Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=111099
Story Retrieval Date: 5/24/2013 6:17:56 PM CST
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Blizzard bust shows challenges of predicting Chicago weather
by Liz Hoffman
Jan 13, 2009
NOAA National Weather Service
Chicago saw between 1 and 3 inches of snow and 20- to 25-mph winds Monday night and into Tuesday morning -- a far cry from the blizzard conditions predicted by local forecasters.
The blizzard that wasn't: Two experts weigh in
WGN's Tom Skilling and Northern Illinois University’s Gilbert Sebenste break down what happened to the blizzard predicted for Monday night. The “bust” – a blown forecast, in meteorologists’ lingo – was the result of a trio of weather anomalies. “One of these, no problem – the blizzard hits and we’re still right,” Sebenste said. “It was a perfect storm of things going wrong.”
1. Wind: Gusts that clocked in as high as 75 mph in Rapid City, S.D. on Monday morning died down drastically when they moved east. Instead of the 35 mph gusts predicted, Chicago only saw 20- to 25-mph winds. “You know [the wind] is going to slow down, but predicting exactly how much and when is hard,” WGN meteorologist Tom Skilling said.
2. Rain: Snowflakes have to form around something – usually a piece of dust or dirt in the air. But the air over Chicago Monday night was so clean, Sebenste said, that the moisture fell as freezing rain between 8 and 11 p.m. This formed an ice crust on top of the snow, which kept the snow from blowing and drifting. This weather phenomenon, known as “super-cooled water droplets,” is extremely rare.
3. Snow: The storm system came through faster than expected and instead of dropping 3 to 5 inches, most of the northern part of the state saw only 1 to 3. “The storm tracked a little north and it turned out not to be the system we anticipated,” Skilling said.
It wasn’t.
And as he lay in bed in his too-quiet home, Changnon, a meteorology professor at Northern Illinois University, knew he’d be waking up to a flurry of complaints. But such is the life of a meteorologist – part science, part art, part luck.
“It’s kind of a lonely profession that way,” said Changnon.
Or as WGN meteorologist Tom Skilling put it: “People watch the weather closely, and they let you hear about it when you’re wrong.”
The National Weather Service issued a blizzard warning for northeastern Illinois, which local TV forecasters echoed in their evening broadcasts. Chicagoans went to bed expecting 3 to 5 inches of snow, 35-mph wind gusts and whiteout conditions.
But they got just 1 to 3 inches of snow and 20- to 25-mph winds, according to National Weather Service’s Romeoville office. Midway Airport recorded 3.4 inches, the most in the five-county Chicago area, as the storm moved quickly through northern Illinois. The National Weather Service cancelled the blizzard warning at about 4 a.m.
This kind of “bust” – meteorologists’ lingo for a blown forecast – is sometimes unavoidable in a Chicago winter, but still left some area forecasters scratching their heads.
“It just reminds you that for all our technology and all our gadgets and all our expertise, we are not 100 percent,” said Gilbert Sebenste, Northern Illinois University’s staff meteorologist.
Sebenste said forecasters are usually cautious when deciding to issue warnings, to avoid unnecessary panic. But storms like Monday night’s – fast-moving and intense – are especially hard to nail down, he said.
“We walk a fine line and we do the best we can, but in these types of situations, often you’re darned if you do and darned if you don’t,” he said.
While technology has made forecasting more accurate than ever before, winter weather is particularly tricky. WGN meteorologist Jim Ramsey says he tries to make his forecasts as accurate as possible, but know he won't hit the mark every time.
“Can I be good enough, often enough that I’m useful?” Ramsey said. “I always want to nail it, but that’s what I aim for.”
And as Sebenste pointed out, the best part about a Chicago winter is that there’s always another chance to get it right. The forecast for Tuesday night and into Wednesday calls for 2 to 5 inches of snow and temperatures in single digits with bitterly cold wind chills.
“I guess we’ll see,” Sebenste said. “I might still have a job in the morning.”
