Look at wind speed and temperature too
Rain is not the only variable that could derail your plan. Extreme heat or cold would also make your wedding be remembered for all the wrong reasons.
And finally, your wedding stylist would have to adjust your floristry and decor plans based on the predicted wind speed. We don't want things flying everywhere! If it does go above a certain threshold, then it simply become unsafe to proceed.
Read the meteorological data, not just your phone's weather app
Jump on sites like Weatherzone or Accuweather for a more accurate forecast. They also offer a deeper insight than just "is it going to rain or not."
One key metric when looking at precipitation is the volume of rain. Your wedding planner would be able to help you interpret what 1mm of rain look like vs 3 mm, and whether your plans could go ahead.
Location, location, location
Even without weather concerns, you should be aware of the logistical details of your chosen location. How far away is the nearest parking/car drop off spot? Are there bathrooms, or would you need to arrange a port-a-loo? What is the foot traffic around the space like?
