Last week, Southwest Colorado saw enough snow to cancel school and snarl travel. A week later, winter appears to have vaporized – replaced by clear skies, dry roads and temperatures warm enough for sandals and T-shirts.
According to the National Weather Service, high temperatures in Durango reached 63 degrees Thursday. It is the latest episode of weird winter weather this year.
Jonathan Harvey, an associate professor of geosciences at Fort Lewis College, said in an email to The Durango Herald that winter’s absence is because of stubborn high-pressure ridges steering the jet stream – a belt of fast-moving winds that separates warm tropical air to the south from cold arctic air to the north – toward the northern United States.
“We have spent most of the winter under a ‘ridge’ in the jet stream, which has prevented cold air and storms from hitting our region,” he said.
That, according to National Weather Service forecaster Lucas Boyer, is because of warm seawater temperatures in the Eastern Pacific Ocean.
“We’ve had ample warm water in the in the Eastern Pacific for a lot of the winter,” he said. “We’ve really seen the jet stream get pushed north, which means warm air to the south. It’s been really devastating for any kind of snowfall production.”
Boyer said any storms that have managed to break through that high-pressure ridge were followed by periods of temperatures 10 to 15 degrees above the historical average.
The storm that materialized last week resulted from a breakdown of that ridge, allowing enough arctic air and a series of fast-moving winter storms to make their way to the Southern Rocky Mountains, Harvey said.
“We went from near-record highs for most of February to more seasonally appropriate temperatures as those storms came through,” he said. “Unfortunately, the ridge re-formed rather quickly afterward. With the higher sun angles of February and plenty of warmer-than-normal air still present south of the jet stream, we got right back up to high temperatures again.”
The sudden oscillation from cold and snowy to warm and sunny is more common at this point in the season as the planet gradually begins to shift from winter to spring, Harvey said.
Additionally, Boyer said above-average temperatures are expected to persist as winter comes to an end.
“Our highs for the next week are pretty much holding 10 to 15 degrees over normal,” he said. “I’d say we have a 40% to 60% chance of above-average temperatures heading into May.”
The warm, dry winter has hurt snowpack in the San Juan Mountains. Boyer said the water equivalent in the San Juan River Basin is at 17% of the historical median, while the snowpack in the San Juan Mountains is 40% to 50% of average.
Unfortunately, Harvey said there is not much time left for mid-elevation snowpack. But, there is still time for high-elevation snowpack.
“Higher elevations like Molas and Red Mountain Passes don’t typically reach their peak until mid- to late-April, so there is still time to bolster the high-elevation snowpack to levels that will paint a brighter (less devastating?) picture for the runoff season,” he said.
Additionally, the NWS reported Feb. 12 that temperatures in the Eastern Pacific are gradually cooling, meaning the stubborn high-pressure could break down. That could mean a more active weather pattern for Southwest Colorado.
“The current two-week forecast models show a much more dynamic jet stream, so I would expect more frequent precipitation events in the first half of March,” Harvey said. “As long-term residents know, March storms can be cold and snowy or warm and rainy, so we’ll have to see how warm or cold they come in.”
In retrospect, he said this season’s weird, warm weather is either record-setting or close to the record. In the past century, only the notoriously bad winter of 1980-81 was as warm as this year’s.
But that, he said, is mostly because of how stubborn the jet stream has been.
“Every long-term station in our region – including Grand Junction, Albuquerque, Flagstaff, Alamosa – have recorded their warmest or second warmest (winter) on record,” Harvey said. “My take is that while a warming trend to our winters is clearly visible in the long-term records, you don’t get a winter this hot and dry without having some freakishly bad luck with the jet stream.”
sedmondson@durangoherald.com
