SKYWARN is the official "organization" from the National Weather Service, that trains interested persons, and amateur radio operators how to identify severe storm related activities, and to alert the public by means of amateur radio to public safety agencies.
The ham frequencies are repeaters or simplex frequencies that are COMMONLY used by skywarn spotters with-in the respective county/region. These frequencies are not assigned to any SKYWARN group, since amateur radio frequencies are open to all operators.
When SKYWARN groups are activated by the National Weather Service, a "net" is set up, with a "net control" operator, who acts almost like a fire or police dispatcher. He or she takes information from mobile spotters in their region, and reports findings to the weather service, or public safety agencies.
Hope this helps explain everything to you.
I am a SKYWARN spotter, and enjoy every aspect of it.
for information on attending a training session, go to the National Weather Service webpage:
www.nws.noaa.gov/
search for your region, and follow the "SKYWARN" links.
73 and God Bless
Pete Strank
KC8TCS