Meteorologists blame the unpredictability of snow bands and shelter from the Olympics for their off-the-mark forecasts for snow in Seattle this week.
In case you didn’t notice, this week’s forecast for snow in Seattle was off.
For those who changed travel plans or stayed home from work and are now cursing the meteorologists, here’s a look at why we’re the city that cried snow.
Part of the answer lies in the Olympics. Bands of precipitation set up north and south of Seattle on Wednesday, but for a period of time the Olympics sheltered the city from the precipitation, according to National Weather Service meteorologist Carl Cerniglia.
Air came from the west on Wednesday over the mountains, and it warmed as it sank down the mountains, University of Washington meteorologist Cliff Mass said. Warm air can hold more water vapor than cold air, which meant less precipitation over Seattle.
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Though Mass said it was clear that this would happen, it was uncertain where bands of snow would set up. He said one weather model at 4 p.m. Tuesday — just in time for 5 p.m. news broadcasts — suggested a band would set up over Seattle. But then the next morning models showed the band pushed up north.
That’s just the nature of snow bands, Weather Service meteorologist Danny Mercer said. They typically float around, leading to hit-and-miss snow.
Even so, Cerniglia said, all the models the weather service used to predict snowfall had forecast “quite a bit of snow — 6 to 8 inches over downtown.” The weather service even cut back from extreme models to be cautious, predicting about 2 to 6 inches in Seattle.
And they weren’t the only ones calling for snow: Mass predicted in a Tuesday blog post that 1 to 3 inches would fall in South Seattle and 2 to 5 inches in North Seattle.
“It just didn’t work out that way,” Cerniglia said. “It’s just the way the system evolved. It just didn’t pan out that the snow fell in the central Sound.”
Weather-service meteorologists make forecasts from a mixture of data, including observational data and satellite radar, Cerniglia said. They combine that with information from a wide variety of model forecasts, each of which uses different equations to simulate the atmosphere. Then, Cerniglia said, they take what they’ve learned from school and professional experience to analyze all the information and put together a forecast.
But Seattle’s forecast is consistently tricky to nail down, Cerniglia said, due to its unique terrain, which influences air-flow patterns and how weather systems move. Also, all the water around Seattle impacts the snow level. Sometimes snow levels are low enough to hit Seattle, but by the time the flakes get to sea level, warmer air ends up melting them.
Still, Mercer, Cerniglia and Mass noted that the rest of Western Washington’s forecast was pretty dead on: Seattle was virtually surrounded by snow Wednesday.
“The place that was not impacted just happens to be where the majority of people live,” Cerniglia said.
And he’s not too worried if those Seattleites are upset about the off-the-mark forecast: “Doctors aren’t always right either,” he said, “but people still go to the doctors.”
Olivia Bobrowsky: 206-464-3195 or email@example.com