UPDATED 3/26: The above map is the one Professor Van Hippel was referring to that Rachel said we'd put on the blog. Below, a wider view of the effect of wind patterns on radiation dispersal.
"On March 15, the radioactive cloud from Fukushima reactor was transported inland, hitting the CTBTO station in Takasaki." --From the report, "Accident in the Japanese NPP Fukushima: Large emissions of Cesium-137 and Iodine- 131/Spread of Radioactivity/ weather currently favourable/low level radioactivity observed in Iceland (Update: 24 March 2011 16:00)" (pdf)
ADDING: Here's an animated version of this map: