I've generated the weather in Mor-Thir for the entire year; it varies by latitude, but as the party discovered, there are times it is just plain hot. So hot, in fact, that they had to travel at half speed, or risk heatstroke!
But apart from heat, what other weather exists?
- Frigid - water freezes, and movement is half speed; save vs. Blast each turn, or take 1d4 damage, unless appropriately clothed!
- Cold - water freezes; take 1d4 cold damage per day, unless appropriately clothed.
- Cool/Warm - good traveling weather; no restrictions or danger.
- Hot - movement is half speed; water is consumed at double rate.
- Clear - no precipitation; clear to partly-cloudy.
- Rain - uncovered belongings get wet, and torches have a 25% chance to go out.
- Sleet - cold; heavy sleet can restrict travel.
- Snow - cold, and it can pile up and make for slow travel: moving over unpacked snow is half movement rate.
- Fog - reduces vision to 30'
- Windstorm - ranged weapons are useless; Hear Noises is at -4; visibility 20' in sandy or dusty locations.
- Blizzard - as Snow, but with visibility 20', and torches go out.
- Deluge - visibility 20', torches go out, -4 to Hear Noises, everything is soaked!
- Hailstorm - every round, exposed creatures (not in a building or cave) are attacked as by a level 2 fighter, for 1d4-1 damage!
- Tornado - 20% chance per hour for a tornado!
- Storm - visibility 60'; 1% chance of a lightning strike hitting a player per turn
As summer turns into fall, the days will get shorter and cooler, but when, no one knows. Well, a Shaman would know; that's the reason I pre-generate the weather, just in case someone goes asking around...
Though the last few holidays have gone by without much notice, something a bit strange happened on Brightest Night; Lawful characters gained a slight bonus to all throws! No one in the party had experienced it before, but something about actively seeking out adventure allowed them to feel the effects of the longest day.
Brightest Night is not the only holiday with associated bonuses, however. Beast Night and Dragonning (the fall and spring equinoxes, respectively) each give the same bonus to Neutral characters, and Darkest Day (the winter solstice) gives that bonus to creatures of Chaos. It is wise to note the turn of time!