Take a normal travel route in your game and add weather. That ogre encounter you planned can take on a different level of difficult by adding rain, fog, snow or a fricking tornado! I've never had a tornado in my game. I may need to do that. When I do add an environmental element to an encounter I usually add some modifiers to make it relevant.
Say the group is headed north on a road they've travel hundreds of times, but the day is rainy and patchy fog hangs in the air. When Mr. Ogre Grumpy Pants bursts through the fog and rumbles towards the party, wielding a barn door as a club what happens now?
- Everyone with a one handed weapon is at -1 to hit and to damage.
- Two handed weapons are -2 to hit and to damage. When you can't find good footing then it's more difficult to drive a strike home.
- A miss requires a Dex roll. A failure could means they get twisted up and fall. Could mean the pommel of the weapon is wet and slips out their hand. Requiring a round to get up or get retrieve a weapon.
I wrote the rain away. The rain stopped here. I must be magic.