Yesterday morning it rained pretty hard. 4 sites with tipping buckets (se4, nw2, se5 and sw2) showed tips between 09:00 and 10:30 CDT. (The data from nw2 was brought by sneaker-net.)
Logged into nw3 and dumped the rain data. Did not show any tips at nw3 during that time.
According to Sensor List those 5 sites (2 x PAM, 2 x 40', 1 x 100') are the only ones with tipping buckets.