AIR MAIL
Where today’s air came from
The air arriving over Lake Fremont about 5,000 feet above the ground was over the Great Basin three days ago, and over the southern Plains a day ago, about 1,420 miles back along its path. Most of the nine paths traced from around the city agree. It came down from about 12,100 feet up, warming and drying as it sank. Near the ground the air came from the Mississippi Valley; at 10,000 feet, from Texas. Traced back 72 hours through NOAA’s hourly RAP analyses, nine paths at each of three heights.