What does "Active Weather Patterns" mean? I just read that Cassini discovered titan had "active Weather patterns". 

What does that mean?
It means that Titan has weather (driven by methane rather than water) and that it's weather changes with the seasons. Cassini has been observing Titan for almost half of a Titan year, which is 29.457 times longer than is our year. Titan's weather patterns (where it's cloudy, where it rains) has visibly changed over this time, just as weather patterns here change from summer to winter / winter to summer.