Wednesday, October 28, 2015

The Inevitable Arrives

Winter is now right on the doorstep in Fairbanks, as October's remarkable stretch of stable, mild temperatures is about to come to an end.  Accumulating snow appears likely tomorrow and at various times in the next week, and temperatures will drop sharply by the weekend.  The only unusual aspect of this is that it hasn't happened already; the normal low temperature will be down to +3°F by Sunday.

Fairbanks airport has not yet seen a single day with a high temperature at or below 32°F, and this breaks the 1930-present record for latest first occurrence of such a day (previous record October 27, 1938).  Of course it very nearly happened several weeks ago, when the high was 33°F for 3 consecutive days (Sep 29 - Oct 1).  Also I don't believe there are any other stations in the Fairbanks area that remain without a sub-freezing day; Fairbanks airport has been an island of warmth.

The chart below shows how unusual the warmth has been lately, with daily mean temperatures remaining more than 1 standard deviation above normal for 13 consecutive days (including today).  Reader Mike noted that there was actually no downward slope to temperatures for a several week period ending October 23; this was true for up to a 30-day period ending on that date.  It is unusual to have such a long period of stagnant temperatures at this time of year, but not extremely so; there have been a number of other years with similar occurrences, such as in 1938 when the temperature showed no decline for a 40-day period ending October 26.

A more unusual aspect of recent temperatures has been the sheer lack of variation; it has not been cold, but neither has it been extremely warm, and lately each day has been much the same as the previous one.  The lack of variance is actually unprecedented for the time of year, as the chart below demonstrates; in other words, the 30-day running variance is lower than ever observed before on this date.  Remarkably, it was lower recently than at any point during summer, which is usually when temperatures are least variable.

Looking at the long-term history of variance at this time of year reveals no obvious trend over the full climate record (see below; the dashed line shows the long-term median).  But it's interesting to note that low variance has been more common since the mid-2000s, and the last 3 years have all been notable in this regard.  Of course this goes along with a tendency for cold in late September and relative warmth in October.

Finally, for future reference, here are a few webcam photos from today to document the state of freeze-up at a few locations:


  1. Richard,

    As we move closer to freeze-up in many locations (and in light of the FAA webcams you have been showing) I thought I'd share what might be the best river webcam in the state, from my hometown of Bethel:

    1. Very nice, Andy. Thanks for sharing! It will be fun to watch.

  2. Finally put on my winter coat after weeks of September like weather this October.

    Snow first melted then froze on Fairbanks' warm roads = slippery ice base for the winter. Now we finally have the start of surface insulation and increasing albedo at an already low angle of the Sun.

    We call it Winter.


  3. Are there any weather patterns that create such stable conditions? Or is this flatlining of temperatures just somewhat random?

    1. Eric, the answer (to the first question) is certainly yes - for example El Nino brings more stable flow patterns and temperatures to Alaska in winter, and the positive PNA is more stable than the negative PNA. It would be interesting to flesh this out with more research, e.g. is there an overall inverse correlation between temperature anomaly and variance?

      Having said that there is also undoubtedly a good deal of randomness in these sub-seasonal variations.

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