Thursday, December 3, 2015

Snowy November

November was a remarkably snowy month in parts of the interior, with Bettles setting a new record for total November snowfall at 50.6".  This is only the second time that any calendar month has produced more than 50" of snow in Bettles; the record was 55.8" in January 1973.  In McGrath the monthly total was the second highest for November at 44.6".  The chart below shows the winter-to-date accumulation of snowfall in Bettles compared to the historical range; this winter is running at a record pace, although interestingly the snow depth of 19" is not much above the normal of 15" for this date - the melt-off in October had a lot to do with this.

In looking at the historical distribution of autumn and early winter snow in Bettles, I noticed a surprising absence of large outlier snow totals in October, especially considering how wet Bettles is compared to Fairbanks.  As the chart below shows, the distribution of total precipitation in Bettles is strongly skewed in both October and November, with quite a number of very wet months.  However, total snowfall shows remarkably little skewness in October (second chart below); only 5 Octobers have exceeded 21" of snow, which is the same as in Fairbanks over the same period, although Bettles is almost 50% wetter on average for the month.

The scatterplots below show the joint distribution of October precipitation and snowfall for Bettles and Fairbanks.  It's interesting to observe that Bettles shows a less good correlation, and in particular many of the largest precipitation totals have been associated with relatively modest snowfall totals.

The ratio of snowfall to precipitation provides another look at what is going on (see below): the wettest Octobers in Bettles reliably have low snow ratios, which implies that plain rain accounts for a significant fraction of the precipitation in these wet months.  In the 10 wettest Octobers since 1951, 49% of the precipitation fell on days with a snow/precipitation ratio less than 5.  However, in Fairbanks there are fewer very wet outliers, and the tendency for reduced snow ratios is not as evident; only 31% of the precipitation occurred on days with a ratio less than 5, for the 10 wettest Octobers.

We can conclude that Bettles is more prone to heavy rainfall events in October than Fairbanks, even though Bettles is more than 5°F colder on average, and normal daily mean temperatures are below freezing even by the first of the month.  I find this quite surprising.

The parallel charts for November show a much tighter relationship between precipitation and snowfall amounts, as expected, because rain becomes unusual in both locations in November.  Nevertheless, it's interesting to see that even in November, Bettles often sees a snow/precipitation ratio of 10-12 or less, suggesting wet snow, whereas Fairbanks rarely sees a ratio much below 15 as the snow is usually less dense.


  1. I suggest Bettles is at the eastern receiving end of a W>E moisture advection triangle. The base is formed to the west approximately by Unalakleet and Kotzebue (with some potentially from the Lower Yukon to the southwest). The Kobuk and Koyukuk river drainages offer low terrain interference and in fact may help focus flow.

    Whereas for Fairbanks it is further from an oceanic influence and has some interfering terrain to the west and south unless the advection follows the Galena to Fairbanks short path up the Yukon and Tanana Rivers.

    An examination of seasonal wind patterns and reports from other wx stations to the west may clarify this theory.


    1. Someday I'd like to investigate the dynamics of snow production in that I mean vertical temperature and precipitable water conditions conducive to the creation of falling snow. Isn't that what's in question here?


    2. Yes, the temperature and moisture characteristics aloft are critical for determining the type of snow or other hydrometeors that fall, so it's the airmass characteristics above Bettles and Fairbanks that are responsible for the differences noted here. The idea that Bettles has a more "maritime" climate in this respect is interesting, because I think of their climate as being highly continental (based on the temperature normals).

      I found some interesting NOAA/NWS internal tutorials on snow ratios that you might find useful, Gary. It's a large and thoroughly-researched topic.

    3. Thank you for the learning links Richard. It's those new topics that make this Blog very interesting.

      The suggested "seasonal maritime" influence for Bettles is possible, and might be confirmed if any advective potential (and resulting overrunning +moisture/temperature) from W>E per my earlier post were examined. That hypothesis is roughly based upon observation from having travelled the area and talking with others that lived there.

