Even with lag, Alaska passing
By Ned Rozell
July 11, 2007
You may not have noticed it as you were scooping fish out of
the Copper River, or riding your bike through the tawny light
of 10 p.m., but Alaska just made a left turn toward winter.
Much of the state will soon reach the average yearly date when
the air won't get any warmer. In Fairbanks, on July 19, the average
daily temperature based on about a century of records drops from
63 to 62 degrees Fahrenheit. Anchorage, because the ocean is
nearby, starts cooling later, on July 29, when the average temperature
drops from 59 to 58 degrees Fahrenheit. Chandalar Lake reached
its heat peak about July 15. Adak and Shemya in the Aleutians
are two of the last places in Alaska to give in, with their average
temperatures not dropping until late August and early September.
A person might think that since we get our maximum sunlight on
the summer solstice (on or about June 21), we should also get
our peak warmth then. The sun's calling the shots, right?
The sun sets on Alaska's
summer, over the Fish River near White Mountain
Not entirely, said Martha Shulski of the Alaska Climate Research
Center at the University of Alaska Fairbanks.
"We're warmest a few weeks after the solstice," she
A lag exists between the peak of solar energy input and the warmth
we feel. It's a phenomenon that also shows up in winter, and
when people's pipes freeze mysteriously in May.
"You see (the lag) in a lot of different places," Shulski
Temperatures peak several weeks after we get the most sunlight
because the ground absorbs energy from the sun and releases it
to the air. This "longwave radiation" from the earth
increases after summer solstice because the ground is slow to
release the potent solstice-time energy. The day the heat emitted
by the surface starts decreasing is usually the day we start
feeling cooler temperatures.
The seasonal lag in temperatures is similar to one that happens
every day in summer, Shulski said, when our thermometers don't
hit their maximums until a few hours after we receive our peak
"Solar noon (in Alaska) is 2 p.m. and our daytime high is
usually three to four hours after that," she said.
This stall pattern also exists in winter, when temperatures are
coldest in January, a few weeks after winter solstice. And, as
Charles Deehr and Neil Davis noted in this column in 1976, there
is a long delay between the
coldest air temperatures and the time that cold penetrates deepest
into the ground. The soil temperature 18 feet below the surface
drops to its coldest in May, they reported.
Back to the turning point of summer, why do Chandalar Lake and
Fairbanks reach their peak of warmth faster than Anchorage, Juneau,
Ketchikan, and other places near the ocean? The presence of a
large body of water makes a big difference, Shulski said. In
a place like Anchorage, the ocean absorbs much of the energy
that the ground is converting to heat in landlocked areas like
Here's some dates for the crest of summer warmth from information
supplied by the Alaska Climate Research Center: Chandalar Lake,
July 15; Fairbanks, July 19; Galena, July 21; Valdez, July 26;
Anchorage and Whittier, July 29; Prudhoe Bay, July 30; McCarthy,
July 31; Kenai, Aug. 2; Juneau, Aug. 11; Kodiak, Aug. 12; Seward,
Aug. 13; Yakutat, Aug. 18; Adak, Aug. 29; and Shemya, the land
of endless summer, Sept. 3.
But don't say goodbye to summer just yet. These numbers are long-term
averages that match daily reality only during extreme coincidences.
An Alaska parcel of air near you is prepared to defy the long-term
average by being extra hot. Or maybe unusually cold.
According to Gerd Wendler,
Professor of Geophysics, the temperature peaks in Ketchikan
between July 25th and August 15th. For this time period the mean
long term (1971-2000 normal) temperature is 59°F. Somewhere
in the middle of the time span the highest temperature can be
This column is provided as a public service by the Geophysical
University of Alaska Fairbanks, in cooperation with the UAF research
community. Ned Rozell is a science writer at the institute.
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