Chilling Halloween Forecast: Bay Area Braces for Coldest Week Since May

Gorilla costumes. Fleece-lined tights under a Poison Ivy costume. A yellow overcoat and long black wig mirroring Demi Moore’s character from The Substance. These options might keep ghouls and goblins warm on Halloween night.

The National Weather Service reports this week will be the Bay Area’s coldest stretch of days since May, with nighttime lows in the 40s in some locations on All Hallows’ Eve.

“You might have to put a jacket over the Spider-Man costume this year,” said Dylan Flynn, a meteorologist with the weather service’s Bay Area office. “Some places will see their first 30-something-degree morning since about May.”

And it might not just be the cold trick-or-treaters will have to contend with. Flynn said a trio of storms will likely bring small amounts of rain across the Bay Area through Sunday as a strong cold front moves over the region from the Gulf of Alaska, dropping temperatures with a polar air mass. That will bring a 40% chance of rain on Halloween evening.

“We’re going to have some rain from San Jose north through the morning on Halloween,” Flynn said. “The good news is the probability of rain is decreasing through the day. But I can’t say that it will be dry for the trick-or-treaters.”

To beat the chill while knocking on doors for candy, bar-hopping or celebrating at an outdoor house party, costume designer Hester Michael of Hester’s Designs in the San Francisco Excelsior neighborhood cautions people to either pick a costume that’ll “keep you warm” or find a base layer to wear under a strappy fit.

“A gorilla suit might keep you warm,” she said. “I remember my mom having us wear sweaters under our costumes, and it was awful.”

So far this year, she’s created a yellow motorcycle look to mimic Kill Bill, a family of characters from the Hot Dog on a Stick mall stands and a Scream mask with kitten ears. She said on a cold night, people could get chilly even in complete get-ups and recommends “fuzzy lined tights that look like you’re wearing tights, or you can wear thermals as tops, leggings and bodysuits.”

Marty Van Der Vert, who owns the 38-year-old family-operated One Stop Party Shop in San Francisco’s Noe Valley neighborhood, doesn’t think “people are worried about” the cold or rain and will dress up however they want.

“They could use cloaks or capes to cover up,” she said. “I also have every mask from every movie you’ve ever seen. I’ve got [Michael Myers from] Halloween, but I think I only have some of those guys left. You name it. I have it.”

Over the next couple of days, Flynn said temperatures will peak in the 50s in most places.

“That’s pretty low for a high temperature, and then by the time the trick-or-treaters come out, it’s even going to be cooling off further,” he said.

“Last week, we were about five degrees above normal; this week, we’re going to be about ten degrees below normal,” Flynn said.