Tuesday, March 23, 2021

Big Diurnal Range

This is the time of year for very large temperature swings between day and night across interior Alaska.  Skies are often clear and the air tends to be very dry, allowing for rapid cooling at night but strong solar insolation during the day.  Deep snow pack of course facilitates overnight cooling, with very little of the daytime solar input being stored at the ground surface.

The automated observing site on the Salcha River often produces some of the most spectacular diurnal temperature ranges, and the last 10 days have been quite extreme in this regard.  All but two of the last 10 days have seen a day-night temperature swing of more than 50°F, and March 14 saw an amazing 65°F range.

The hourly temperatures on March 14 ranged from -36°F at 7am to +29°F at 3pm, and then back to -31°F by midnight.


The largest diurnal range ever measured by the Salcha RAWS was 69°F, on both March 30, 2006, and March 16, 2002.  The site averages close to a 40°F diurnal range in mid-March.  For comparison, the normal range at Fairbanks airport is not quite 30°F in mid-March, although Fairbanks had a day-night swing of 48°F just yesterday.

Out of curiosity I looked at long-term normals from global gridded temperature data (derived from actual station observations), and according to this data the largest "normal" diurnal range found anywhere in the world is in central Oregon in late August: with an average low of 35°F and an average high of 79°F, the normal daily range is 44°F.  I wouldn't be surprised if this is exceeded in some desert areas with sparse observing networks, but nevertheless it shows that Salcha's typical ~40°F range is near the upper end of what's observed anywhere on the globe.


  1. The largest daily range of temperature (tx-tn) in Iceland (°C) [automatic network, 1996 to 2020]. I have not checked all of the numbers, most are probably ok, but one should - in the spring - with snow on ground be aware of the possibility of a "false" tx - as seen here in the April value (which I have to remove from the record) - an almost certain case of reflected shortwave radiation hitting the bottom of the thermometer screen (cylinder). This particular station [Dyngjujökull] is located on a glacier surface - as is the station Brúarjökull B10 - the values there [March and May in the table] might be doubtful for the same reason [but I have not checked]. I don't know how you deal with this in Alaska - but I know that it really is a potential problem with the small cylinder screens in such extreme radiation surroundings.

    1 4830 2017 1 14 1.9 -24.7 26.6 Möðrudalur
    1 4300 1998 2 12 0.5 -27.5 28.0 Mývatn
    1 5932 2008 3 4 4.2 -25.9 30.1 Brúarjökull B10
    1 7790 2020 4 28 14.9 -13.5 28.4 Dyngjujökull
    1 5932 2013 5 2 3.3 -21.7 25.0 Brúarjökull B10
    1 1596 2012 6 2 22.6 -0.9 23.5 Þingvellir
    1 1596 2008 7 30 29.7 6.0 23.7 Þingvellir
    1 4614 2004 8 13 27.2 2.8 24.4 Ásbyrgi
    1 4271 2017 9 1 26.4 2.9 23.5 Egilsstaðaflugvöllur
    1 4830 2005 10 14 7.6 -17.8 25.4 Möðrudalur
    1 4300 1996 11 26 4.4 -20.6 25.0 Mývatn
    1 5933 2015 12 26 0.2 -25.3 25.5 Kárahnjúkar

    The record daily range in Iceland (manned stations also) is 33.9°C - but that was in an "advective" situation, change of airmass. Differences of more than 25°C are rare. In Reykjavík the daily range maximum is "just" 18.7°C and more than 15°C is very seldom seen.

    Best wishes, Trausti J.

    1. Thanks for your reply and for the interesting comparison. Yes, maximum temperatures reported at the U.S. RAWS sites are known to be too high in calm and sunny conditions, so I am sure this contributed to the extreme diurnal range. Some years ago I did some analysis of the effect:


      Of course the direct solar radiation is not yet as intense as in early summer, but as you note the reflection from snow may add to the problem.

    2. Rick, thank you for the link to your earlier blog (that I recollect when I see it). We have noted the aspiration problem here in Iceland quite well. The measurement of maximum (and minimum) (air) temperature can be a difficult problem to solve, as soon as I begin to think about the details I suddenly find myself sinking into questions that are more of a philosophical nature - how to define a maximum temperature - how far should you go in defining and pursuing "standard conditions" etc. Extreme temperatures tend to occur in situations when "disturbing factors" tend also to be "extreme" in some sense. To get a hold on these you have to do some site-specific micrometeorological investigation - which is utterly impractical to do. We are in a way lucky here, cause we do not use the max and min for calculating monthly mean temperatures (we have other problems).

  2. https://mesowest.utah.edu/cgi-bin/droman/station_total.cgi?stn=SLRA2&unit=0

    Here's the Salcha RAWS station info and location map. There's ample opportunity for daily insolation exposure followed by cold air advection down surrounding terrain and river bottom during the night. It's common to see wood smoke from heating stoves head towards lower terrain as it cools, then in reverse direction as it warms when sunny.


    1. Thanks. It's certainly a special location for cold air drainage/pooling.

  3. Looking at those low temps in the middle of the month, this has been one cold March!

  4. Looking at those low temps in the middle of the month, this has been one cold March!