Snow warning bump

This is going to take some getting used to. For decades a forecast of 4 inches or more in Philadelphia was enough for the National Weather Service to hoist a "winter storm warning."

This winter, however, 4 inches won't cut it. It will take a forecast of at least 5 inches to raise the flag in and around Philadelphia and in South Jersey.

At a briefing Tuesday, meteorologists from the Mount Holly office rolled out a new winter protocol to take effect Dec. 1.

In addition to raising the "warning" threshold, the advisory criteria will become 2 to 5 inches; formerly, it was 2 to 4.

In addition, starting within three of a snow event, the weather service will post "goal post" maps that will show three possible ranges for potential accumulations  – minimum, "most likely," and maximum .

A companion chart will list accumulation probabilities for selected towns.

Meteorologist Greg Heavener allowed that those terms "might not be the best," but in the weather world, certain accommodations must be made with the language. (See "normal.")

Given the chaotic nature of the atmosphere, holes in the worldwide observation network, and computer imperfections, Heavener said that posting probabilities and possible ranges would better serve the public, given the capriciousness, and occasional downright insanity, of snowfall totals.

Speaking of computers, the weather service said it would be consulting 57 different models, heavily weighted toward the European's, which tend to be a tad snowier.

As for the why of the change from a 4-inch to a 5-inch threshold, one reason was to bring Mount Holly in line with other weather-service offices in the Midatlantic and the Northeast.

Not that there's anything magical about the number "5," which is something it has in common with "4."

Traditionally, said Joe Miketta, the office's warning specialist, the trigger for a warning was related to "what is inconvenient and what is a threat."

Obviously, that's a subjective call. But in considering the 4-inch threshold, the thinking was, "we need more snow than that to cause problems."

Don't worry, they are aware in Mount Holly that sometimes it takes a lot less to cause problems.