Winter's last gasp earlier this week had a sharp bite to it in the interior and north, with overnight temperatures dropping well below zero at many locations. Here are a few notable readings from Wednesday morning:
-24°F at the Birch Creek HADS
-16°F at the Livengood RAWS
-17°F in Bettles and Coldfoot
-27°F at the Dahl Creek HADS
-20°F at the CRN site to the east of Kaltag
It's pretty late for this kind of cold. In Bettles, for instance, only one year (since 1951) has recorded a temperature below -15°F after April 20, and that was only marginally later in the month (April 22-25, 1966).
Accumulating snowfall is likely finished in Fairbanks, so the tentative total for the season fell just short of 100". It was the snowiest winter since the triple-crown big snow winters of 1990-91 through 1992-93.
In view of the Fairbanks snow onslaught in February, and similar heavy snows in Anchorage and Juneau, I thought it would be worth looking at the contribution of the snowiest days and months to seasonal snow totals at all three sites. For example, the top 10 snowiest days of each winter generally contribute about half of a winter's total snow accumulation in Fairbanks; but has this changed over time? Fairbanks typically "nickels and dimes" its way to a substantial snowpack, but is this more true of recent years or of an earlier climate?
The answer is there hasn't been any significant change over the decades. Click on the following chart to enlarge; it shows the seasonal snow totals in light blue, the contribution of each winter's 10 snowiest days in dark blue, and the ratio of the two totals in red.
There are slight increasing trends in snow totals in Fairbanks, and there's a hint of a decreasing trend in the "top-10-days to seasonal total" ratio, implying that heavy snow days used to contribute a bit more of the total snowfall - but the trends are nowhere near statistical significance.
Another perspective on the question is to look at the snowiest 30-day period each winter and calculate its contribution to the seasonal snow total. Again, there's a slight decrease in the snowfall fraction attributable to the snowiest month, but it's not a significant change.
Anchorage also exhibits slight - but not significant - upward trends in snowfall, both in terms of seasonal totals and each component of the segmentation. The snow fraction derived from top-10 days and the snowiest month haven't changed significantly over the 72 years of data in Anchorage.
A more striking result is found in Juneau, where both fractions have increased very significantly in the 82-year climate history. The snow totals themselves haven't changed significantly, but there's clearly a substantial increase in the concentration of snowfall in the heaviest episodes, starting in 1976-77.
It seems to me that the change in Juneau must reflect the increase in winter average temperatures that also developed in the late 1970s, when the PDO phase turned positive. In Juneau's mild climate, warmer winters have more days with rain rather than snow, and therefore the snow events make up a larger fraction of the winter's overall snowfall. (To understand this, consider the extreme of a much warmer climate where snow is rare; 100% of the snow will occur in the top-10 snowiest days each winter.)
The surprise, perhaps, is that Juneau hasn't seen a more significant decline in total snowfall; there is a negative slope, but it's not close to statistical significance. However, it seems possible that the inter-annual variance is increasing; many recent years have had low snow, but there have been very snowy winters too, culminating in this winter's all-time record.
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