grammar - Use of particle や with も

I was reading a textbook and found this sentence:

海や山もあれるそうです。

I don't understand what the や is doing there with も.

The full piece where it comes from is:

あさっての夕方ごろからくずれるそうです。気温も下がるそうです。海や山もあれるそうです。

And the person was answering to a question about weather forecasts.

Is that supposed to mean something like "Both the sea and the mountain..." or is it just a typo?

Answer

あさっての夕方ごろからくずれるそうです。気温も下がるそうです。海や山もあれるそうです。

It's using 山も to say "Adding to / Beside くずれる(=雨が降る/it will rain) and 気温が下がる(temperature will drop), 海や山 will also be rough."

The も in 気温も is being used in the same way: "Adding to / Beside くずれる(the rain), the temperature will drop, too."

The や implies that places/areas other than 海と山 will also be rough. Compare:

海と山が荒れる -- (Just) The sea and mountains will be rough.
海と山も荒れる -- Also, the sea and mountains will be rough.
海も山も荒れる -- (Also,) Both the sea and mountains will be rough.
海や山が荒れる -- The sea and mountains and other places will be rough.
海や山も荒れる -- Also, the sea and mountains and other places will be rough.