The University of Maryland Dept. of Atmospheric and Oceanic Science prepared an Excellent (yet small) map of the expected path of the plume from Fukushima, Japan. If you are interested in the path click HERE . As for the expected date March 24 through March 26 would be my best chance of detecting it, although from the map it may be passing to the north and hitting Kansas.
Today I did the 15 minute swipe test a little later than usual. The weather was 70's, winds from the south, and it was overcast and looked as though it was about to rain. Here is the raw data:
Driveway = 9.6 CPM (counts per minute)
Swipe (from front window) = 10.8 CPM
Interior House = 11.2 CPM
Not sure why the radiation levels have been dropping. Could be solar X-rays are sheilded by the clouds, the wind has blown a lot of the dust out of the air (soil contains naturally occurring radioactive materials) or I may have missed the plume!
PM1703m Scintillator = 7 microR / hr; PM1208 Geiger Counter Watch = 13 microS / hr.