AIR MAIL
Where today’s air came from
The air arriving over Pine City about 5,000 feet above the ground was over the southern Plains three days ago, and over the central Plains a day ago, about 950 miles back along its path. It came down from about 9,000 feet up, warming and drying as it sank. Near the ground the air came from a point about 470 miles to the south; at 10,000 feet, from the northern Plains. Traced back 72 hours through NOAA’s hourly RAP analyses, nine paths at each of three heights.