To add to Mary's words of wizdom, you can get the Lasham view of the forecast for gliding from their website:
LashamWeather.co.uk
And you can sign up to receive it by email whenever one is issued, which isn't every day by any means.
There isn't an archive of old forecasts there, but if I remember correctly yesterday's forecast was for a possible 'the day of the year' - and the flights posted subsequently suggest that indeed it was, with the longest being over 800k and many flights of 300k and more. Certainly a day to expect lots of gaggles, plus lots of gliders flying along under cloud streets.