Moriarty Weather Information
The best and latest non-web source of how to interpret weather for soaring conditions is Tom Bradbury's Meteorology and Flight (3rd edition). One excellent part of Tom's book is near the end where he summarizes a list of weather features most favorable to thermal flying. To round his approach out, Dennis Pagen's Understanding The Sky really adds a lot as it focuses on how to read terrain and conditions, and is thus more aimed at certain strategic/tactical actual flying.
At the bottom of this page also find links to weather archive sites. Use these sites if you want to study weather on a given day in the past for which you understand the soaring conditions that occurred on that day.
The information websites at the bottom of the page contain a pletora of valuable information, lessons, and tutorials.
(in approximate order of usefulness)
Weather data archives
Informational and Educational