Ask a Climatologist: What’s with all the rain?

A rainy day in Anchorage on Tuesday, Aug. 10, 2021. (Matthew Faubion/Alaska Public Media)

Sunday was the rainiest day Anchorage has seen in almost six years.

Meanwhile, parts of Western Alaska recently saw their wettest month on record, and forecasters are expecting an atmospheric river to soak Southeast.

National Weather Service climate researcher Brian Brettschneider, back for our Ask a Climatologist segment, says some areas have seen truly remarkable rain this summer. And for others, it just seems that way.

Listen here:

Brian Brettschneider: So the rainfall we had on August 8 in Anchorage was 1.25 inches for the calendar day. That was the most rain we’d had on a calendar day since September 2015. So even though August is the rainy season, that still is a large rainfall event. In 70 years at the airport, there’s only been 22 times when more rain fell on a calendar day. Now, August and September are the rainiest months of the year. But it normally isn’t coming in that big of a punch in one day.

Casey Grove: And, anecdotally, people have been talking about it being a somewhat rainy summer, at least cloudier than the last few. But in terms of rainfall, is that true? I mean, are we even having a rainy summer?

Brian Brettschneider: Well, again, here in Anchorage, even with that largest rain in almost six years, and then another half-inch two days later, that has brought us almost to the normal amount of rain for the summer so far. So we’re actually a little bit below normal for rainfall just for the summer — for the June, July and August period.

Casey Grove And of course, people in other parts of Alaska will laugh at this and say, ‘That’s not even rainy by our standards.’ And down in parts of Southeast Alaska, I saw that there was a possibility of an atmospheric river? What’s going on down there?

Brian Brettschneider: Well, stepping back to Southcentral for a moment, you know, Anchorage averages about 17 inches of precipitation a year. So that’s rain and melted snow. So in three days we had 10% of our annual precipitation. So that’s a lot if you think about it in terms of percent. Juneau averages about 65 inches, I think, of precipitation a year. So if they had six or seven inches of precipitation in three days, it would be about the same ratio of average annual precipitation. So it does help to think of it in relative terms.

But yeah, down in Southeast, they are expecting an atmospheric river. As we speak, there’s a flood watch in effect for most of Southeast Alaska, from Yakutat down to approximately Sitka or just south of Juneau. And some of the models are showing six to 10 inches of rain in the northern part of the Panhandle around Yakutat, and four or five or more inches around the Juneau area.

Casey Grove: Remind us, what can folks expect with a large amount of rain like that in those communities?

Brian Brettschneider: It’s all going to depend on how much falls and over what period of time. But certainly, with the flood watch in effect, there’s a concern that rivers may rise, which could cause erosion or could cause road closures. Of course, there’s a lot of concern about mudslides given what happened the first week of December. I’m sure a lot of people are going to be looking really carefully at those slopes to see if there’s any indication that the rainfall is making them unstable.

Casey Grove: And what about the rest of the state?

Brian Brettschneider: We sometimes lose sight of the fact that the west coast of Alaska had record to historic rainfall in the month of July. Kotzebue had their wettest month on record. And they have records going back a long way. Nome had one of their wettest months on record. Prior to last week, it was fairly dry in the eastern half of the state. It was a different story in Western Alaska. They were getting hit day after day with heavy rain, particularly the last half of the month of July.

Alaska Public Media

Alaska Public Media is our partner station in Anchorage. KTOO collaborates with partners across the state to cover important news and to share stories with our audiences.

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