The rain value from the wxt has been a constant zero:
http://www.eol.ucar.edu/isf/projects/SOAS/isfs/qcdata/plots/20130606/precip_20130606.png
The current output message looks like so:
0R0,Dm=103D,Sm=0.8M,Ta=20.5C,Ua=94.2P,Pa=1.0072B,Rc=0.00M,Hc=0.0M,Vs=12.8V\r\n
...