AIR MAIL
Where today’s air came from
The air arriving over Spring Grove about 5,000 feet above the ground was over a point about 190 miles to the south three days ago, about 600 miles back along its path. The nine paths traced from around the city fan out, so treat that as a best guess. It came down from about 9,600 feet up, warming and drying as it sank. Near the ground the air came from the Great Lakes; at 10,000 feet, from a point about 300 miles to the south. Traced back 72 hours through NOAA’s hourly RAP analyses, nine paths at each of three heights.