FUEL has 4 primary weather effects to mess with your racing experience, from mild to severe:
Rain / Sleet
This is a pretty mild effect that just causes your vehicle to lose a bit of grip on the slicker road. Overall, you will hardly notice it except for the visual effects on the screen.
When you see leaves and crap flying across your screen, then you're in windy conditions. It is the most common weather effect in races, and will become the bane of your existence. You see this isn't normal wind; it's hurricane-style wind that bats vehicles around like paper dolls, making them have a mind of their own. When all wheels are on the ground and you're on a road running straight, the vehicle will hunt around on its own ever so slightly. But, when you hit a bump and a wheel comes off the ground your vehicle will blatantly veer all over the place without your consent. This makes fish-taily vehicles that much harder to control. It also makes hugging the shoulder of roads and running on bumpy dirt trails aggravating, as your vehicle will bounce and hunt along grooves or in random directions causing you to fight it every step of the way. Going through wooded areas is even more frustrating as your vehicle seems to take on a preternatural ability to home in on every tree and obstacle you're trying to avoid. So, if you were tearing it up in free-ride mode or another race with a certain vehicle then find that same vehicle hard to control in a particular race ... it's probably the horrible wind they coded into the game and decided to add to every other race to present a "challenge" (ie: a big, fat, "fuck you" to your face).
There are a few races that feature twisters, and while they themselves are not too bad the effects they bring can be race-ending. For starters... you've got Wind... the shitty wind that bats your car around like a cat toy. This makes staying on the course and avoiding obstacles that much harder. Next you've got falling power line towers. There's not too many, and while you can usually make it passed or under them without incident there are a few that are hard to gauge and may wreck you. Finally, you have all the junk that the tornado randomly spawns and tosses at you: logs, junked cars, trucks, boulders. This storm acts like it has a personal vendetta against you, as if you slapped its wife and kicked its dog. Most obstacles can be avoided, and you'll have some great moments when you fly past (or over!) junk flying your way. But, there will be times when everything just nails you and you are gritting you teeth in frustration.
There is one race that utilizes dust storms, and it is a royal pain in the ass. Like the tornado, there's the mandatory wind that makes it harder to control your vehicle. However, instead of tossing junk at you now you just have your vision blocked ... a lot. The screen goes dark, your visibility is reduced to almost nothing, and you're stuck following the tail lights and GPS arrows to have any clue of where to go. You can't take shortcuts, because you can't see where they are. So, that basically neuters the main advantage you have. You can't see debris on the road up ahead, so you'll either slam into it or swerve out of control to miss it at the last second. You try to ramp off something onto another road and slam into a tree. Your opponents, being computer controlled, run along like nothing is wrong. So, it's insult to injury. On the race that has dust storms you will go in and out of several, but there isn't enough time in between them to really make up any significant ground. So, you have to just rely on solid driving and run the course several times to figure out all the turns and dead-falls.