If a storm is four or more days away, the forecast will offer chances of wintry precipitation in general — snow and sleet — at basically any amount (over 0.25 inches liquid water-equivalent).
The National Weather Service can offer this new product in large part due to the increase in skill that the U.S. models have achieved over the past couple of years. The forecast combines the output from a large number of models to generate a good estimate as to where winter weather impacts will likely be felt in the week to come — information that is invaluable to decision-makers and emergency managers.
This is a nice addition to the winter weather tools offered by the Weather Prediction Center, which also include freezing rain forecasts, impact graphics and discussions by meteorologists.
Last week, the local office of the National Weather Service in Sterling, Va., announced that it will provide long-range winter storm “threat levels” out to seven days, as well. The graphics are similar to the Storm Prediction Center’s severe weather outlooks in the way it categorizes the threat of winter weather impacts from “slight” to “high.”