Event planner types: My outdoor public event has threat of rain. How do I deal?

Every year I hold a brief public historical commemoration ceremony in a park here in NYC. This year’s event is scheduled for Sunday. If the weather was good, I’d expect a crowd of 20 to 40 people and the whole thing would last about 30 minutes.

Unfortunately, the forecast predicts that Sunday will probably be wet. Exactly how rainy, and when the rain will start and stop is unclear according to the forecasts I’ve seen.

The event was publicized far and wide to the general public and press, with no pre-registration required, so I’m not dealing with a fixed, reachable set of possible attendees (although a portion of the people were notified through an email list I have). A rain date was included on most announcements. There is a “more info” phone number and a webpage associated with the event.

I’ve never had to deal with the possibility of rain before, so I need advice. I suspect there is a tried-and-true gameplan that event pros follow in these situations, and I’d love to hear it.

If the day is a total washout, I assume I’ll have no choice but to reschedule. I’ll put a message on the phone machine and website and send out a new wave of emails, right? And I’ll put up a sign or post a volunteer at the park to inform any diehards that still show up.

But what if it’s one of those ambiguous weather days that starts with sporadic showers and can go either way at event time (1:00p)? When do I decide if it’s a “go” or not. Do I bother to announce if it’s “on,” or just if it’s “off”? Any tips for handling the event itself, if it’s still a little misty/drizzly?

With all your answers, please bear in mind that this is a no-budget affair staffed by a few volunteers. I can’t order in giant tents, or hand out umbrellas or ponchos, or move the ceremony to a big hall or anything elaborate like that.

Thanks all, in advance.

Why not just have an instant set tent available? You can have the ceremony held under it and the guests will know to wear appropriate clothing and bring umbrellas, I would hope.

something like that, or if the budget permits, something larger that can hold the guests as well:

Of course, I missed the line that you can’t buy tents- Sorry about that. Clearly I need more coffee.

Consider buying some Pluvius insurance.