September Was Hottest, Driest In Decades, But Wyoming Can Still Expect A Cold Winter

If anyone thought September was hotter and drier than it has been in decades, they’re right. It has been in parts of Wyoming. That hasn’t altered long-term forecasts for the Cowboy State, which say people should expect a colder than normal winter.

The National Weather Service Office in Riverton reports a region-wide trend of above-average temperatures and below-average precipitation throughout western and central Wyoming in September.

Temperatures were between 3 and 7 degrees warmer than average, while precipitation was between 10% and 50% lower than average. Riverton might have gotten the worst of it, averaging 5 degrees warmer while getting only 0.08 inches of precipitation, less than 10% of their normal amount.

It was even warmer and drier in northeastern Wyoming, according to meteorologist Aaron Woodward with the NWS Rapid City office.

“Newcastle got 0.44 inches of precipitation in September, and its average is 1.2 inches,” he said. “Its mean temperature for September is 62 degrees. Last month, it was 70.5. That’s a new record.”

Woodward said Gillette’s average precipitation is 1.25 inches, but it only got 0.18 inches last month, while the average temperature there was 85 degrees, more than 10 degrees warmer than the city’s 30-year average.

Those are the hard numbers behind a simmering September in the Cowboy State. Several communities got close to breaking record highs at the end of the month while wildfires burned out of control in some dry, parched areas.

It’s all part of the plan. Or, at least, it’s part of the observable patterns that will determine Wyoming’s weather for the next few months.

“It was certainly a very warm September just about everywhere in Wyoming,” said Cowboy State Daily meteorologist Don Day. “The numbers were higher or lower than we might have anticipated, but this was pretty much the September that we were going to get.”

Warmer And Drier

According to the NWS Riverton office, Buffalo and Greybull experienced the warmest September since 1998. On average, Buffalo's temperature was 7 degrees above average, and Greybull's 4.5 degrees above.

Meanwhile, Greybull got 0.38 inches of precipitation in September, only 45% of its monthly average. Buffalo got 0.18 inches, just 15% of its average.

It was the third warmest September in Lander since 1892, in Riverton since 1996, and in Rock Springs since 1948

None of these numbers surprise Day. Nor does it have him rethinking his extended forecast of a colder, snowier winter ahead for Wyoming.

His long-range forecast for the upcoming winter anticipated a warmer and drier-than-average fall.

“Fall was going to be off to a warm, dry start and that's certainly the case,” he said. “It’s going to continue through another 10 days or so into the middle part of October before things change. So, September was expected. This is nothing that's off the rails.”

Day also noted that while it was warmer and drier, the average temperatures throughout Wyoming weren’t shockingly high. Despite experiencing its warmest September since 1998, the average temperatures in Buffalo and Greybull were 66.8 and 65.4 degrees, respectively.

When you look at those graphics, that's compared to a 30-year record of high and low temperatures,” he said. “It was really warm in northeastern Wyoming, relative to the 30-year average, but that doesn't mean Greybull and Worland weren't hot. Their average temperatures were above average, but not as much, so it's also relative to the location.”

Where It’s Warmest

The NWS Riverton’s September summary includes a lot of “the usual suspects” when it comes to Wyoming’s warmest places, Day said. Hot air may rise in a house, but he said it usually descends into the lowest regions of the Cowboy State.

“The warmest parts of Wyoming are the lowest elevations,” he said. “If you were to look at the warmest places in Wyoming, if there is such a thing. It’d be the Bighorn Basin and places like Torrington, which is lower in elevation near the Nebraska border.

“Those lower elevation locations are going to be ‘the warmest,’ and for good reason. Other parts of the state that are higher in elevation will be a little bit cooler naturally.”

Day said there’s been an observable trend of above-average temperatures since the beginning of the year, but primarily in eastern and northeastern Wyoming. Otherwise, it’s been a fairly average year temperature-wise.

“Those eastern and northeastern counties have been the warmest for the whole year relative to average,” he said. “The temperatures up till September across the state weren't anything off-normal, so to speak.

“But the heat in September certainly skewed those average temperatures for the year, especially in the eastern counties. That’s where it's driest, so that's what you'd expect.”


What About Winter?

With above-average temperatures in September, some might see a persistent trend that could doom Wyoming’s winter, keeping it warm when it should get and stay cold.

Day predicted a colder, snowier winter in the 2024-2025 winter season. His outlook has not changed because the main factor that gave Wyoming a warmer September — La Niña — is on track to deliver a colder winter.

“We talk about La Niña and El Niño a lot,” he said. “When we're in these La Niña patterns, we tend to have a warm, dry start to fall. So, it's no surprise that we're in a La Niña pattern, and we’ve had a warm, dry September. We’ve seen this before.”

Based on historical analysis and computer models, Day anticipates the strengthening La Niña will bring colder-than-average temperatures across Wyoming, which will persist into the first weeks of spring. There could also be several sub-zero outbreaks, like the ones that brought minus 50-degree windchills to many Wyoming communities in January.

Meanwhile, Winter 2024-2025 should also have above-average snowfall, but certain areas should be more impacted than others. While last winter seemed to disproportionately drop more snow in the southern half of Wyoming, Day believes this winter will be more advantageous for the snowpack in northern Wyoming.

Day stands by his long-range winter forecast. Wyomingites should enjoy the warmer days because they’ll probably crave it in a few weeks.

“A warm fall doesn't mean a warm winter,” Day said. “We still expect things to turn at the end of this month and into early November. It was certainly warmer in September, but that’s what you’d expect.”

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