Weather conditions were just right on the morning of January 15 for snow flurries to fall from clouds which developed from the steam emmitted by factories and paper mills in Green Bay. As the steam from the smoke stacks rapidly rose into the frigid air, the moisture condensed, producing clouds. What made this morning unusual was the presence of a strong inversion, or warm layer aloft, which helps trap the moisture. The moisture then had a chance to coalesce and produce snowflakes. Up to an inch of snow fell in the Green Bay suburb of Allouez, downwind of the mills.
The Green Bay National Weather Service Doppler radar is so sensitive that it actually detected the light snow across the area, even though skies were clear elsewhere in northeast Wisconsin.
(Click on the images below for the full picture)
The picture at left is taken from the west side of Green Bay, looking toward the paper mills. The picture at right is a 1.5 degree elevation reflectivity image. Note how the precipitation is moving away from the mills, as light southwest winds blow the moisture over the bay.