AIR MAIL
Where today’s air came from
The air arriving over Northfield about 5,000 feet above the ground was over New England three days ago, about 1,840 miles back along its path. The nine paths traced from around the city fan out, so treat that as a best guess. It rose from near the ground on the way. Near the ground the air came from the North Atlantic; at 10,000 feet, from a point about 470 miles to the south. Traced back 72 hours through NOAA’s hourly RAP analyses and the GFS beyond them, nine paths at each of three heights.