Very common. See #6: https://idioms.thefreedictionary.com/call+for

Hi, I don't think any English native speaker would say "they are calling for thunderstorms" this is not an English expression! where did you hear this? Could you have misheard?

It's about the forecast. "They are calling for" is a common expression for talking about the upcoming weather. "They" refers to the weather forecasters. Example: I need to get some supplies because they're calling for a lot of snow next Monday.

If I were to restate the sentence as "They are forecasting for thunderstorms", the potential ambiguity would be removed, ie calling for is to say, to forecast

Something big is going to happen