• Weather Service starts issuing odds on snowfall one week ahead
  • Web-based tool predicts chances for snow of 2 inches or more

Snow lovers and haters in the U.S. have a new tool to measure their potential joy, or misery, this winter.

The U.S. Weather Prediction Center has begun issuing probability forecasts up to seven days in advance for “plowable snow” storms, which start at about 2 inches (5 centimeters).

“This is the very first official product, that I am aware of, to predict winter weather this far out into the future,” said Dave Novak, director of the center in College Park, Maryland.

The tool introduced Tuesday will give municipalities, retailers, airlines and anyone with an interest in snow a chance to get ready even when the sun still fills the sky and temperatures may be mild. What people will see on the WPC website is a map with blobs of different colors, corresponding to the odds that snow will fall.

The forecasts are bound to have different impacts in various parts of the country, said Paul Kocin, a forecaster at the center. In a northern city such as Boston that can have a barrage of snowstorms, people might shrug off the threat of the next plowable event.

Measuring Impact

However, for a Southern city such as Atlanta, which was crippled by snow and ice storms in 2014, a high chance of 2 inches or more on the way will be a much bigger deal, said Kocin, who together with National Weather Service Director Louis Uccellini created an impact scale to determine the severity of Northeastern winter storms, similar to ones used to rate tornadoes and hurricanes.

Three years of testing has gone into the forecasts, and this is the first time the public will get to use them, Novak said. Advances in computer forecast modeling are ultimately behind the ability of the center, part of the National Weather Service, to bring out the new web-based outlooks.

This is a first step and still an experimental one. Right now, the center won’t be predicting the odds for huge blizzards and run-of-the mill flurries, Novak said.

Not Absolute

Also, these forecasts are probabilistic, meaning they will reflect only the odds an event will happen, not make an absolute prediction that an outcome is inevitable. Forecasters use deterministic forecasts when they tell you it’s going to rain tomorrow.

“The public does understand odds and probabilities -- think about baseball and other sporting events,” Novak said. He used the example of a baseball player’s batting average: It’s just a prediction of how well he will do.

While some commercial vendors will predict snowfall totals more than a week in advance, the science of forecasting is limited. That means those outlooks aren’t meaningful and border on being “irresponsible,” Kocin said.

A variety of other government weather agencies already use probabilistic forecasts. For instance, the U.S. Climate Prediction Center said the odds are high the winter will be mild across the northern U.S. because of the El Nino holding sway across the Pacific.

If you live in a place such as Boston that got a record amount of snow last year, that probably makes you happy.

Now there’s a tool to help you see if you’ll stay smiling or just decide to get out of the way.

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