How can you exclude OZ? It has a flying cow!
That leaves "Twister" which was a great way to apply formula scriptwriting with awesome fx (and a flying cow!). As long as we are talking weather-fiction, there is "The Day After Tomorrow" which was an entertaining suspension of disbeleif. But for true science-fiction, you can hardly beat "An Inconvenient Truth." It won an Oscar!
If you will allow cartoon episodes, I would nominate "The Simpsons - Mr. Plow"