Here's the basic definitions:
WEATHER: local meterological conditions
"My goodness, the weather has been horrendous lately, not a day without hail in the past month!"
WHETHER: doubt or choice between two alternatives
"I can't decide whether to have the Jelly Snake Trifle Extravaganza or the Deadly Chocolate Mint Mousse with Sprinkles."
WETHER: a castrated ram
"Hey Joe! The wether in the upper paddock is looking rather sleepy. Better get him his morning coffee!"
Our pal Dylan has a great way of remembering which spelling is which:
With weather, it's about whether there's a sun in the sky or a hurricane a-blowin'. Weather has an a in it.
All the questioning "W words" seem to start with "Wh" — eg "Who? What? Where? When? Why?", so if you're talking about whether as in "the choice", use the "Wh" version.
A wether is a castrated ram — that's why it's shorter!
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