AIR MAIL
Where today’s air came from
The air arriving over Charlestown about 5,000 feet above the ground was over the Great Lakes three days ago, about 960 miles back along its path. Most of the nine paths traced from around the city agree. It came down from about 9,500 feet up, warming and drying as it sank. Near the ground the air came from the Great Lakes; at 10,000 feet, from the northern Plains. It feels dry all the same. Traced back 72 hours through NOAA’s hourly RAP analyses, nine paths at each of three heights.