Friday, January 4, 2008

Forecasters predict major winter storm

Two to 5 feet of snow could fall in the Sawtooths and surrounding ranges

Express Staff Writer

A major winter storm that the National Weather Service is forecasting to arrive in the region by today could drop as much as several feet of snow in the high country, including the Boulder Mountains, shown here looking east from Billy?s Bridge about 20 miles northwest of Ketchum. Photo by David N. Seelig

Break out your tire chains, snow shovel and your best snow dance—the big one is coming.

A warm, heavily moisture-laden Pacific storm bearing down on the mountains of Central Idaho from the southwest will likely dump as much as several feet of snow in upper elevations of the region by Sunday, forecasters with the National Weather Service in Pocatello said Thursday. The storm was forecast to arrive by 5 a.m. today.

Further to the north in the Sawtooth Mountains and surrounding ranges, the storm could drop between 2 to 5 feet of snow, different forecasting models used by the NWS separately reported.

Commenting on the two models, Jeff Hedges, NWS lead forecaster in Pocatello, said he generally favors the more conservative of the two, which takes a global view when forecasting weather systems.

Nevertheless, Hedges said even the more conservative model was forecasting at least 2 feet of snow by Sunday for the mountains.

"It's going to be a pretty considerable storm. The mountains are definitely going to get hammered," he said.

Hedges said the other forecasting model the NWS uses is occasionally prone to exaggerating precipitation amounts.

But snow lovers take heart. Hedges said it's not entirely out of the realm of possibility that the more substantial amounts forecast for the region by Sunday could come to pass.

"If it ended up being 3 to 4 feet up there I wouldn't be totally surprised," he said.

Hedges said snowfall somewhere in the middle of the two forecasts is probably more likely.

He said the type of weather system shaping up typically gives Idaho's south-central mountains their greatest snowfall amounts.

Hedges said that sometime on Friday, the winds will shift and begin blowing directly from out of the south. He said that weather scenario blows over the sagebrush steppe of the Snake River Plain, picking up moisture as it starts going upslope into the mountains of Central Idaho.

"That brings moist air into you guys," he said.

Speaking by phone around noon on Thursday, Hedges said he expected to change an existing winter storm watch covering the Big and Little Wood River drainages and the Sawtooth Mountains to a more imminent winter storm warning sometime later in the day. A NWS winter storm warning means significant snowfall is expected.

Even in their earlier winter storm watch, forecasters were calling for a major snow event.

"Snow totals may have to be measured by the foot during the period from Friday morning to Sunday morning," the NWS advisory stated.

Down in the lower portions of the Wood River Valley in the Hailey and Bellevue areas, the warm weather system may translate into a rain-snow mix at times, the advisory went on to say.

"Expect much lower accumulations below the 5,500-foot elevation. The best chances for heavy snow should be above the 6,500-foot elevation," the NWS advisory concludes.

Hedges warned that the incoming weather system will also bring heavy winds and blowing snow at the upper elevations. He said weather systems that bring heavy snowfall but don't include high winds are typically given a heavy snow warning rather than a winter storm warning, which is a multiple-weather-event type of forecast.

Though the Sawtooth National Forest Avalanche Center's daily avalanche advisory on Thursday predicted just a moderate avalanche danger for the region, it did call for increasing avalanche danger once the incoming winter storm arrives.

In the Thursday advisory, Matt Lutz, an avalanche forecaster for the center, said that as the storm starts to impact the area the avalanche danger will likely increase rapidly.

"Friday night through Saturday is expected to see the greatest snowfall intensity," he said. "This storm is expected to be warm and windy with mountain snow totals dare I say measured in feet.

Based on his personal observations in the upper Baker Creek drainage in the Smoky Mountains northwest of Ketchum, Lutz said there was evidence of numerous surface slabs that probably naturally avalanched during last Sunday's windy storm.

"These slabs appeared to be between 12 to 16 inches deep and were primarily on southerly aspects," he said.

Lutz also said that he received a report that a snowmobiler triggered a small slab in the headwaters of the Salmon River on Wednesday.

To view the center's daily avalanche forecast, go to or call 622-8027.

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