No.4 isn't Káťa, I'm afraid, George, or any other opera beginning with the letter K.

No correct that, Number 2 is La Cenerentola. I recognise 5,but blow me, (to use quaint old fashioned usage) if I can say what it is.

OK, I'm not totally sober.

Clue: No.1 is French, No.4 Russian.

Well, for non-French and Russian storms, the daddy of them all is the opening of Otello.

And from the German side, the opening of Walkure.

George has mentioned a particularly apposite Czech example.

There is a little storm in Il barbiere (I'm not sure Rossini didn't recycle the Cenerentola storm there, or the other way around.) 

Idomeneo from a more sedate tradition.

And in Handel operas folk are always going on about how their emotions are raging like a storm.  This is mainly to cue spectacular displays of coloratura.  I suggest we omit metaphorical storms like that as it would open up the field too far.

But storms in opera are often metaphorical in that they represent the inner turmoil of the characters - such as those in Act 1 of Peter Grimes, Act 3 of Rigoletto, Act 3 of Kat'a Kabanova and at the start of Act 3 of Siegfried (the weather throughout Billy Budd is a metaphor, but no storms there - just mist and treacherous ominous calm)

Other operatic storms portray the power of the supernatural: Die Frau Ohne Schatten - where the Dyer's Wife (I think - I'm at work without access to score or Kobbe and whipping out the iPod for a quick listen would be a bit tactless) explicitly says during the storm in Act 2 that dark forces are in play; and in Der fliegende Hollander, Freischutz, Les Pecheurs des Perles and Oberon.  And the row between Titania and Oberon causes all sorts of climate chaos in A Midsummer Night's Dream, but that's in the play and we don't encounter the storm itself in the opera so it probably doesn't count.

Sometimes of course the divine intervention is direct - we've already mentioned the hapless Boetians in Il Ritorno d'Ulisse on this thread.

Then there's the opening storm in Ades, The Tempest, very much modelled on the Otello one I felt, and I found it a little disappointing - not nearly magically scary enough!