Amid the dismal rain this week, Kathy Purcell has been watching the sky, hoping for the sun to shine on her charity's benefit this weekend.

"We pray a lot," said Ms. Purcell, executive director of the Pittsburgh affiliate of Susan G. Komen for the Cure, which supports breast cancer research and education.

If it rains on "Paws for the Cure," the organization's dog-friendly walk at Hartwood Acres on Sunday, the more than 500 people expected at the event may have to walk in the rain, said Ms. Purcell.

But she's is still crossing her fingers for clear skies.

As many local charity organizations have learned, the fickle fall weather can be a blessing or a curse for outdoor benefits; a dreary day can easily persuade people to stay at home, warm and dry.

"We're always somewhat at the mercy of nature," said Jim Bonner, executive director of the Audubon Society of Western Pennsylvania.

Each year, some organizations get lucky, and others take a hit.

The Audubon Society schedules almost all of its events outside, and sometimes, said Mr. Bonner, Mother Nature "cashes the chips back in."

Mr. Bonner expected hundreds of families to swarm the Beechwood Farms Nature Reserve for the Audubon Society's annual AppleJamm festival on Sept. 26, so he capped the event at 1,200 attendees, arranged for three off-site parking locations and hired shuttle buses.

Then it rained, hard. The festival that attracted 1,900 last year drew just 200 people, and, according Mr. Bonner, the Audubon Society lost more than $1,500.

When it rained on the Bridgeville Peddler Days, a fair for artists, crafters and fundraisers on Oct. 9 and 10, Midge Gilson, who organized the event, said she had to make the most of it.

"We were able to set up underneath a building," said Ms. Gilson. But she said the rainy weather discouraged many people from attending the fair, which benefited the Bridgeville Historical Society and the Bridgeville Public Library.

"A lot of people didn't even show up," she said.

Some organizations hope to avoid such a fate with detailed rain plans.

Sam Capezzuto, director of the Fern Hollow Nature Center in Sewickley, took a practical view.

The Nature Center is hosting an event called "The Great Pumpkin Spooktacular" on Oct. 24 to benefit environmental education for students in the area.

With stories and s'mores around a bonfire, a night hike and an outdoor movie screening, the schedule is hardly waterproof, but Ms. Capezzuto said that unless there is lightning, the event will not be canceled.

If it rains, the bonfire will move to a fireplace. The outdoor screen will come indoors. The hike will continue as planned.

"We tell people to come dressed for the weather," she said.

But a rain plan can only go so far. The Audubon Society had a rain plan for AppleJamm, but the festival still suffered.

A moon bounce activity had to be canceled because of insurance policy rules. Some vendors never showed up. Mr. Bonner said the cold, pervasive drizzle probably persuaded people who were waiting to see what the weather was like to stay home.

So while the Audubon Society had raised enough money at last year's AppleJamm to spend more than $27,000 on summer camp scholarships for 94 needy children, this year it will have to dig into last year's funds to keep the program alive.

To recoup their loss, the society is allowing people to come and build "scarecrows" out of materials left over from AppleJamm any time during the month of October for a $5 donation.

Proceeds will go into the scholarship fund -- insurance for a rainy day.

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