where it got truly cold (well below freezing for extended periods of time) during that time of year (I've been to Canada, but during the summer). I do, however, live in an area of the country where weather plays a very major role in day-to-day activities. In the middle of the United States, we experience just about every kind of weather except for extended bitter cold and hurricanes. Massive thunderstorms - check, flooding rains (sometimes flash flooding) - check, heavy snow - check, drought - check, extreme heat (and humidity) - check, below freezing temperatures for several days at a time - check, tornadoes - check (in an exponential fashion), earthquakes (though not massive damaging ones) - check, sudden significant temperature changes (up or down) - check, strong winds (greater than 30 mph) - check, major ice storms (power was out for large areas for weeks) - check.
Now, how come all these things that affect my everyday activity don't make it into affecting my activities in a campaign? For one, I haven't seen to many good random weather generators that actually reflect real weather patterns (granted, even people with degrees, years of experience and massive computer simulations can't even really predict weather outside of a 72-hour window). For two, weather really isn't very interesting from a story development perspective. For three, the players (short of super powerful games) can't really do anything about the weather. For four, it's a pain in the butt to try to keep up with when there are hp totals and saving throws to worry about.
because weather is an encounter builder. If you are going to use an elemental in a game, why not do it during a thunderstorm (air or water) or a dust storm (air or earth)? Make the scene interesting, memorable - nobody remembers that time they saw a couple of elementals just hanging out, but they might (should) remember the time they were caught in a flash flood and saved by the water elemental who was surfing the canyon.
All that's great (no, not really), but that's not really using weather effectively. Ok, so let's use it to affect the game. Want to slow down a party's trek to a given location - snow/ice/floods. Want to create tension in a region - extended drought or persistent heavy fog. Want to get rid of a base of operations to force the players to be more self-sufficient - hurricane along acoast or an EF5 tornado. The point is to make things interesting and different so that your players aren't tromping through the same thing over and over again.