You Don't Need A Weatherman To Know Which Way The Wind Blows

One indication of a strong thermal is when the roof of the AFSS flies past you at cloudbase:

TORNADO PUTS AFSS OUT OF SERVICE
A tornado ripped the roof off the Terre Haute, Indiana, automated flight service station (AFSS) on February 17, taking out many of the antennas and damaging radio and other equipment. Fortunately, no one was hurt. Telephone calls have been rerouted to other flight service stations, but Terre Haute radio frequencies are out of service. Adjacent AFSSs are providing in-flight services to pilots in or flying over Indiana using their own radio frequencies. A temporary roof already has been placed over the Terre Haute facility, and work is progressing on a new permanent roof. Radio repairs and recertification are scheduled for completion by March 16. The Terre Haute AFSS is targeting March 17 for return to full operations.