by Philip Lutzak - June 2007


Figure 1. Visible satellite image of the Great Lakes from 2006-07-28 at 12Z. Note the fog bank (white and gray tones)  that has formed overnight on Lake Huron southwest of the entrance to Georgian Bay. Courtesy Penn State Meteorology. Figure 2. Relief map of the entrance to Georgian Bay, annotated to show the average height of the hills on either side of the entrance. Courtesy Tele Atlas. Large version.


  In Figure 1, above left, is a visible satellite image of the Great Lakes region on the morning of July 28, 2006. The area of white and grays southwest of Georgian Bay is a fog bank that had formed on Lake Huron overnight. Figure 2 shows a close-up image of the area where the fog bank formed in front of the bay entrance. Manitoulin Island is on the northwest side, with the Bruce Peninsula on the southeastern side of the inlet. The little feature marked 660 feet is Lonely Island.


  Figure 3 below shows a close-up of the surface map in the area on the morning of July 28th. Note the air temperatures in the area were all around 68-70 F, with very light to calm winds. Figure 4 shows the water temperatures in northern Lake Huron were running in the low seventies. So we can see how during the night the air overlying the Lake became cooler than the water that it lay over, allowing the large area of fog to form.


Figure 3. Close-up of surface analysis from 2006-07-28 at 12Z. Courtesy HPC. Figure 4. 2006-08-01 water temperatures on the Great Lakes. Courtesy Coastwatch.


  As the cold front visible in Figure 3 approached later in the morning, the winds turned southwest and increased in speed (see the 2006-07-28 18Z surface map). As the southwest winds hit the stagnant fog bank, they pushed it forward towards the bay entrance, but since the fog was only a few hundred feet in height, it backed up against the 600 feet or so land masses but continued on through the entrance and then plumed out into Georgian Bay. Here’s a short movie of the fog bank on 2006-07-28. Of particular interest in the last frame of the movie, also visible in the satellite image in Figure 5 below, is the dark spot in the middle of the fog plume – that’s Lonely Island, which the fog was forced to go around.


Figure 5. Visible satellite image from 2006-07-28 2115, showing the fog bank getting forced through the Georgian Bay entrance. Courtesy NOAA.