The dance of this Fort Collins winter would be an easy one to master: Mild, unseasonable warmth, followed by a burst of cold and maybe a dash of snow. Repeat.
It's been a winter replete withwarm, coat-shedding days andlight snows that vanish quickly from the ground. High temperatures have reached 55 degrees or warmer about one-third of days since Dec. 1.
But we're not far behind the normal snowfall total for this point in the season, and about one in seven days have left us home-bound and shiveringwith highs below freezing.
There's a name for this seasonal dance: La Nina in Northern Colorado.
The region is seeing the true colors of a weak-to-moderate La Nina, or the cooling of waters near the Equatorial Pacific. Savvy weather-watchers might remember last winter was also a La Nina winter, which is why this year feels a lot like last year.
La Nina is also the primary culprit of achingly low snowpack in southern Colorado and below-normal snowpack in Northern Colorado, meteorologists say.
It's not unusual to see big oscillations in Northern Colorado winter weather, said National Weather Service meteorologist Mike Baker. But La Nina years have a special reputation forinconsistent temperatures, he added.
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"We can get big blasts of cold air, but they don't hang around very long, and then we get these big surges of warm air,"he said. "If you want to assign an adjective to a La Nina pattern from the mountains eastward, it would be 'highly variable.'"
In aLa Nina winter, the mountains often usher in cold, shallow masses of air from the northwest, Baker said. Those weak cold fronts bring us light snows or freezing drizzle paired with chilly temperatures.
But after a day or two, warm, dry winter winds called "Chinook winds" rush down the east slopeand flush out the cold air. Baker compared it to ocean waves rolling in and out of a shoreline.
This pattern happens during non-La Nina winters, too — just not as often, Baker said.
Still, Fort Collins scrounged up 17.6 inches of snow between Dec. 1 and Feb. 8, just below the normal amount of 18 inches. Meteorologists use 1981-2010 normals from the Fort Collins weather station at Colorado State University to compare daily weather to average conditions. Most of that snow came from storms that dropped less than 3 inches — the only heavier storms were on Jan. 21, when the Fort Collins weather station logged 3.9 inches, and Feb. 1, with 4.4 inches.
Compare that to the first three months of winter 2015-16, when our two heaviest storms dropped 7.4 inches and 7.8 inches. That was an El Nino year with lots of heavy, upslope snow storms.
ButMarch, historically the snowiest month of the year, is yet upon us. April brings an average of 6.2 inches of flakes, too. So the snow show isfar from over.
Projections from the National Weather Service's Climate Prediction Center indicate recent warmth is likely to persist in Northern Colorado. So far this winter, average temperatures have lingered about 2.5 to 3.5 degrees warmerthan normal. On a big-picture scale, this follows a general warming trend that experts say is due to climate change. But the link between La Nina, El Nino and climate change needs to be researched further, according to the World Meteorological Organization.
La Nina is a driving factor for the low Colorado snowpack that is worrying water experts,Bakersaid. Mountains in north and north-central Colorado tend to fare better than the southern mountains during La Nina winters, Baker said, because the storm track is typically oriented from northwest to southwest.
"Storms come in from the Pacific Northwest, and they impact mountains in north and north-central Colorado," Baker said. "The flow is just not very favorable for development of snow in the southern mountains."
Many snowpack monitoring sites are seeing record-low snowpack, especially in the Sangre de Cristoand San Juan mountains, Colorado state climatologist Russ Schumacher said.
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The Arkansas and Gunnison basins are at their lowest snowpack on record, at 56 percent and 49 percent of the normals for this time of year, respectively. The Upper Rio Grande andcombined San Miguel, Dolores, Animas andSan Juan basins are at their second-lowestlevels on record, Schumacher said, citing data from the Natural Resources Conservation Service.
That snowpack data only goes back 35 to 40 years, Schumacher noted, so it's impossible to directly compare today's snowpack to levels during Colorado's historic 1976-77 drought.
"...but I think it’s fair to say that in many spots, this winter is just as bad if not worse as that one," Schumacher wrote in an email. "In the two southwest basins, there’s never been a year with enough snow from this point forward to get us back to normal, so we’ve been saying that there’s effectively no chance of getting to normal in those parts of the state."
Conditions look better in the South Platte and Upper Colorado river basins that feed Northern Colorado water supply. The South Platte basin sat at 93 percent of normal on Thursday, the best in the state. The Upper Colorado basin sat at 79 percent of normal.
Both basins could get back to normal if late winter and spring bring healthy snowfall, said Schumacher and Northern Water spokesman Brian Werner.
Werner noted regional water storage is 24 percent above average thanks to wet seasons in years past.
"We try not to get too confident or too panicked," he said. "We're a little over halfway through the snowpack accumulation season. We've seen years go south on us from here out, and we've seen years turn around with wet spring storms."
Winter 2017-18 in Fort Collins
December
Average maximum temperature:47.2 degrees
1981-2010 normal: 42.8 degrees
Average low temperature: 20.3 degrees
1981-2010 normal:17.7 degrees
Snow: 7.2 inches
1981-2010 normal: 8.4 inches
January
Average maximum temperature: 48.1 degrees
1981-2010 normal:44.2 degrees
Average low temperature: 19.8 degrees
1981-2010 normal:17.9 degrees
Snow: 6 inches
1981-2010 normal:7.9 inches
February (through Feb. 7)
Average maximum temperature:48.6 degrees
1981-2010 normal:44.6 degrees
Average low temperature:20 degrees
1981-2010 normal:19 degrees
Snow: 4.4 inches
1981-2010 normal:1.7 inches
