AIR MAIL
Where today’s air came from
The air arriving over Vermillion about 5,000 feet above the ground was over a point about 390 miles to the south three days ago, and over the southern Plains a day ago, about 770 miles back along its path. It came down from about 9,500 feet up, warming and drying as it sank. Near the ground the air came from a point about 320 miles to the southeast; at 10,000 feet, from the southern Plains. Traced back 72 hours through NOAA’s hourly RAP analyses, nine paths at each of three heights.