[idvusers] executing fog products in IDV

I am an undergraduate and very new to IDV.

Is it possible to create composite images out of McIDAS AREA files and surface 
plots (GEMPAK or netCDF files)?

specifically, I am trying to evaluate a fog product and one of the criteria is 
that surface temperature - longwave (ch4 on GOES) brightness temperature < 4K.

I have AREA files of satellite data and GEMPAK/netCDF files of surface 
temperature, but I don't know what to tell IDV in a formula to get a composite 
of the two.

Thank you,
Caitlin Hart
SUNY Brockport Meteorology