It was March 2017, and a winter storm named Stella promised to deliver as much as a foot and a half of snow to New York City and parts of New Jersey. Officials pushed out blizzard warnings, suggesting the city was under imminent snowy siege.
But only seven inches fell. Gov. Chris Christie blasted forecasters. “I don’t know how much we should be paying these weather guys,” he said. “I’ve had my fill of the National Weather Service after seven and a half years.”
For anyone following the weather, forecasts for big storms are sometimes still roller-coaster rides — with sudden shifts in track or intensity. As a meteorologist who forecasts for a large urban market, I can attest to the frustration. Why can’t we get it right every time, given this era of 24/7 weather data, dozens of satellites and sophisticated computer models? The answer lies in the quirks between the most popular forecasting models.
Battle of the models
Computer forecast models have become the mainstay of weather prediction across North America and many other parts of the world. Run on fast supercomputers, these sophisticated mathematical models of the atmosphere have gotten better over the past couple of decades.
Human forecast skill has improved by approximately one day per decade. In other words, today’s four-day forecast is as accurate as a three-day forecast was a decade ago.
Forecasters in the United States routinely examine several models, but the two most discussed are the American and the European. When the models disagree on the track of a big storm, forecasters must often choose which they believe is most correct. This decision can make or break a critical forecast.
Most meteorologists agree that the European model is the most skillful. This was cemented in March 1993, when it correctly forecast the track and intensity of a historical nor’easter. Called the “Storm of the Century,” the storm dropped a blanket of heavy snow from the Gulf Coast to the northern tip of Maine.
The storm was a milestone for what is termed medium-range forecasting, or forecasts made three to seven days out. The European model nailed the prediction five days in advance. That meant officials could declare states of emergency before the first flakes ever flew.