Most of Alaska saw a rapid warm-up at the end of last week. As a Chinook wind swept into Anchorage, record-high temperatures hit the city on Friday and Saturday.
Snow melted. Puddles formed. Streets iced over. Jackets were ditched, as one day in the 40s stretched into four in a row. And National Weather Service climate researcher Brian Brettschneider says that hasn’t happened in Anchorage in about a decade.
There are plenty of nicknames for meteorological or climatological phenomena, but Brettschneider — back for our Ask a Climatologist segment — says the Chinook event in Anchorage is not to be confused with a Pineapple Express, or the atmospheric river that slammed Southeast.
Listen here:
The following transcript has been lightly edited for clarity.
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Brian Brettschneider: So a Chinook wind is local to having a mountain range nearby where, you know, winds kind of accelerate down the mountain and they heat up as as they compress. And that’s kind of a local phenomenon that’s embedded in a larger pattern of kind of southerly warm flow. So here in Anchorage we’ve had a multi-day Chinook event. And it’s kind of ebbed and flowed in its intensity. But again, that’s kind of local to having mountains nearby, the flow coming from a certain direction over the mountains. When we talk Pineapple Express, we use that in the context of atmospheric moisture. So in Southeast Alaska, they were kind of under the gun of, what we call, an atmospheric river, or what people used to call a Pineapple Express. Again, that’s a moisture thing. That’s separate from the warmth that we’ve been experiencing in the central part of the mainland.
Casey Grove: Gotcha. It seemed like it just swept in really quickly. And by Friday night, things were just melting rapidly. Is there anything exceptional about how quickly that happened, or any way to kind of measure that?
BB: Well, it’s interesting, because especially here in Anchorage, when we get a Chinook flow, there’s often what I call a “Chinook front.” That’s the exceptionally warm air that’s coming down off the mountains, and that overtakes the cooler air that that was in place. And we saw, actually, a couple places in town, notably Merrill Field, an 11-degree jump in temperature in one minute. So these automated stations, they grab a temperature reading every one minute, and it jumped 11 degrees from one minute to the next, which was the largest one-minute jump at any of the automated stations in Alaska in almost a year, anywhere in the state. When we look out over longer time periods, I did an analysis of all the stations in the entire U.S., and Anchorage is pretty far up the list in how often we can get these quick temperature changes in short periods of time. So it’s not uncommon in terms of a rare event, but uncommon in the intensity and the rapidity of that change.
CG: Is there anything climatologically relevant about this in that, you know, you see these events happening more often or they’re more intense as the global climate warms?
BB: Well, you know, when we have these Chinook events in Anchorage, every single time, people ask me, ‘Hey, are these more common? Are these more intense? Are they different than they used to be as kind of a fingerprint of a changing climate?’ And the rather unsatisfying answer is that it’s just really hard to tell. There’ve been changes in instrumentation. How do you define a Chinook is even, you know, one place to start. If you say, well, a Chinook has to have a temperature of 40 degrees and has to have a wind in a general southeasterly direction at a certain speed. We can start to narrow in on it, but as best as we can tell, there may be a small increase in the rate and intensity of Chinook events, but it’s a pretty weak signal.
Casey Grove is host of Alaska News Nightly, a general assignment reporter and an editor at Alaska Public Media. Reach him at cgrove@alaskapublic.org. Read more about Casey here.
