Storm has displayed minute control over rain before, to the extent that she doesn't stop the rain everywhere, just directly above a chosen area(herself, a friend, a group of friends). Even during funerals(see Scott's). Or she could just let the rain fall on her anyways, as she is immune to temperature variations, and could just dry her clothes later easily with induced evaporation. It's an affront to the character to be using an umbrella either way.
Anyways, I'm more pissed about Fox making Storm a bad guy yet again. She's shown to defect to Magneto's side along with Beast and Nightcrawler, obviously because 'her great hero' Mystique was killed by Jean.
In the original DPS, when Ororo learned that Jean had killed the D'Bari star system and billions of its inhabitants, she was in a moral quandary, but she chose to fight to defend Jean from the Shi'Ar nonetheless.
Attachment 71526
Of course, the films have never gone out of their way to show Ororo and Jean as friends the way Claremont did, so the point it moot in this 'verse, but it is annoying to see Fox do this[again, make Storm on the bad guys side, as they did in Apocalypse].
I can't wait to see goddess Ororo in the MCU, bringing the rains down in Africa!