Climate report says summer was warmer, drier than you may have thought
We’ve all heard the adage — weather is what’s happening now, climate is what happens over time. That is the case in the National Weather Service’s recent Alaska and Northwestern Canada quarterly climate outlook report.
The report covers observations and analysis of June through August and offers predictions for October through December. As with all the quarterly reports, there are snapshots of anomalies, synthesis and predictions of temperature and precipitation throughout the region, and writeups of significant events, like flooding and wildfires. In this particular report, there are also opportunities for recency bias in action.
Brian Brettschneider is a research physical scientist with the weather service in Alaksa who contributes to the quarterly reports. Though the data shows that summer temperatures and rainfall were overall pretty much normal in Anchorage and on the western Kenai Peninsula this year, residents might not feel like that’s the case.
“All summer long, I heard, almost on a daily basis, ‘Wow, this has been a really cool, rainy summer. And in reality, it was warmer than the vast majority of summers. And for most areas, it was drier than normal. … We compare against what we have become accustomed to. So, yes, it was cooler than almost every summer in the last decade but by historical standards, it was actually pretty warm,” Brettschneider said.
That’s recency bias — putting more weight on what we’ve recently observed.
“There were very few really warm days. So, for example, Anchorage only had 10 or 11 days where it hit 70 degrees, which is about five or days below what the historical average is, about 15 days per year," Brettschneider said. "And so I think people felt like, ‘Well, we didn’t have any long stretches of warm, sunny weather, so that meant it was a cool summer. Kind of interesting psychology, I think, goes into how we interpret the weather.”
Another example is happening right now — Southcentral entered a cold snap Sept. 21. Anchorage recorded the seventh-lowest temperature for the same timeframe in a 70-year period. And was in the bottom 10th percentile for cold with the most hard freezes for any year in almost the last 30. But the first two and half weeks of the month were pretty warm. So, when the next quarterly report is released, the temperature average might still show as normal.
“So it’s definitely cooler than normal, much cooler than normal, but because of the warmth the first two and a half weeks of the month, it may actually not show up very decisively in the final September maps about how we were, compared to normal,” Brettschneider said.
There’s also a pretty big change to keep in mind when interpreting these reports. The weather service uses 30-year chunks of time as the baseline comparison data for determining above normal, below normal and near normal temperature and precipitation. And that comparison timeframe just changed. It was 1980 to 2010, but now it’s 1991 to 2021. The more recent period is on average warmer than the previous, so new temps that used to rate as above normal are now in the new normal range.
“Historically, even though in Southcentral, we had a summer that was warmer than about two-thirds of summers in the last 80 or 90 years, it’s now actually considered about normal in comparison to our new climate regime,” Brettschneider said.
Looking ahead through December, forecasters predict another La Nina year, which typically results in colder and a littler drier than normal conditions for most areas of Southcentral. That’s not always the case, though. Last winter was wetter than normal.
Brettschneider says precipitation predictions are harder to nail down because precip is much more variable than temperature.
“Typical precipitation can vary wildly with local conditions — how close are you to the water, what are the nearby mountains, how are they oriented, how tall are they, what is the flow pattern typically,” he said.
Brettschneider says the three-month predictions, for a little colder and drier than normal in Southcentral, should be taken as a ballpark forecast.
“So it’s a guide, and the computer models, they do tend to lock into a La Nina pattern and kind of push out forecasts that reflect the historical conditions during those events, he said. "So, that’s our best tool at the moment, but the probabilities aren’t super high either way. So, that’s a long, roundabout way of saying, really anything is possible.”
As the other adage goes, if you want to know the weather, stick your head out the window.