[onewhitetree]

I tend to think of the weather in ME as more of a literary device, and less as the result of scientific probability. The Silmarillion describes a general change in the climate and weather patterns toward the end of the Numenorean glory days. As the culture of the island became deceived by Sauron into worship of Morgoth, Tolkien wrote that the weather became less orderly, so to speak. Up until that point, it rained when crops were thirsty, there was a breeze when the summer sun became hot, and winters certainly came once a year, but were not over-harsh. Once the hearts of Men had turned away from their noble heritage, powerful storms arose, climates changed for the worse, and great earthquakes changed the landscape. Al Gore would have been devastated.

Think of all the instances where weather is described: the idyllic sunshine of the Shire, the sorcerous storm at Caradhras, the noxious black clouds of Mordor, etc. These are all effective plot devices that allow the reader to discern nuances in the story. Even at the very start of the Second Age, the cornerstones of the climate/natural world, the Sun and Moon, are established as powerful symbols of the struggle between Good and Evil.

The symbolism here isn't limited to one-off occurrences like storms when Saruman is angry and volcanic explosions when Sauron's in the kitchen. It is embedded in the fabric of ME. The Shire, Rohan, Lothlorien - these are wholesome places, and Tolkien describes this not in matter-of-fact statements but in the weaving of many subtle elements that create the idea of wholesomeness in the reader's mind.