South Bend, Indiana experienced high radiation on the night of June 6-7. Radiation readings on the Radiation Network and Black Cat systems soared into the thousands of CPM, hundreds of times above normal. Potrblog has shown in a new post that this was indeed a genuine reading, and not an equipment malfunction.
It can be seen from meteorological analysis that these high readings are likely to have come from Fukushima emissions. First, a series of steam and smoke events were visible on the Daiichi webcams several days prior to this event. Second, Potrblog noted 5x background radiation in St. Louis air readings shortly before this. The first graphic (click to enlarge) shows the wind direction and speed at the 18,000 foot level on June 6. There is a ridge in the middle of the country, which forces the wind off the Pacific north into Canada, where it dives down into Minnesota. The wind in Illinois is from the northwest, and is at a fairly high rate of speed (shown by the colors). But, over Michigan, the wind is from the northeast. This sets up a convergence zone where the wind piles up radionuclides. The second graphic shows the situation on the next day, June 7. Now the wind is from the north. The fire department in Traverse City, Michigan notified the NRC of high radiation readings. South Bend (80 miles east of Chicago) is south of Traverse City.
The third graphic depicts omega at 18,000 feet on June 6. The yellows and oranges indicate downward motion, while purples and blue indicate upward motion. We can see that South Bend was in a region of downward motion that day. The downward motion was still in place on the next day, as shown on the fourth graphic.
So, it appears that convergence of two different air streams at 18,000 feet piled up radionuclides in the South Bend area. Downward vertical motion sent it to the surface when the surface wind became calm. When the wind kicked up again at 4 AM, the radiation cleared out.
UPDATE: I’m not sure what to make of this, but the Longmont radiation monitor in Colorado had an enormous spike on June 3, according to the graphic. It is up around 114 uSv/hr, which is brutal. This was 3 days before the Indiana event, but the plume would have had to go up into central Canada, and then dive down into the US again.