Official weather observers at Ted Stevens Anchorage International Airport recorded the city’s fourth day of thunderstorms for the year on Monday, pushing this year’s storm count further above average, according to the National Weather Service.
The city typically has one or two days of thunderstorms each year, according to weather service data from the West Anchorage airport. So far this year, the weather station has recorded four: May 16, June 3, June 5 and Monday.
So, what’s causing this summer’s string of storms?
Generally, four ingredients: sun, mountains, moisture and the right wind, according to Gene Petrescu, Anchorage-based regional scientist for the weather service. Sunny, clear skies during the daytime heat up the mountains, warming the air near the surface and causing it to rise.
“If the temperatures and conditions above the mountains aren’t too warm, then it becomes unstable,” he said.
That sets the table for thunderstorms to develop over the mountains, and if the wind is right, they’ll blow over the city.
Anchorage most often sees thunderstorms in June, July and the beginning of August, said Brian Brettschneider, research associate at the University of Alaska Fairbanks International Arctic Research Center.
Brettschneider has combed through weather service data from the Anchorage airport, and found just one year since 1960 with more than four days of thunderstorms. In 2005, there were six days of thunderstorms, he said. In 1980 and 1998 there were four days of thunderstorms. Last year, he said, there were two.
There were 18 years without any days of thunderstorms, Brettschneider said. He calculated an average of about 1.4 days of thunderstorms a year.
Petrescu and Brettschneider said it’s impossible to say whether the count of thunderstorm days so far this year is indicative of a larger trend. The numbers are too small to draw broad conclusions, Brettschneider said.
This year’s tally of thunderstorm days in the Chugach Mountains around Anchorage is also on pace to surpass average, Petrescu said. Normally, there are seven to nine days of thunderstorms in the mountains each year. Already, there have been at least eight and it’s not even mid-June, he said.