I have some ideas for a mod.
There would be different Intensities in Clouds, Rain, Snow and Wind.
Clear (The Sky is clear of clouds entirely. Very rare.)
Mostly Clear (The Sky is mostly clear of clouds, only a few appear. Somewhat rare.)
Partly Cloudy (The sky looks like it does now. The most common one.)
Cloudy (Significantly more clouds than usual. Rare.)
Overcast (Extremely rare. The entire sky is covered by clouds. Dark.)
Hurricane (This is a special type. I'll get to it later.)
Drizzle (A small drizzle. Usually not very long. Somewhat rare.)
Light Rain (A bit of rain. Not very intense. Common.)
Medium Rain (The amount of rain we have now. Most common.)
Heavy Downpour (Quite a lot of rain. Rare.)
Torrential Downpour (Special. I'll get to it.)
Hurricane. (I'll also get to this one.)
No Wind (No wind whatsoever. Somewhat rare.)
Breezy (A little wind. Common.)
Windy (Normal amount of wind. Most common.)
Extremely Windy (Very Windy. Rare.)
Storm Wind (Extremely rare, lots of wind.
We also have snow Intensities! Same as the rain in rarity.
Now we get on to the Events.
DEW: This is a special event. When the dew event happens, everything will appear brighter and reflect more light. Usually comes with fog.
THUNDERSTORMS: Rare. There's a lot of clouds. Cloudy to Cloud Cover. Here, there's a lot of wind. Perhaps windy to extremely windy, and usually heavy downpour in rain.
HAIL: Very rare. Hail is special. Usually minor wind, medium snow. The special thing about this is that every once in a while an ice block falls from the sky, hitting the ground and being placed with the ice block break sound. If something, including you, gets hit you will be damaged and the ice block will shatter.
FOGGY: Ever so often you'll wake up one morning and it will be foggy. The world will also have the dew event. It's not very rare, usually coming in the mornings or after rain. In the case of rain it's more often going to come after either light or heavy rain. Won't come after medium rain. Usually lasts half a day.
RAINSTORMS: Rainstorms are very rare. The sky will have Overcast clouds, and the rain will be a torrential downpour. This is the only time torrential downpour will occur. The foggy event is practically guaranteed after this.
SNOW: If the world is set to, say, heavy downpour, any snow biomes will experience heavy downpour except in snow. If a rainstorm happens, then in snow biomes a snowstorm will happen. It's very rare, but it can now also snow in any biome except desert and jungle. More common in colder biomes. We'll get to temperature soon.
SNOWSTORM: As rare as rainstorm. Functions the same. If a rainstorm happens, a snowstorm will happen in snow biomes. Snowstorms can happen by themselves without a rainstorm, but not the other way around. On insanely rare occasions a snowstorm can happen in any biome except desert and jungle. A rainstorm does not need to occur if a snowstorm does, but a snowstorm happens if a rainstorm does.
HURRICANE: On very rare occasions a hurricane will occur. Hurricane clouds means a very dark cloud cover. Hurricane winds and hurricane rain. Hurricanes are dangerous, and can even pick up loose blocks like sand, gravel, other light soils like red sand and fling them around. Stay inside during this.
BLIZZARD: Works the same way with the rainstorm and snowstorm. A blizzard will happen in snow biomes if a hurricane does elsewhere, but a blizzard can also happen on it's own without a hurricane in snow biomes. Can also, on insanely rare occasions happen in a normal biome. Also extremely dangerous. Stay inside.
RAINBOW: Usually appears along with the dew. So, a foggy event happens after a rainstorm and dew comes along with it. Boom, rainbow.
NOW, ON TO SOME MORE THINGS.
Crops grow faster by 5% each rain level. Drizzle allows them to grow 5%, light rain 10%, medium rain 15%, and so on. The only exception is hurricane. That rips crops right out of the ground if not shielded from the wind.
Trees can also 'fall over' during hurricanes. They can 'collapse' and smash through any structure they hit apart from obsidian, bedrock and portal blocks.
Fishing chances and speed increase by 5%, 10% etc. per rain level, including Hurricane this time. Although why you would go outside in a hurricane, I don't know.
