AIR MAIL
Where today’s air came from
The air arriving over Two Rivers about 5,000 feet above the ground was over the northern Plains three days ago, and over the Great Lakes a day ago, about 1,170 miles back along its path. The nine paths traced from around the city fan out, so treat that as a best guess. Near the ground the air came from the Great Lakes; 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.