Cooler Temps Ahead As Autumn Weather Will Finally Arrive On Oct. 18

Cowboy State Daily metereologist Don Day says Oct. 18 is the day when the jet stream will get un-stuck and bring Wyoming much cooler temperatures and maybe even some precipitation.

AR
Andrew Rossi

October 10, 20245 min read

Sun coming up over Skyline Drive in Rock Springs, Wyoming.
Sun coming up over Skyline Drive in Rock Springs, Wyoming. (Reader photo: Holly Fronk)

While wildfires are raging in Wyoming, the southern states have been decimated by back-to-back hurricanes. It’s all connected, and it’s almost over.

According to Cowboy State Daily meteorologist Don Day, we just have to get to Oct. 18.

“We are seeing signs that changes are coming,” he said. “And it’ll take that long for those changes to reach Wyoming, so it’ll be more of the same until then.”

Jet Stream’s Stuck

Day anticipated a warmer-than-average fall in his long-range forecast for Wyoming’s upcoming winter. Daytime temperatures in the latter half of September and the first weeks of October have been in the 70s and 80s, above the Cowboy State's seasonal average.

It’s also been drier-than-average this fall, with many regions of Wyoming receiving a fraction of their average rainfall in September. That’s allowed several wildfires to uncontrollably grow to immense sizes and consume thousands of acres.

Day said the primary reason Wyoming’s weather has stayed this way for so long is that the jet stream has been stuck.

“When you get into these fall patterns like this, it means the jet stream has been in a similar configuration for the last four weeks,” he said. “The pattern’s been unchanged, so we’ve been seeing the same weather.”

The “stuck” jet stream is the same explanation for the back-to-back hurricanes that ravaged the southern U.S. Hurricanes Helene and Milton formed within a week of each other because the prevailing weather patterns didn’t change between the two tropical storms.

“Getting two hurricanes so close together is another indication that those patterns aren't changing much across the Northern Hemisphere,” Day said.

Log In The Stream

Day compared the unchanging jet stream to a log that falls in a forest stream.

“When a log falls across a stream, it’s going to back up the water and keep things from moving,” he said. “You’ve got to get rid of the log for things to start moving again.”

According to Day, that phenomenon is observable on a global scale. While it’s been warmer and drier in Wyoming, it’s been persistently cold and wet in Alaska and the Northern Pacific. It’s opposite ends of the same blocked jet stream.

That’s why Day has been keeping Oct. 18 on his calendar and in his daily weather updates. That’s when he expects the jet stream to get unstuck and bring a definite change in the wind for Wyoming and the entire Northern Hemisphere.

“The change is starting today, and things are going to start noticeably changing here in another week,” he said.

The Third Week Of October

Based on Wyoming’s historical climate data, warm weather ends by the third week of October. Day said that’s when “the dam breaks” for warmer-than-average falls.

“History is on our side,” he said. “That's why I've been confident about a change around the 18th to the 20th. That tends to be a week where things change, historically.”

As days get shorter and nights longer, masses of colder air continue to build at the northern latitudes of the globe. By mid-October, the colder air reaches the critical mass for widespread change further south.

“That’s going even quicker every day,” he said. “The daylight changes more rapidly, and the colder air builds. Eventually, you can’t stop it, and fall will get here. You usually don't see it delayed past the third week of October.”

There’s another promising sign of seasonal change in the currently stuck jet stream. Day said weather models are showing “a big dip” into the Great Lakes region this weekend and early next week, bringing a cold spell to the Midwest that will reach the Western U.S. soon after.

“That’s why I've been talking about Oct. 18,” he said. “That’s how long it will take for the changes we’re seeing now to reach Wyoming and the West.”

When It Gets Here

The first signs of seasonal change are always seen in Wyoming’s mountains. Day said that’ll be the case next week when fall finally reaches the Western U.S.

“My confidence level is pretty high that there's a good chance of rain and snow in Wyoming's major mountains and much colder temperatures across the low elevations sometime between next Thursday and Saturday,” he said.

Day believes next weekend's weather will be “a (significant) mountain event.” The National Park Service and Montana Department of Transportation seem to be anticipating that event, as they announced Oct. 14 as the final day for the Beartooth Highway in 2024.

Next week’s mountain event might not be enough to bring precipitation to the lower elevations of the Cowboy State, but colder temperatures will be a welcome and noticeable change. With the severity of Wyoming’s ongoing fire season, Day said this is “the type of storm you want.”

“This is the type of storm you want to hit a fire season or certainly slow it down to a point where it's manageable,” he said. “For the lower elevations, next Friday and Saturday is when things will really change.”

Until Then ...

Day is confident that a significant seasonal change is on the horizon, but there’s still a week between then and now. Until then, it’ll be “more of the same.”

“We’re going to see a few more clouds over the next week, and maybe it’s going to be a little cooler, but there won’t be any discernible change,” he said. “I think where we are right now, on Thursday, we’ll notice some things starting to change by next Thursday. But we’re still a week away.”

Andrew Rossi can be reached at arossi@cowboystatedaily.com.

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Andrew Rossi

Features Reporter

Andrew Rossi is a features reporter for Cowboy State Daily based in northwest Wyoming. He covers everything from horrible weather and giant pumpkins to dinosaurs, astronomy, and the eccentricities of Yellowstone National Park.