With heavy downpour, torrential downpour and hurricane there's a chance of flooding. The deepest blocks in a fifty block area have a chance of being flooded with water. The chances, intensity and radius increases with more rain. That's why you should add big holes around your base to 'drain' water. It'll spawn there instead of somewhere important.
Climates. Blizzard, Freezing, Cold, Warm, Hot, Burning are the temperatures. Cold and freezing appear in cold and freezing climates, burning usually appears in deserts and hot appears in jungles and things like that. Blizzard is a special climate only appearing in blizzards. You move slower in colder temperatures and exhaust hunger in hotter ones faster.
Many things can change the temperature. Wind speed, for example. Wind chill has a part. If you're in water full of ice your temperature will drop rapidly. Water in hot biomes however will cool you off. Rain also changes the temperature.
If your temperature drops too low, you'll experience this. 0 Degrees Celsius, you'll walk slower. -10 Degrees Celsius, you'll walk very slow. -20 Degrees Celsius and your vision blurs. -30 and you begin to to freeze. A 'frost' effect takes hold which makes you mine slower and build slower. -40 Degrees is only possible in Blizzards. You'll get a 'frost-bite' debuff which makes you walk extremely slow, mine with mining fatigue 2 and other bad things. This is including wind-chill and other effects.
The effects of cold can be weakened by wearing leather.
Cold temperatures severly reduce growing speed of crops. No crop can grow properly in the desert without an abundance of water and shade.
Shade lowers your temperature, and you can get a heat-stroke debuff if your temperature rises too much. Say, 40 Degrees Celsius. This is bad and can kill you if you don't jump in water or enter the shade quickly.
Dry and wet climates also exist. Don't know what to do with those.
Puddles appear in rain and after rain. The music changes during hurricanes and blizzards.
Wind direction. Wind direction can affect the speed and trajectory of arrows and snowballs, but only fast wind. A little breeze does nothing.
Heavy wind can push you around. You can get damaged by hurricanes at random.
Tiled dirt gets hydrated in rain.
Blizzards give you the 'frost-bite' debuff if the temperature drops too much. Blizzards also give you the 'snow-blindness' debuff if you're out too long. Blindness except the black is white and it gets more intense the longer you're out there.
You can raise your temperature by standing near fire, torches or lava. A cloud-less day will also have high temperatures, while a foggy and cloud-cover may not.
Overall, hurricanes and blizzards are very dangerous. Avoid at all costs. Remove any nearby trees incase they fall on your house, bring any animals you want to live inside and shield your crops from the wind. Build small pits near your house to 'drain' the water. With blizzards you need some sort of heat. A fire, perhaps. Lots of torches. You don't want to die. You also need a lot of food in cold climates.
Also, on occasion at night you can see meteor showers and comets whiz by. In winter areas you can see the Aurora Borealis on occasion. The Aurora Borealis messes with redstone by turning it all on unless you put a certain 'energy remover' block near it. All redstone within a 20 block radius of it will work normal.
Also, how about a weather predictor? It can predict what will happen in the next, say, four days. The first day has a 90% accuracy rate. The second has a 70%, third has a 50%, and the last has a 30%. It may say 'heavy rain tomorrow with heavy clouds, light rain the third day with little clouds, no rain the next with cloud cover, and hail the fourth day with lots of clouds. An Aurora will happen the second day, comet trail visible at night on the fourth.'
The only exception is hurricanes and blizzards, which always have a 100% accuracy rate. It will blink red and make a warning noise when a hurricane is predicted. Enough time to set things up, move your animals inside, gather enough food to wait it out, cut down nearby trees, place drain holes, cover your crops and otherwise make it so you won't die.
Hurricanes and blizzards can last from 2 to 3 days. It's possible to venture out in a hurricane if you're brave enough. I would not go out in a blizzard, even to see the Aurora. Oh, wait, an aurora? Better place some 'energy' blocks around my redstone...
There can be new enemies and mobs in rain and snowstorms. Creepers may become supercharged during aurora's. Meteor showers can make enemies neutral... whatever.