Science explains underwhelming snowstorm

Friday, December 30, 2016 - 13:23
Forecaster says warm layer of air likely culprit for lower-than-expected totals
  • Snow on a gas meter shows how much snow fell in Eagle River during the Thursday, Dec. 29 snow storm. Forecasters expected as much as half a foot to fall in Eagle River, which instead got two or three inches.

Southcentral Alaska will have to wait until at least 2017 for its storm of the century.

On Thursday, forecasters predicted half a foot of snow would fall in the Anchorage and Eagle River areas, with a foot or more dumping on the Mat-Su. Office workers were encouraged to leave work early to avoid the rush hour carnage that was expected.

“The largest snowfall in several years is possible for portions of the Matanuska Valley” north of Anchorage, wrote the National Weather Service in a public bulletin about the storm.
Didn’t happen.

Rather than a massive “snow event,” the area was instead dusted with a respectable – but far from life-altering – two to three inches, with as much a six or seven inches falling at higher elevations such as Hatcher Pass in the Mat-Su. The reason? Science.

“We were just talking about that,” said National Weather Service forecaster Shaun Baines on Friday morning.

Baines and his colleagues were discussing why the predicted snow arrived with a whimper instead of a wintry wham.

“One of the things we do as forecasters is forecast how much liquid is going to fall,” he said.

The forecast office figured the wet, heavy clouds lumbering toward Anchorage and the Mat-Su were full of liquid that would turn into a foot or more of light, fluffy snow. He explained that a tenth of an inch of liquid that produces one inch of snow has a 10-to-1 ratio. A higher ratio means fluffier snow.

“We probably average between 15- and 25-to-1,” he said.

Based on the office’s models, the snow was expected to be somewhere in that range. Instead, it was more like 5- or 10-to-1.

Bottom line: The snow had a higher moisture content than expected, meaning less of it piled up on the ground.

“We were expecting really dry snow and it was really wet,” he said.

The office’s moisture predictions weren’t that far off, he said. The Ted Stevens International Airport – which typically gets the least snow in the Anchorage Bowl – received about four-tenths of an inch of water.

“In many cases, that’ll give you six to eight inches,” of snow, he said.

Instead, only about two inches of snow had to be cleared off the airport’s 62 miles of runways – child’s play for the airport’s award-winning, 109-person airfield maintenance staff.

Baines speculated an unexpected layer of warm air somewhere in the atmosphere was the culprit for warming the precipitation. The result was snow totals that turned out to be about half as much as predicted.

“It was pretty much less everywhere, and that ratio thing was one of the biggest contributors,” he said.

Baines said he and his fellow forecasters can use the event to increase the accuracy of future forecasts by digging into the data and discussing what the office got right – and wrong.

“We regularly do that, especially with these big events,” he said.

Baines said anyone hoping for another blast of snow will likely have to wait. As he spoke, he said an area of high pressure was descending on the area and was likely to bring dry, sunny conditions for a week.

“We’re looking pretty dry,” he said.

Despite being less than forecast, the snow did give the area another much-needed boost. After three consecutive winters of rainy, dry weather, this year's respectable snowfall totals have been welcome news for outdoor enthusiasts. The area's ski trails are in excellent shape, and the dog mushing trails at Beach Lake are now covered enough for sprint mushers to set their snow hooks.

"This is definitely better than last year, I can tell you that," said Chugiak Dog Mushers Association vice president Kourosh Partow.

The lower than expected snow totals from the storm may have been a bit disappointing to skiers and snowmachiners, but the pre-holiday weekend hype combined with less snow made for better than expected driving conditions for commuters. According to Anchorage Police Department public information officer Renee Oistad, as of 10 a.m. Friday there had been just 19 vehicle in distress calls over the previous 24-hour period, one crash and zero injury accidents. A Friday drive between Anchorage and Eagle River revealed no fresh ditch-divers along the Glenn Highway between the Eastside of Anchorage and Birchwood Loop.

Oistad speculated people decided to start the New Year holiday early by staying off the roads.

“Honestly, it’s just lovely,” she said. “It’s a holiday weekend, people are staying home...and that’s a good thing.”

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