The new climate normal
ANCHORAGE, Alaska (KTUU) - It’s not unusual for a meteorologist to say a temperature or snow total is above or below “normal.” But what is normal and how is that decided?
In terms of weather, the “normal” is based on long-term climatological trends established by looking at a three-decade average.
“The climate normal period is a 30-year block of time, that is supposed to represent the current state of the climate for wherever you are,” said Brian Brettschneider, research climatologist with the National Weather Service Alaska Region. Every 10 years, those decades change to keep up with the changing environment.
Daily and monthly normals are established for temperature, precipitation, heating and cooling degree days, frost/freeze dates, and growing degree days at about 9,800 stations across the United States operated by the National Weather Service.
For the past 10 years, the three decades used to establish “normal” have been the years 1981 to 2010. The transition into a new decade on Jan. 1 also means a new “normal” will be established by now looking at the conditions from 1991 to 2020. With the changing of the decades, our climate “normals” are going to change. It will literally be the “new normal.”
“Here in Alaska, we’ve known, quite clearly for a while that we’re warming. Alaska is warming, and every part of Alaska is warming,” said Brettschneider. “And so it should come as no surprise to anyone who’s watching that we expect the 1991 to 2020 period to be warmer than the 1981 to 2010 period. And the real question is, well, what’s driving that? And what time of the year would we expect that?”
A major contributing factor to the warmer temperatures in Alaska is the lack of sea ice. This is mainly visible during autumn and to a lesser degree in spring. North and west portions of Alaska will likely see the biggest changes to their climate normals because of the changes in sea ice coverage in late fall and early winter.
Daily high normals for Utqiagvik are expected to rise by more than 5F degrees during much of November. During the months of October and November, Anchorage’s new monthly high-temperature normals will likely go up by almost two degrees.
Another month to see a large increase in our normal temperatures in Anchorage is July.
“Of course, July 2019, we not only did we set our record for July but our record for any month, and we just totally blew past it,” added Brettschneider. “We also had very warm for you in July in 2013 and 2015. So you know, adding a couple of the warmest on record and the very warmest, has really shifted that up.”
But not every month is warming. Anchorage’s new monthly highs for January and March will be slightly cooler (less than 1 degree).
“Remember, these 30-year periods have 20 of those years are overlapping,” said Brettschneider. “So really, what we’re doing is we’re crossing out the 1980s and we’re swapping those in with the 2010s ... For example, with January, being a little bit colder, we had some very warm Januarys in the 1980s. Those are now gone. And we had two of our coldest Januarys on record. January 2012 and January 2019 are now included. And the same thing with March we had some of our very coldest Marches on record have occurred in the last decade.”
Snow and rain
Snow lovers will be happy to hear Anchorage has been gaining snowfall. The new normal shows a bump in snowfall, up about 2.2 inches annually to 77.48 inches. But the snow is falling at different times during the year.
Brettschneider explains, “We’re seeing quite a big decrease in October and November snowfall, but a big increase in January, February and March snowfall. So in the net effect, the effect of that is we’re bumping up our snow totals so we’re bucking the trend of most places and we’re going to be the beneficiary of more snow.”
Precipitation overall is also going up slightly but the timing is changing. August used to be the wettest month in Anchorage. August lost some ground rain-wise and September gained precipitation. September is now the wettest month of the year on average.
The new climate normals have yet to be finalized and the data used in this story is preliminary. The final release of the new climate normals will happen sometime after May. The National Center for Environmental Information calculates the data from approximately 9,800 stations across the country. According to Brettschneider, they will also do quality control checks on the data and comparisons to surrounding recording stations before finalizing our new climate norms.
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