Tuesday, December 29, 2015

Winter at O'Brien Creek

Back in 2012, before I took over as lead author on this blog, Rick Thoman penned a very nice essay about candidate locations for the coldest place in Alaska.  I've long been interested in his comment there that a short-lived co-operative observing site at O'Brien Creek in the Fortymile Country tended to be colder in winter than the famously cold settlement of Chicken.  After all this time I've taken a close look at the data, and I can confirm that indeed O'Brien Creek was (and presumably still is) slightly colder than Chicken in winter.  This would give it the coldest observed winter climate in interior Alaska.

The O'Brien Creek co-operative observers (Larry and June Taylor, to whom we owe a debt of gratitude!) recorded the weather at their place of residence from May 2001 through August 2010, giving us 9 winters of mostly complete climate data.  There are some missing days or periods here and there, but overall the November-March data is 94% complete for this period; this is about the same as for Chicken.

Looking at all dates for which data is available from both O'Brien Creek and Chicken, we find that the November-March mean temperature was 0.5°F colder at O'Brien Creek; so overall it is a very small difference, and not statistically significant.  However, the differences are larger in late winter and are strongly significant for both February and March.  The chart below shows the mean daily maximum and minimum temperatures by month for the overlapping period of record; we see that differences are very small in November through January, but O'Brien Creek is colder in February and has lower minimum temperatures in March.


The November-March mean temperatures for each winter with mostly complete data are shown below, with the top pair of lines showing mean maximum temperatures and the middle lines showing mean minimum temperatures.  The bottom pair of lines shows the differences between the two locations, with the scale on the right axis.  The winter of 2005-2006 produced relatively warmer daily maximum temperatures at O'Brien Creek, but in most of the other winters O'Brien Creek was slightly colder.  February mean temperatures were colder at O'Brien Creek in all but one winter, and in February 2007 the difference was a substantial 6.7°F.  The 2006-2007 November-March mean daily minimum temperature of -30.6°F is remarkably cold and ranks up (down) there with the likes of Umiat, Arctic Village, and Allakaket for historic cold.


It's interesting to look at the absolute minimum and maximum temperatures observed at the two locations during the period of overlapping data; see below.  As before, the green and black lines show the comparison for maximum and minimum temperatures, and the red and blue lines show the differences.  For November through January there are no obvious systematic differences, but from mid-February through March the extremes become relatively colder at O'Brien Creek for both maximum and minimum temperature.  So for example O'Brien Creek recorded -61°F on March 3, 2007, and -51°F on March 15, 2009, whereas the latest dates for -60°F and -50°F at Chicken are February 24 and March 4, respectively - and that's using the entire period of record at Chicken, which is now almost 20 years.


The tendency for cold late winter conditions at O'Brien Creek seems very likely to be a direct result of the steep nearby topography, which maintains long hours of shadow over the valley until well into spring.  The topographic map below shows the situation, with terrain rising up steeply in most directions, and the photo below (courtesy of Rick Thoman) further illustrates the nature of the surroundings.  The deep valley may also help shelter the valley floor from prevailing wind patterns, creating more frequent calm conditions.



The topographic map for Chicken (below, on a somewhat expanded scale) shows much less terrain variation in the vicinity of the station, and therefore it seems likely that both solar and wind-induced warming would have more of an effect on Chicken in late winter.  As cold as Chicken is, then, it is not ideally situated for cold, as the deeper valleys of the Fortymile Country are capable of producing even colder winters on average.


12 comments:

  1. The O'Brien Creek location resembles Tomtor in Yakutia.

    Gary

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    1. Gary, indeed it appears that Tomtor and Oymyakon are in a high-elevation valley: elevation 2400' at Oymyakon.

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  2. Nice write-up Richard. Google Street View follows the Taylor Highway all the way to Jack Wade Junction but then turns east along the Top of The World Highway. There's a DOT maintenance camp there. I wonder if they keep any records? I have a few pictures of there if you are interested. There is a large topographic obstruction to the south, immediately past the Fortymile River bridge.

