Following up this article ..0.27 microSv/h from snow in Saint Louis
0.36 microSv/h (42.9 CPM) was measured from snowfall in Saint Louis on 1/13/2012.
Also, back in 6/28/2011, they measured 0.47 microSv/h from the ground in Kansas city.
http://www.youtube.com/watch?v=39FuYJL5nR8
Iori Mochizuki