The autumnal equinox Tuesday night marks the official end of summer.
And while temperatures have been slightly warmer than what's considered "normal" for this time of year, Rachael Fewkes, a meteorologist with the National Weather Service, said Monday was Spokane's "last warm day."
The forecast for Tuesday and Wednesday stays dry with highs in the upper 70s Tuesday. Temperatures the following day should dip into the lower 70s.
"Thursday and into the weekend, our pattern starts to become more active and a little more fall-like," Fewkes said. "We'll see a weather system move in that's going to bring even cooler temperatures, with afternoon highs dropping into the upper 50s to low 60s by the weekend."
She said rain may follow that drop in temperature. The cooler weather system should start to move into the Cascades on Thursday afternoon, but will become "more widespread across the region" by Friday morning. She said there's a 40% to 60% chance that the Spokane area sees at least one-tenth of an inch of rain between Thursday evening and Saturday morning.
In the Cascades, Fewkes said snow should begin to fall between the 5,000- and 6,500-foot elevation range. Wind speeds in the Spokane area are expected to stay mild for most of this week, but could swell up to gusts of 30 mph for Friday and Saturday.
As for temperature lows, Fewkes said Tuesday through Thursday, Spokanites should expect temperatures to be in the upper 40s to low 50s at night.
"Saturday morning is when we'll see a pretty decent drop in low temperatures," Fewkes said. "So for some of the mountain valleys, (temperatures) will be near freezing, but for us in Spokane County, lows will drop into the lower 40s."
'Godzilla-level' El Niño
Fewkes said the Climate Prediction Center, which operates under the National Oceanic and Atmospheric Administration, is predicting that temperatures are "leaning slightly warmer than normal" for the first couple weeks of October.
"Typically with El Niño for our area, precipitation amounts are right around normal, but the temperatures are warmer," Fewkes said. "On average, it manifests itself as less snow. But that's not certain. It varies a lot year to year."
She said currently all the long-range forecasts are leaning toward above-normal temperatures, but "the forecast really kind of loses scale" as it goes farther out. Their forecasting ability diminishes past 10 days out.
El Niño is described by the United States Geological Service as a warming of the ocean surface, or above-average sea surface temperatures, in the central and eastern tropical Pacific Ocean.
El Niño events recur irregularly, the website explained, from every two years to every decade.
Notably, no two events are the same.
Recent data from the Climate Change Institute at the University of Maine revealed that the sea surface temperature in the heart of El Niño has now hit 37.49 degrees Fahrenheit, which beats the previous high of 37.436 degrees set in November 2015.
That means this year's El Niño is officially the strongest ocean anomaly in the last 170 years.
A "super El Niño" typically peaks between November and January. The most recent forecasts predict a peak of 39.2 degrees Fahrenheit in November and December. Zeke Hausfather, a climate scientist with Berkeley Earth, used the average of 14 different models to reach this conclusion.
If this estimate is correct, it makes this year's El Niño far ahead of any previous event. Hausfather referred to it as "mind-blowing," while other climate scientists have referred to it as a "Godzilla-level" phenomenon.
Any temperature increase above 32.9 degrees Fahrenheit is considered an "El Niño" event, while anything above 35.6 degrees is categorized as a "super El Niño." This year's El Niño has already beaten the previous record, with months still left before the ocean event reaches its peak.
This event, coupled with human-induced global heating, means that 2027 looks certain to become the hottest year on record. Year after year, climate scientists have watched as the newest year replaces the previous year as the hottest on record. It appears to be a trend that won't slow down anytime soon.
While an accurate prediction for summer 2027 is that it's going to be really, really hot, what about this winter? That question, according to Paul Loikith, a climate scientist at Portland State University, is a little harder to answer.
"There's a lot of variability in the Pacific Northwest when it comes to how we are affected by El Niño and La Niña in general," Loikith said. "When you have a very strong El Niño event like this, things don't necessarily behave the same way that they do with the more average-type events. So that just throws another piece of variability and uncertainty into making confident forecasts."
With only a handful of "super El Niño's" to look back on, Loikith said they've "all had somewhat different winters." And because the Pacific Ocean undergoes numerous oscillations that can modulate the impacts of a super El Niño, it becomes really difficult to predict what this winter has in store for the Pacific Northwest.
Using the Climate Prediction Center, Loikith said all of the Northwest has a "small or slightly above-equal chance of being warmer than average." In other words, it's not a high probability that this winter will be warmer than usual, but the likelihood is slightly above 50%.
"For most of the Northwest, except for coastal Washington, it has equal chances of being wetter or drier than average," Loikith said. "So it's not a really strong signal from the experts there in that time frame."
In this context, equal chance means it's 50-50 whether it's going to be warmer or cooler than normal. If something is "slightly above" equal chance, that means it's a small percentage above 50%.
Loikith said it's leaning toward drier than average for the Inland Northwest between October to December.
"It's also important to remember it's not telling you about the weather," Loikith said. "It's telling about the three-month average. So it's possible that in that warm stretch, you still get a cold snowstorm. So it's really not telling us much about individual storms."
Predicting how an El Niño event will manifest itself is always tricky, he said, but in a super El Niño event, it's "even trickier."
"In the 2015-16 Super El Niño, the expectation, based on the '97-'98 El Niño, is that Southern California would be really wet," Loikith said. "We got into midwinter and it was still really dry. And by that point, it was clear that prediction was not coming true. And in fact, here in the Northwest, we were really wet that year. So as you're getting into the core of the winter season, we'll see how it's unfolding, but that doesn't give a ton of lead time."
In the more immediate future, warmer days are expected to get fewer and further between as sunlight hours decrease. As for what the rest of the winter will look like in the Inland Northwest, the best thing to do is to wait and see.
"It's harder than I think we want it to be sometimes to make these definitive forecasts," Loikith said. "Just because the El Niño is super strong, does not necessarily mean that the impacts will necessarily follow that same sort of strength. The atmosphere could respond in different ways, and so time will tell how it all pans out."
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