      Fall storms with a maritime source commonly move onshore from the Bering/Chukchi Seas and can affect both Fairbanks and Bettles (and western Alaska in general) starting in September. Reanalysis may confirm that scenario over time, especially as it pertains to rain versus snow or the snow/precipitation ratios you present.

      Any recent yearly delay in the onset of seasonal ice cover may enhance that effect.


    4. Recent analysis of sea ice cover for November 2015, potentially in support of my last comment:


    5. Here's a personal communication fill from Andy Greenblatt ( who grew up and has spent countless hours in the Bettles area.

      The Fall snow weather typically comes from the west in association with Low pressure cells, proceeding first up the Kobuk River W>E, across the intermediary Alatna River and Norutak Lake plateau, then up the middle Koyukuk River to the Bettles area. It occurs heavily at the interface of colder air, either below or to the east, and can be precipitated by rising terrain. Due to circulation, the snow may initially come with SE winds that later shift direction depending upon the location and wind flow associated with the system.

      Some localized drainages surrounding Bettles get more snow...the Big Salt River, a SE flowing tributary to the Yukon west of the Yukon bridge to the south of Bettles was mentioned as an example. It's surrounded by hills to the SW in the path of incoming weather systems, a good candidate for the creation of snow. A local homesteader kept meticulous records of snow depth that Andy referred to.


    6. Thanks for the extra info Gary (and Andy). Would be fascinating to see the Big Salt River snow depth records if they are anywhere to be found.

      I don't doubt that the general description of snowfall development and progression is correct, as it matches the typical general movement of upper-level flow features in disturbed weather scenarios. Illustrating the specific trajectory of moist airflow with available weather data would be a tricky task, however. Streamflow contours in the reanalysis data might do it, I suppose.

      While we're on the topic of snow near Bettles, I'll quote here a recent conversation from Brian's Facebook page (since it's already in the public domain). For reference the record snow depth in Bettles is 86" (in April 1963); in January 1993 it reached 59". In an average winter it reaches 37".

      Jack Reakoff: In the 1992-93' winter there was 7.5 feet of snow standing in our yard in in mid-January... a (mean measurement of three) I took on snowshoes. The snow was very dense when settled to 5.5 feet in March...enough to hold cow moose...50% of the moose had died by February though. The deepest snow the old-timers here in Wiseman knew of in the oral record was 6.5 feet in about 1950-51' winter.

      Alaska Climate Info: There's no data for Wiseman between 1952 through 1996, but the deepest snow depth on record for your location was 79" between February 27, 1920, and March 2, 1920.

      Jack Reakoff: Too bad the snotel was not in Coldfoot fro the 92'-93' winter...Coldfoot will have about 10-20% less snow than Marion Creek 5 miles up river...The Marion creek area of the Middle Fork Koyukuk River has 4500' to almost 6000' mountains on both sides of the valley. The South end of the Brooks Range in the Koyukuk drainages will uplift and unload a lot of moisture. The Alatna and John Rivers can have even more snow than over here, at the same feature latitude.

      Alaska Climate Info: Jack Reakoff Fascinating. Thanks for sharing your insight.

      Jack Reakoff: Alaska Climate Info I trap up and down the Middle Fork Valley so have waller-ed in a lot of deep snow for the past 35 years.

      Rick Thoman: There is monthly snow course data from Coldfoot starting in 1971. In 1993 the Feb 01 snow depth there was 50", 51" Feb 24th and 59" Mar 31st.

    7. Jack's sister is the Cooperative observer in Wiseman. Between the two of them, there's a lot of local knowledge about snow in that part of the state.

      If anyone is interested, here are a couple of posts I did (FB) showing the greatest seasonal snowfall and snow depth. The first link is where Jack added comments about historical snow season.

      Greatest seasonal snowfall:
      Greatest snow depth:

      Richard, you are always welcome to reference one of my FB posts or link directly to them from the Deep Cold blog.

    8. Thanks Brian. Your posts were excellent and I thought it was worth preserving Jack's comments here for future reference.