TROWAL stands for "trough of warm air aloft". There's pretty good web based presentations on trowals as well as isentropic analysis at:
TROWAL Identification (Lindstrom, Bachmeier, Martin)
http://www.cira.colostate.edu/ramm/visit/trowal.html
Isentropic Analysis (Moore)
http://meted.ucar.edu/isen_ana/index.htm
Heavy Banded Snow (Moore)
http://meted.ucar.edu/norlat/bandedsnow/
Winter Meteorological Processes in the Atmosphere (NWS Louisville)
http://www.crh.noaa.gov/lmk/soo/docu/forcing1.htm
As for analysis maps, here's a site:
College of DuPage
http://weather.cod.edu/analysis/analysis.isentropic.html
Regards,
Mike