A few features stand out on the chart.  First, this year's snowfall, despite being very unusual, was clearly much less anomalous than the 1992 event, which produced 10" on September 15.  Second, there have been other instances when 5-8" of snow in the first week of October melted out, so in retrospect it isn't too surprising that 11" on September 29 couldn't survive.  The 1992 event was accompanied by incredible cold that was arguably even more unusual than the snow.  Excluding 1992, there are hardly any blue markers prior to October 5, so it's very rare to see the permanent snowpack before that date.

The chart also illustrates that a snow depth above 4" after October 10 is very likely to survive; it's tough to melt snow in mid-October, even with sunshine and above-normal temperatures.  The downtown Fairbanks webcam shows traces of snow on the roof of the Yukon Quest HQ today, 10 days after the airport lost its snowpack, and after some unusually warm conditions.  The Goldstream Creek COOP near Fairbanks was still reporting 4" of snow on the ground as of yesterday morning.


On another note, there is now plenty of ice on the Yukon River at Tanana, as a result of some cold nights, particularly farther upstream; the Beaver RAWS was down to 2°F on Tuesday.  Here's a loop of the FAA webcam view in Tanana for most of the day today.

video

Update October 17: at least part of the Yukon is frozen over today at Beaver.


7 comments:

  1. Given the current weather pattern what are the odds of a snowfallless October at the Fairbanks airport?

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    1. Well, it appears there's a chance of a bit of snow on Monday, but whether it's cold enough to stick is another question. I wouldn't rule it out even in this pattern; Tanana got some accumulating snow last night.

      If it doesn't snow on Monday, then it looks dry through the end of the week, leaving only about a week left in the month. However, in the period Oct 24-31, measurable snow has fallen in 80 of 85 years, so there's a good chance it will happen by the close of the month. October has never been snowless in Fairbanks (2013 was the closest, with 0.7 inches).

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  2. Thanks Richard! This winter will be interesting to see if the persistent ridging that occurred almost continually as of late returns this winter. Will the west be as analmosly warm as last year or just above average....
    I love interior winters but my heating bill likes the warmer weather better.

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  3. Richard, looking through the old Coop forms, the observer(s) noted the first run of ice in the Yukon for 22 of the 45 years between 1916 and 1960. The average date for the first flow of ice was October 18th. I'll do an analysis of accumulated freezing degree days and see what the relationship looks like.

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    1. Well that is very interesting Brian. The average date is a bit later than I would have expected. Look forward to your analysis.

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    2. The dates I provided were for the Yukon River at Eagle. Sorry for the confusion.

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