MINNEAPOLIS (WCCO) — We know it is going to snow Wednesday. We know it is going to be heavy and wet. We even have a good idea when the storm will start.
But what is hard to pinpoint exactly is how much we will get.
So, why is hard to predict snowfall? WCCO Chief Meteorologist Chris Shaffer says it is because people “obsess” about the totals.
“Nobody cares with rain, but with snow not only do they care, they care precisely,” Shaffer said. “Two to four inches is almost too vague.”
Wednesday’s snowstorm is an especially challenging one for forecasters because of the extreme cutoff over the metro — a very populated area. Hypothetically, six inches could fall in the downtowns, a foot in Owatonna and none in Cambridge.
“If that storm shifts 30 miles, you’re a hero or a zero for forecasting that thing,” Shaffer said.
Meteorologists use a combination of five or six different computer models to forecast storms. Those models — including the European, GFS, NAM and RPM — can vary greatly because they are all interpreting different data.
“They’re all good at different things,” Shaffer said. “Some models you lean on for thunderstorms, other with snow. You pick your poison.”
The models differ by a number of different factors, like how long the snow stays as rain, where the core is centered or how fast it is expected to move. Some models are updated hourly, while others twice a day.
Each meteorologist then uses his or her past experience to interpret, favor or ignore any combination of those models. Ultimately, Shaffer says human factor plays a big role in the forecast.
“Generally, you’ll see most of that agrees, then it falls on tendencies,” he said. “Some people like to over-predict. That way if its’ less, they feel like people aren’t as mad. Others are more conservative in it because they don’t want to scare people.”
But fear not, that same human experience also allows the meteorologist to forecast more precisely how hard travel will be, how fast the wind might whip and how long it will be before the snow that does fall melts.
“When I’m talking about what will tomorrow will be like, I think there’s going to be snow, I think it’s going to be heavier south, I think it’s going to be windy, temperatures will be hanging in the 30s,” Shaffer said. “I think nine out of 10 things I told you will happen. The exact snow amount, probably not.”
Click here to read and watch Shaffer’s full forecast.