I hail donjon as one of the most complete gennies I've come across in my years of worldbuilding. I've linked to it before, but I'd like to refer to it again, particularly the random weather generator
Personally I use the weather almost as its own character. At the time I'm drafting this post there is a massive scramble underway in NYC for the monster storm. School is cancelled, public transport is shut down, the harbor is closed, they're afraid the subways will flood, it's even managed to dampen (pun intended) a rather heated presidential campaign. So for the city that never sleeps to come to a grinding halt is a BIG deal.
**Update: the 900 mile wide civilization-drowning blight on the Eastern US of A (aka Hurricane Sandy) is responsible for 11-14 foot swells making landfall in NYC, resulting in thigh deep water on the surface streets, the complete flooding of 7 subway tunnels under the East River, and countless millions of dollars in property damage. Oh yeah and the largest scale blackout of the greatest city on Earth since 2003.
Rain in Seattle, smog in LA, neon lights in Las Vegas, every city has its staple environment - use that to the fullest. Or like with New York, that is no stranger to hard winters, a torrential rain can really throw things for a loop. What if it didn't rain in Seattle? How would the Emerald City handle an unexpected drought? I live way up in the Rocky Mountains where yearly drought is a concern when the winter doesn't give us enough snow. Everyone talks about the impending, doomsday earthquake we call "the Big One" that's expected to level the city. But get people talking about strange weather and two things are sure to come up: the flood of 1983 and the tornado that ripped through downtown in 1999. Very rare and memorable things. Work something like that into whatever setting. Is the storm raging now and everyone is stuck inside, or is it darkening the horizon? Were people adequately warned and prepared, or is it panic mode to grab what is left on the shelves? Or do your characters arrive as some of the first travel allowed back into the city and everything is a disaster area?
Let's say your road weary travelers didn't heed the advice of a local druid's forecast and supplied themselves for only a 5 day trek, which took a turn for the worse and became a 12 day harrowing plod. Because a freak blizzard struck and halted forward progress they had to take shelter in a none-too-splendid inn. The innkeeper swindles them on the price of the tiny room, which has its share of bedbugs, rats, a draft around the window, and a leaky roof. The proprietor knows as well as the adventurers that it's their only option. Either pay top dollar for the shabby digs, or it's back out into the snow and blow. How do they deal with that speed bump? Do they blame their intrepid leader who passed on the sage advice in order to get on the road? Do they bicker amongst themselves about whose turn it is to stoke the fire and empty the chamberpot? Maybe they have to hold members back from throttling the innkeeper and ending up in the local dungeon, for which they have no bail money. And go!
See? This alone is a story (or game session). It really doesn't matter where they were coming from, or their destination.