More Snow in Anchorage

Anchorage is off to a remarkably snowy start to winter, with 22" reported since the beginning of the week, and a snow depth of 19" on yesterday's climate observation.  Only a handful of years have seen greater snow accumulation by this date, and none has reached a snow depth of 19" this early.  With consistent climate data back to 1953 (at the international airport), the previous earliest date with 19" or more on the ground was... last year, November 10.  Prior to that, the earliest was November 21, 1994.

This marks the third year in a row with significantly unusual heavy snow in early winter.  Last year it was the snow onslaught of November 5-13, and in 2022 the city was buried in two major events in the first half of December.

https://ak-wx.blogspot.com/2023/11/south-coast-snowstorm.html

https://ak-wx.blogspot.com/2023/11/a-few-notes.html

https://ak-wx.blogspot.com/2022/12/anchorage-snow.html

With a snow pack of 10" in Fairbanks, this also marks the second earliest that both cities have recorded at least 10" on the ground at the same time.  The earliest was in the notorious autumn of 1992, but even then Anchorage didn't have sustained snow cover until October 27.

Here's a chart of snowfall through November 15 in Anchorage, with this year's total included through November 1.

The variability is enormous, and the change in 2020 really stands out compared to 2012-2019.  The only other period with 5 consecutive years of at least 10" in this early winter period was 1979-1983.

It seems unlikely to be coincidental that 2020 is when the PDO phase switched to negative, after 6 years of a mostly positive phase.

Here's a comparison of early winter snowfall with the PDO index in November:

There are some notable PDO extremes that coincide with snowfall extremes, e.g. high snow and negative PDO in 1955-56 and 2011, and low snow with positive PDO in 1957, 1986, 2002, 2014, and 2016.  However, the overall correlation seems to have been modest at best before the turn of the century - see below.  Since 2000, there's been a much better correlation.

One hypothesis to explain this might be that in earlier decades the positive PDO didn't prevent early winter snow, because it was still cold enough, but in recent years a positive PDO has brought greater warmth that has led to rain rather than snow.  More investigation would be required to explore this; but without doubt, the negative PDO regime is a snow-lover's friend these days in Anchorage.