This is a more general version of the #uksnow map idea. It's a crowd-sourced weather map which relies on the fact that any one individual tweet about the weather might be inaccurate but given a large enough sample, enough people will mention the weather in their area to make this a workable idea. It doesn't require people to tweet in a particular format.
To get info
Have an array of weather words in various languages (rain, hail, snow, schnee, ame, yuki) every 5 minutes: foreach weatherword search twitter for that word http://search.twitter.com/search.atom?q=rain retrieve latest 100 tweets foreach get user info http://twitter.com/users/show.xml?screen_name=username get user.location if available geocode save: username, time, lat, long, geotude, weatherword Remove any tweets about this weatherword older than 6 hours.
To display info
Show a Google map Based on current Zoom level, split the current map into about 100 geotudes foreach geotude search database for any weather results for that block (probably using an ilike "1234%" on the geotude field) sort by weatherword count descending draw an icon on top of that block to show the most common weatherword If the user zooms in, recalculate geotudes and repeat.
I quite like that this uses geotudes which I think are an excellent idea.