AIR MAIL
Where today’s air came from
The air arriving over Canton about 5,000 feet above the ground was over the Maritimes three days ago, and over New England a day ago, about 780 miles back along its path. It came down from about 10,800 feet up, warming and drying as it sank. Near the ground the air came from Canada; at 10,000 feet, from the Atlantic off the Carolinas. Traced back 72 hours through NOAA’s hourly RAP analyses and the GFS beyond them, nine paths at each of three heights.