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.

Winter Hangs On

Unusual cold is hanging on with remarkable tenacity in Alaska this winter, and last night saw temperatures worthy of the depths of winter in many locations.  Here are a few examples of notable low temperatures today:

-50°F  Bettles
-45°F  Tanana
-44°F  Chalkyitsik RAWS
-42°F  Nenana

And in and around Fairbanks:
-46°F  Salcha RAWS
-41°F  North Pole
-39°F  Goldstream Creek
-39°F  Smith Lake at UAF
-38°F  Fairbanks airport

Here's the temperature trace from the past two weeks at Smith Lake (UAF's North Campus).  The temperature did not break -10°F today, which is pretty impressive for the time of year.

Of course clear skies at this time of year produce large diurnal temperature ranges, as seen in the Smith Lake data.  The Chalkyitsik RAWS (about 20 miles east of Fort Yukon) often produces spectacular examples, and just the other day this site saw temperatures vary from a low of -49°F on two consecutive nights to a high of 0°F in the intervening day.  When looking at days with a high temperature of 0°F or below, this is the largest diurnal range on record for the site (data since 1997).

The chart below shows daily Chalkyitsik temperatures so far this winter, as compared to seasonal normals (obtained from the 1997-2018 history).

Two features are striking: the persistence of unusual cold since mid-December, and the expansion of the daily temperature range since early February.  The latter is entirely in keeping with climatology, which shows a pronounced rise in the average diurnal range in late winter; in fact it's remarkable to see the normal high temperature bottom out very soon after winter solstice, while the normal low temperature doesn't show any meaningful rise until well into February.