No need for a Weather Generator, if you take a particular look at Climate.
Think of Climate as an Endless War between Good and Evil, only in this case, Hot and Cold.
This war, instead of progressing slowly, progresses rapidly and annoyingly, with one Battle Front coming through after another, every few days. (The term 'Front', ala Warm Front or Cold Front, was taken from a Real World War and it's fronts.)
So, it turns cold. Then hot. Then cold. Then hot. Then colder. Then hotter. Then less cold. Then less hot. In mad succession, never ending.
Each front brings storms of wind and rain, followed by gusty winds, followed by partly cloudy weather or sunny weather. Occasionally, a slow moving or nearly stationary front brings a long period of storms and rain.
If it is summer, these storms are rain storms.
If it is winter, these storms are snow storms (or, occasionally, ice storms or sleet storms.)
If it is spring or autumn, the storms could be of any kind.
If the storms are gentle, light rain or snow falls.
If the storms are heavy, thunderstorms or thundersnow occurs.
If the storms are strong, severe thunderstorms and tornadoes, or very deep snow and blizzard conditions, occur.
Now ...
There is always some Clown out there, in the D&D multiverse, who thinks he should be the guy running the weather, and not the weather.
Or the druids decide they are going to get revenge for the latest attack on their forest.
Or the elementals were let into the world, and they want to show off.
Or the efreeti decide to heat things up a bit.
Or the lich decides winter would be more appropriate (even they it is still July.)
Counterforces move to try to correct the weather imbalance, which of course stokes more magical interference in the weather ... the chain reaction of this can lead to some pretty serious problems worldwide.
I mean, even in the Real World, the weather is unpredictable and downright freakish at times. Throw in magic and rabble rousers, and the occasional troublemaker, and a lot of faerie and elemental forces that want to have it their way, and counterforces, and just about anything you want could happen.
Hurricanes?
Hurricanes normally occur over warm water of 80 degrees or higher (27 celsius or higher.) Normally, they begin over areas where the weather is (paradoxically) tranquil and calm, down in the tropics.
Once started, they - much like bulls - rush along, mowing everything down in their path.
Since hurricanes are such enormous weather systems, affecting in some cases more than one million square miles of surface area in one way or another, they can throw side effects into regions thousands of miles from themselves.
Fooling around with hurricanes using magic is ... well ... dangerous. It is much like trying to control a raging forest fire with a garden hose. Unless you've got some pretty powerful magic, you may unleash something you never intended, playing around with such forces.
There are some campaigns where the weather is artificially generated by resident faerie beings or wizards, and one of them is the Flanaess region of Oerth (Greyhawk.)
There, the climate is warm temperate or subtropical from Veluna and northern Furyondy, east through the Shieldlands, to northern Nyrond and the Theocracy of the Pale, across the mountains to Ratik, and offshore to a point well north of the Lendore Isles.
West of the Crystalmists, the climate is subtropical all the way to the ocean north of Zeif, and warm temperate up through Tusmit.
*North* of this line, the climate turns from warm temperate to subarctic within a hundred miles, except only in Perrenland which is cold temperate.
What does subarctic mean? What does it mean versus temperate?
Simple:
Tropical = always summer
Subtropical = always summer, but occasional cold snaps for 4 months
Very Warm temperate = 6 months of summer (2 to 3 months of winter.)
Warm temperate = 4 months of summer, 4 months of winter.
Cold temperate = 3 months of summer, 5 months of winter.
Frigid temperate = 3 months of summer, 6 months of winter.
Subarctic = 3 months of summer, 7 to 9 months of winter.
Tundra = 2 months of (quite variable) summer, 9 to 10 months of winter.
Arctic = Always winter.
Final thing: A classic rule of thumb about the Temperate climate is that you are always importing somebody else's climate. You never really have your own (and you wish the climate from somewhere else would leave, and it does, but then you wish what replaced it would go away too, and ...)