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    1. Thanks, it's too bad the adventurous Google drivers didn't turn north to Eagle. Yes, I'd certainly be interested in photos - of the O'Brien Creek area you mean?

      I just noticed there is a RAWS (FMRA2) above the Fortymile River bridge but it's at 2100' on the hillside.

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  3. What's the resolution of the infrared sensors on the satellites? And can they be used to estimate the temp difference between Chicken and other colder spots?

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    1. It's sub-1km for the modern polar orbiters, easily enough to pick out cold spots. I would love to try it but I'm not very familiar with satellite data products. Perhaps you'd like to work on it? It would be fun to run through a number of winters to locate the true pole of cold; then take a hiking trip and install a thermometer in the winning location.

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    2. Not necessarily Alaska but as Rick mentions in a comment to the Blog cited above the area north of Old Crow in NW Canada, called the Crow Flats, typically shows IR white=cold when nearby scans suggest warmer surface temps. A recent example:

      http://pafg.arh.noaa.gov/arhdata/sat/hrpt/15361233140/4akf.jpg

      Old Crow Flats ecoregion:

      http://www.emr.gov.yk.ca/oilandgas/pdf/bmp_old_crow_flats_ecoregion.pdf

      Once it's cold everywhere then record cold probably becomes a function of observation station location. Still, keep a periodic eye on the IR shot of the Crow Flats this winter.

      Gary


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  4. Another comment off topic.

    With Anchorage now having no snow and all of the southern half of Alaska experiencing Chinooks, I wonder how the snow levels along the standard Iditarod trail are doing. And based on last year, can we get a probability of the Iditarod coming to Fairbanks again?

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  5. McGrath was still at 18 inches snow depth yesterday but the forecast looks very warm. This pattern change is certainly ominous for overall snow levels.

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  6. Hi: Meant to write sooner, but time moves on and I often don't. I had the good fortune to work in the Fortymile country and spent many pleasant times staying with the Taylors at their rental cabins. June was a great cook and Larry was always up for an adventure, whether it was going out on the snow machines at -30 or a boat trip up the Fortymile River to the "kink". His spirit belied his age. Unfortunately, he passed on after a short illness this past October. He will be missed by all who had a chance to stay with the Taylors.
    Anyway, I had a question, maybe an idea for a new post. It seems like the extreme cold spells, -50 to -60 no longer occur with any great frequency like they apparently did in Fairbanks thirty to forty years ago. When I first moved to Fairbanks, I remember hearing stories of square tires, frozen batteries, and broken car door handles that occurred whenever it got down to -50 for any length of time. Well we haven't had an extreme cold spell here in awhile now; the only real cold spells I can remember are Feb.'79 and Jan. '89. So maybe you can run your fancy statistics program and see what's what. Thanks for your time. Jon

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    1. Hi Jon, thanks for the comment. I'm envious of your time with the Taylors out there in the country. For my part, I enjoyed simply going through the high-quality written observation forms that they produced!

      You're certainly right that the most extreme cold no longer occurs in Fairbanks, or at least it's very much less frequent. The last -60F was measured in January 1971. But -50 occurred in 2006 and 2012, and interestingly Jan 1989 and Feb 1979 "only" reached -51; but they had a lot of -45 days (12 and 11 days respectively). So it may be at least as much the length of cold spells that has changed.

      In any case, here's an earlier post on the decline of extreme cold in Fairbanks. I'll see what else I can come up with.

      http://ak-wx.blogspot.com/2013/12/deep-freeze-temperatures-aloft.html

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    2. That post just about covers it. I didn't read your blog back then, so missed it.
      Seems like 1971 was the last "extreme" cold spell when it went well below -50 for any length of time. While the 1979 cold spell did beak some records, the 1989 cold spell didn't break any (if I remember correctly). Since then it seems like the cold spells just don't last very long (not that I'm complaining). My guess it's due to changes in wind patterns, jet stream, or the polar front, likely from ocean warming, El Nino, or whatever, that prevent the deep high pressure systems from establishing themselves over interior Alaska. While it maybe true that global warming is here to stay, I'll still keep splitting 6-7 cords of wood every year. Thanks.

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