Unusually warm September is obliterating Anchorage records – and the dry streak continues

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A birch tree is in full autumn mode in a valley near the Matanuska Glacier, Saturday, Sept. 15, 2018. (Anne Raup / ADN)

You're not imagining it: September's weather has been one for the record books, for both the warm weather and unusual streak of sunny days in Anchorage this month.

In terms of high temperatures, "we are absolutely smashing, obliterating, September records," said climatologist Brian Brettschneider.

The average maximum daily temperature so far this September is 65.9 degrees — more than three degrees higher than the next closest September in 1979, where the highest average daily temperature was 62.6, he said.

A three-degree difference is "just remarkable," Brettschneider said.

Typically, average high temperatures for September are 55 degrees, said Kaitlyn O'Brien, meteorologist with the National Weather Service.

High temperature records have been broken across Southcentral this month.

Even the daily low temperatures are above normal, Brettschneider said. "It tells you the air mass itself is very warm."

"It's a very strong bet that this will end up the warmest September on record," Brettschneider said.

Beyond the warm weather, Anchorage is also seeing an unusual dry streak.

This is the longest stretch Anchorage has seen in more than 100 years of dry September weather, Brettschneider said.

Whereas long dry spells are common in the springtime, August and September are usually Anchorage's wettest months. This year, August had above normal rainfall, Brettschneider said, with at least a trace of rain for 25 days in a row.

But the rain stopped on Aug. 26, and it hasn't been back.

Wednesday marks the 24th day in a row without any measurable rain (defined as at least 1/100th of an inch) in Anchorage — the longest dry streak since 1916 between the months of June 25 to Oct. 19, according to Brettschneider.

Those aren't the official records — records at the National Weather Services in Anchorage only include data from the Ted Stevens Anchorage International Airport, which go back to 1952, according to meteorologists there.

Brettschneider used data from several different records — from the Anchorage airport, Merrill Field airport, and downtown — which he strung together in his analysis.

According to the National Weather Service, the last time that September had a long dry streak similar to this was in 1984, when there were 22 days without measurable precipitation, meteorologist Kaitlyn O'Brien said.

All this fair weather is due to a high pressure system that's been hanging over Alaska.

Usually in September, "low pressure is the rule, not high pressure," Brettschneider said. A few days of high pressure system isn't unusual – "but to have (a high pressure system) parked there for such a long time is really uncommon," he said.

The best part? Dry September weather in Anchorage doesn't come with downsides seen during other parts of the year — there's no wildfire risk, or drought risk. "It's really kind of a win-win," Brettschneider said.

So, enjoy.

A new weather pattern is forecast to move into Southcentral this weekend, O'Brien said, likely bringing rain along with it.