Powder piles up | SummitDaily.com

Powder piles up

BOB BERWYN
summit daily news

Summit Daily/ Adrian DiUbaldo

SUMMIT COUNTY – Forget El Nino. Who needs La Nina?

Without any obvious large-scale patterns influencing the weather, Colorado seems to have returned to a normal winter storm pattern, with wave after wave of Pacific moisture rolling onshore and delivering a steady series of dumps across the Northern Rockies.

“The westerlies across the Pacific are strong now and are driving repeated storms into the western mountains. It has not, however, been far enough south to produce snow and rain for the southwest USA, including southwest Colorado,” said state climatologist Dr. Roger Pielke.

Thursday’s storm snarled holiday traffic but also delivered a fresh blast of new snow at all local areas, with 6 inches at Copper Mountain, five at A-Basin, 3 at Breckenridge and 2 inches at Keystone, as of the 2 p.m. Colorado Ski Country USA snow report.

Just across the Divide, Loveland picked up 9 inches for the highest storm total of the day.

Although Breckenridge weather watcher Rick Bly hasn’t compiled the month-end totals for Breckenridge, December is sure to wind up as the third month in a row with above-average precipitation, the first time that’s happened in quite some time. As of Thursday morning, snowfall for the month was about 40 percent above average, Bly said.

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And there’s more snow on the way, with the forecast calling for waves of moisture to roll in every few days, at least through early next week.

“It’s a very progressive, active Pacific Ocean,” said Colorado Avalanche Information Center forecaster Scott Toepfer, indicating that another storm is due Saturday night, with another system ringing in the New Year with fresh powder Monday night into Tuesday.

Toepfer said it looks like the jet stream could drop a little further south with that system, bringing heavier snows to the Northern Mountains along with a good blast for the San Juans, where precipitation has been lagging a little bit. The snowpack at Red Mountain Pass is at about 84 percent of normal, Toepfer said.

In general, the southern mountains have been drier than average this season, especially compared with the past few years.

“It’s just the luck of the draw where the storm track decided to stroll this year,” Toepfer said, explaining that the jet stream has just stayed that tad to the north, which means the San Juans haven’t seen those juicy southwest flows coming in from Southern California.

The recent series of storms has been originating in the central Pacific rather than the Gulf of Alaska, which means the temperatures have been slightly warmer than average for this time of year. Looking at large-scale satellite images, Toepfer said there’s a zonal flow beginning in China and Russia and extending all the way across the Pacific before ridging and troughing as it hits the West Coast.

“In that kind of flow, the storms move in fast and move out fast, and there’s not a lot of time for dry slots to form in between,” he said. The current weather pattern comes close, but doesn’t quite meet the definition of a Pineapple Express, when copious subtropical moisture from near Hawaii hooks up with the Polar jet stream for what can be exceptionally heavy snows.

But should the present pattern shift just a little, with storms coming in slightly colder, conditions could resemble the winter of 1983, “when we were tunneling down Main Street (in Breckenridge) to get our mail,” Toepfer said.

The outlook for the rest of the winter is uncertain.

“There is very little forecast skill with a non-El Nino/non-La Nina such as we are in now. There is a tendency for weather patterns to repeat, which suggests we might see more very cold weather in the eastern USA,” said Pielke. “A repeat of the very cold weather Colorado had earlier in December is not likely in the near term, however, since large arctic air masses are not building yet in northern Canada,” he added.

While the snow is always welcome in the High Country, it makes for tricky driving conditions. Vail Pass eastbound was closed for a time Thursday morning, as was Loveland Pass, and heavy traffic stacked up on Interstate 70 east of the Eisenhower Tunnel, as skiers and snowboarders thronged their way toward the powder. Chain restrictions were in effect on many mountain roads throughout the day.

Avalanche forecasters stepped up the hazard rating for the northern and central mountains after observers reported shallow slab avalanches releasing easily in response to ski cuts, especially on steeper convex slopes, according to a CAIC hotline update. The danger near and above treeline on north to east to south-facing slopes is “considerable” with pockets of “high” on steeper slopes.

Triggered avalanches are possible to probable on many backcountry slopes.

Check in with the avalanche center at (970) 668-0600 or on the web (http://geosurvey.state.co.us/avalanche) before heading to the backcountry.