Just a few common idioms associated with weather.
o Rain check
o Rain delay
o On account of good weather
o Raining cats and dogs
o Come rain or sunshine
o When it rains it pours.
There is no telling the number of weather related idioms. Those were just a few which came to mind.
Weather is a common receiver of attention. Almost every news broadcast relays a weather forecast. Generally, when people are planning their week in advance, they check the weather.
At some point in time, weather became integrated with our every day language. Everyday circumstances are often described by weather orientated idioms like "come rain or sunshine" or "how about a rain check."
Without previous exposure to these idioms, their meaning falls short of comprehension. At some point during out language acquisition, we learn to identify their meaning. That is the essence of an idiom.
Generally, one or two idiom exist for a place or circumstance. An example of this is "when in Rome" or "Rome was not build in one day."
Perhaps the effective magnitude of weather on our everyday lives gives rise to a high number of idioms.