After a warm and dry November, southwest Wyoming may start to see more “Christmasy” weather with colder temperatures and more chances for precipitation this month.
Thursday and Friday are expected to bring the first major snow we’ve seen this winter, with the exception of the storm Oct. 12. Since then, Southwest Wyoming hasn’t seen any meaningful snowfall until now.
The National Weather Service issued a Hazardous Weather Outlook on Tuesday, warning of probable snow in the mountains that night, strong winds from Rock Springs to Casper, and potential snow the rest of the week, especially Thursday and Friday.
On Wednesday, the National Weather Service added a Winter Weather Advisory, which will extend from 5 a.m. Thursday to 5 a.m. Friday. The advisory predicts 3 to 6 inches of snow, with the highest amounts south of Interstate 80. Wind gusts could be as high as 35 miles per hour.
While snow isn’t in the forecast after Friday, cold temperatures are. Saturday night’s low is expected to be around 11 degrees.
This weather is typical for Wyoming during the holiday season, but a contrast to the high temperatures and lack of precipitation the state saw during November.
According to Trevor Lavoie, a meteorologist from the US National Weather Service office in Riverton, average temperatures across Wyoming in November were well above normal, and several locations set record high temperatures. Most places throughout the state, including Green River, also saw a lack of precipitation.
Much of the strangely warm and dry weather in November was due to a La Niña pattern.
“We went into a La Niña pattern last winter, which pretty much set the tone for how dry it was, and we’re in a La Niña pattern again this winter,” Lavoie explained.
La Niña and El Niño are climate patterns that refer to changes in conditions with typical temperatures and trade winds over the Pacific Ocean. During a La Niña pattern, ocean surface temperatures cool and trade winds blow stronger, pushing a jet stream across North America. This tends to lead to drought conditions in the south and wetter, colder weather in the north.
The La Niña jet stream represented on some maps and diagrams goes right over Wyoming, leaving it in both dry and cold regions.
Thinking of last winter’s weather and how it may predict what we can expect this year, Lavoie pointed out January and February were drier, while the late winter and early spring brought more precipitation and heavier snow, like the storm that hit Cheyenne in March. Lavoie also said this year’s La Niña pattern is stronger than last year’s event.
“It’s a moderate La Niña, so that may make it even drier. But there’s also some other oscillations that come into play each winter so it may not be an exact repeat of last year,” he said.
For this month, however, chances for snow are up. Lavoie said Western Wyoming, particularly the northwest portion of the state, has above normal chances for precipitation, and everywhere else has equal chances. Temperatures in December should be closer to normal for Wyoming, which means it should be colder than November’s unusual highs.
“Hopefully this month we’ll start seeing a more active pattern so we can get some more snow on the mountains,” Lavoie said.
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