Choose real shelter, not hopeful shelter
Start with a covered space that can genuinely hold your guest count. An indoor room, properly installed marquee or covered terrace counts. A large tree and a collection of umbrellas do not.
Ask whether the backup space can hold the ceremony layout, accessible seating and the people who need to work there. Check flooring, sides, lighting and safe power as well as the roof.
Set the decision time in advance
Agree on who makes the weather call and when. The venue, planner, celebrant, caterer and musicians may each need different lead times, so write one final deadline into the schedule.
A decision made early enough to move chairs calmly is usually better than a heroic last-minute gamble. You can still hope for a clearing while preparing the covered version.
Plan for wind, heat and cold too
Rain gets the attention, but wind can lift signs and table settings, heat can exhaust guests, and a sharp temperature drop can empty a dance floor. Ask your venue what happens in each case.
Secure lightweight decorations, avoid open flames in gusts, provide water and shade in heat, and arrange blankets or heaters only where the venue says they are safe.
Protect the guest journey
Think from the car park to the last dance. Are paths firm under rain? Is there somewhere to leave wet coats? Can older guests reach the covered space without crossing mud? Who tells everyone if the ceremony moves?
A short message sent the day before can solve half the problem: name the likely conditions, suggest suitable shoes or layers, and explain where guests should arrive.
Keep one lovely rainy-day detail
A backup should feel like part of the wedding, not a storage room you reluctantly entered. Move one important arrangement, a line of candles or the ceremony backdrop into the covered setting.
Then let the weather witchery remain what it should be: a free piece of ceremony alongside a sound plan. Ask for the clearing, pack the umbrellas and know that neither choice cancels the other.