Here’s the fact:
On Monday morning, the National Weather Service predicted storm-total snowfall amounts of 20 – 30″ for New York City. As of 9 am EST Tuesday, snowfall amounts in the city ranged from 7.8″ in Central Park to 11″ at La Guardia Airport, with just 1 – 2″ more snow likely.
In the NYC area, we were braced for a hurricane-scale disaster. Officials are feeling sheepish. But:
So what went wrong with the forecast? Heavy snow forecasts are notoriously difficult, since our computer models struggle to accurately predict where the very narrow bands of heavy snow with snowfall rates of 2 – 4″ per hour will set up. Furthermore, an error of 50 miles in predicting the track of the storm can make a huge difference in snowfall amounts, and a 50-mile error in track in a 24-hour forecast is fairly common for a storm system 1000 miles across. The 7 am EST (12 UTC) Monday run of what is usually our top forecast model, the European model, predicted that the storm would track about 100 miles farther west than it actually did. The American GFS model, which just underwent a significant upgrade over the past month to give it increased horizontal resolution, performed better, putting the storm farther to the east. Forecasts that relied too heavily on the European model put too much snow over New York City. The heaviest snows were about 50 miles east of the city, over central Long Island (Islip Airport, located 50 miles east of New York City, got 20.9″ of snow as of 9 am EST Tuesday.) Moral of the story: the European model, which famously out-predicted the GFS model during Hurricane Sandy, is not always right.
There is more risk and nuance in weather forecasts than the public is interested in consuming so it is a challenge to craft a message that gets attention, is not “hype”, yet has actionable information.
Believe me, communicating risk and uncertainty to those not trained is nearly impossible.