INFOGRAPHIC | Windy and wet: Snoqualmie Valley’s weird weather
February 24, 2010
NEW — 6:10 a.m. Feb. 24, 2010
Twin Falls Middle School may be only two years old, but it has already retired one state and one American flag.
“They get ripped to shreds,” by the wind, Twin Falls financial secretary Katy Wada said.
There’s not much the administrators of Twin Falls, near Interstate 90’s exit 34, can do about it. It’s so windy here, all school custodian Betty Hamilton can do is keep the flags inside on blustery days.
Despite the weather, many remark on the beauty of Twin Falls surroundings. From their classroom windows, students can see the grandeur of the Cascade Mountains.
It is those mountains that cause the strong winds, said Cliff Mass, local meteorologist and professor at the University of Washington’s department of atmospheric sciences.
The Cascade Mountains are tall, but not uniformly so. Most of the mountain range is between 5,000 feet and 7,000 feet. In contrast, Stampede Gap, which includes Snoqualmie Pass, is only between 3,000 feet and 4,000 feet tall, providing a relatively low route through the mountains.
The wind looks for the easiest path through the mountains, and Stampede Gap is its answer.
“The air tends to accelerate through and down these gaps,” Mass said. “Generally, there is much higher pressure in Eastern Washington than in Western Washington, and the air tends to accelerate down the pressure gradient.”
That rushing air equates to a windy day in the Snoqualmie Valley.
The day after Christmas, winds in the Valley reached 50 mph. Less than two weeks later, on Jan. 7, winds topped 56 mph.
“That’s tropical storm strength,” said Kevin Knowles, who has taught meteorology at Mount Si High School for seven years.
Both measurements came from his students’ weather recording station on top of the high school.
Tropical storms start when winds reach between 39 and 73 mph. Wind that fast gives the Valley certain bragging rights.
The wind is not only strong, but it can also last for hours.
North Bend resident Dave Humphrey remembers a day when the winds wouldn’t stop. On a wintry day in 2007, he and his wife Penny realized strong gusts were ripping large limbs from the fir trees in their backyard.
“Within moments, these limbs began to rotate in the sky, and then were literally thrown at our house,” Dave Humphrey said. “I was convinced that windows would be smashed, and yelled at my wife to duck, as I felt we would get showered by broken glass.”
The tree limbs did hit the windows, but luckily did not break them.
“I spent the next day cleaning branches from my back yard, roof of the house and front yard,” Dave Humphrey said. “It was quite a pile.”
Though the winds can be ferocious, they can also raise temperatures in the Valley between five degrees and 10 degrees, Knowles said.
These warm winds, called Chinook winds, come from the east. When air molecules move faster, they get warmer, which explains why the winds speeding down Stampede Gap can raise temperatures.
Windstorms from the west usually have a cooling effect. Since most of these storms come from further away, they often slow down, not speed up, by the time they reach the Valley. Slow moving molecules tend to become denser and colder, and cause a drop in Snoqualmie Valley thermometers.
The Pacific Northwest is known for its misty weather, and the Snoqualmie Valley tends to be cloudier and wetter than its neighbor Seattle, to the west.
“We naturally get more” precipitation, because “we’re in the foothills,” Knowles said.
On average, Seattle has an annual rainfall of 36.2 inches, according to the city of Seattle’s Web site. In 2009, the Snoqualmie Valley got 47 inches of rain, according to measurements at Mount Si High School.
Once again, Valley residents can thank or blame the Cascade Mountains for their weather. The mountains push air up from the ground, which leads to both clouds and rain.
“As the air goes upwards, it cools and reaches condensation point, creates clouds and with enough cooling forces, precipitates to release,” Knowles said.
Once the air makes it over the mountains, it dries as it descends into Eastern Washington. In fact, the eastern half of the state gets 15 percent to 20 percent of the rainfall Western Washington sees, Knowles said.
“The main thing is mountains cause air to rise, and rising air gives you clouds and precipitation. That’s kind of an interesting local weather thing,” Mass said, adding that the mountains contribute to another interesting weather phenomena: thunder and lightning showers.
The familiar downpour of rain accompanied by lightning and thunder typically happens in spring, when warm air mixes with the cold remnants of winter.
Once again, the Cascade Mountains are involved. They force air to rise, making it unstable, Mass said.
“Convection thunderstorms occur when you have air that has relatively low stability,” he said.
Low stability is related to how much energy is needed to move air vertically.
Warm air, like a hot air balloon, rises. As it rises, it cools and condenses into clouds. But if the air continues to rise, if it is warmed by the sun or heated by a weather front in another direction, the air will continue to go up and become increasingly unstable.
“If you have a very unstable atmosphere, completely unstable, it will form higher and higher until you get a thunderstorm,” Knowles said.
Within the storm cloud, air cools and heats, creating downdrafts and updrafts. Gas molecules have the most kinetic energy — meaning they move more — liquid molecules have some and solids have the least.
As warm air cools, energy is released.
“As that’s released, then ultimately, that has to go somewhere and it goes right into the storm to power it,” Knowles said. “It’s like powering a battery.”
In spite of the weather, or maybe because of it, people like the Humphreys enjoy living in North Bend.
“I’m a Pacific Northwestener and I don’t mind the rain,” Dave Humphrey said. “I actually don’t mind thunderstorms. I think they’re kind of neat.”
The real bee in his bonnet is the wind, which he doesn’t like, even when it’s a warm wind. But he, like many others, lets it slide every time he lifts his eyes to look at Mount Si and the Cascade Mountains and takes in all of their glory.
Laura Geggel: 392-6434, ext. 221, or email@example.com.