Northwest has seen its share of dangerous storms
'Frankenstorm' not likely here, pros say
Tuesday, October 30, 2012
Striking scenes of roofs ripped off buildings, downed trees, tragic deaths and massive flooding aren't exclusive to Hurricane Sandy's East Coast path — similar storms loom large in the Pacific Northwest's not-so-distant past.
On Oct. 12, 1962, the Columbus Day Storm killed 50 people, destroyed homes, knocked down 15 billion board feet of timber and caused extensive power outages in the region. That day, three people died in Vancouver, planes at Pearson Field were tossed through the air like toys and cars were blown sideways off the freeway.
"It produced winds well over 100 mph and caused damage from San Francisco to Vancouver, B.C.," said Tyree Wilde, weather coordination meteorologist for the National Weather Service in Portland. "And it actually wasn't that much different than Sandy, in terms of strength."
The strongest winds that day were clocked at 179 mph, with 116 mph in Portland, he said.
Such storms are rare, but there's no reason to think one couldn't happen again.
The Columbus Day Storm grew from the remnants of Typhoon Freda, which traveled across the Pacific from Japan over the course of a few days.
Most typhoons lose strength and die out before they cross the Pacific. But occasionally, one makes it through, carried along the jet stream as a low-pressure system.
And sometimes, those storms can get re-energized and spun up by atmospheric forces over the ocean before they slam into the U.S. West Coast, with destructive results.
"They come in on a track from the southwest to northeast Pacific," said Nick Bond, state climatologist at the University of Washington. "Our very biggest ones tend to develop 500 to 1,000 miles off our coast."
The Columbus Day Storm didn't have a lot of moisture associated with it. There was some rain, but most of the damage was caused by wind.
That's not to say such storms couldn't pick up moisture.
"They can have a great deal of moisture associated with them," Bond said. "They can re-intensify and grow through certain conditions in the mid-Pacific."
The bigger culprit for excessive moisture and flooding, though, tends to be the Pineapple Express, a weather phenomenon that goes by the more technical title of "atmospheric river events" in the scientific world.
"What happens in that is the jet stream taps subtropical moisture around Hawaii and funnels it here," Wilde said. "It's like a fire hose aiming right at you. And it often lasts for about four days."
That's what happened during the big December 1964 to January 1965 and February 1996 floods.
In the 1996 flood, the conditions caused the Columbia River in Vancouver to crest its 16-foot flood stage and reach 27.2 feet. The event damaged 280 Clark County homes and forced 1,500 people to flee to higher ground.
The current system of rain and mild temperatures we're experiencing is an atmospheric river event, but it's not particularly strong, Bond said.
"It's kind of your standard-issue event for fall and winter around here," he said. "Still, it's a soaker."
The pattern should remain for the next week or so, then shift back to colder conditions, he said.
The severity of Pineapple Express storms increases when larger masses of warm water near Hawaii couple with faster winds blowing toward the Cascades from the southwest Pacific. Significant flooding can occur in that case.
Fortunately for people in our region, it's highly unlikely that a Columbus Day Storm-type event could combine with a Pineapple Express, Wilde said.
"It's just a different mechanism that forms them," Wilde said. "The strong low-pressure systems, like the Columbus Day Storm, they last maybe 12 to 18 hours. A Pineapple Express would last longer, at least a few days."
Snow and ice storms can also create problems in winter, and can be notoriously hard to predict, Bond said.
"Some of our biggest snow events are things coming out of the Gulf of Alaska that get phased with moisture out of the southwest," Bond said. "The boundary of those can be very hard to forecast. The snow and ice storms that happened around Olympia in January were like that."
In Vancouver, a lot of the snow events come when cold air comes down through the Columbia River Gorge and combines with moist systems, Wilde said.
For all of the systems, the fall and winter months tend to be the most active. The period from November through February is the most active for windstorms, and the period from November through March is the most active for floods and ice storms, he said.
This fall and winter, though, look like they're shaping up to be relatively mild, the two said.
"Right now we're in neutral conditions," Wilde said. "The last two years we were in La Niñas, which tend to be wetter. This winter it's looking like a very weak El Niño, which is typically a bit drier for us. But we'll still probably have a few good storms over the season."