It’s only Halloween, but winter is on the way.

Two storm systems moving out of the Gulf of Alaska are on track to bring the first substantial snow of the 2017-18 winter season to the Sierra Nevada, starting Friday, and widespread rainfall across the Bay Area over the weekend.

Have a comment about this? Join the conversation at our Facebook page.

Forecasters said Monday that gusty winds and 1 to 2 feet of snow are likely Saturday and Sunday along California’s main mountain passes, including Donner Pass near Lake Tahoe, Tioga Pass at Yosemite, Ebbetts Pass and Carson Pass, with perhaps a foot along the shoreline of Lake Tahoe this weekend.

“There’s a potential for chain requirements, travel delays and possible road closures.” said Chris Hintz, a meteorologist with the National Weather Service in Sacramento.

But fear not, trick-or-treaters. The weather should be dry for Halloween on Tuesday night, with temperatures in the 60s and low 70s in the afternoon and 60s and high 50s by early evening.

“Trick-or-treating in the Bay Area should be a piece of cake,” said Jan Null, a meteorologist with Golden Gate Weather Services in Saratoga. “It’s going to be a good mild, autumn day. No wind. No rain.”

The same storm systems that are forecast to turn the Sierra Nevada peaks white, and perhaps close higher-elevation mountain roads, are also expected to bring roughly half an inch of rain from Friday to Sunday in San Jose, up to 1 inch to San Francisco and the East Bay, and 1.5 inches or more to the Santa Cruz Mountains, Big Sur and the North Bay.

Reading this on your phone? Stay up to date with our free mobile app. Get it from the Apple app store or the Google Play store.

That’s raising concerns over the areas of Napa and Sonoma counties that are still recovering from this month’s historic fires.

“There’ s a potential for ash and debris flows in the areas that burned,” said Hintz. “If you get a lot of rain on a steep incline, that stuff can move. It can block drains and culverts and increase the risk of localized flooding.”

The season’s first big storm comes after record rainfall last winter ended California’s historic drought. For the ski industry, which suffered through four dry years between 2011 and 2015, a foot or two of snow the first week of November is the perfect Halloween treat.

“Everyone is getting really excited and gearing up,” said Michael Reitzell, president of the California Ski Industry Association. “If it’s a good normal season, this is about the time when we start to see the early snowfall and the temperatures drop so our resorts can begin snow-making.”

One resort already has opened, Mount Rose, about eight miles northeast of North Lake Tahoe in Nevada, which opened one run last weekend.

For weekend outings in the San Francisco Bay Area and beyond

follow us on Flipboard.

Mammoth Mountain and Boreal are scheduled to open Nov. 9. Squaw Valley, Northstar and Heavenly are scheduled to open Nov. 17. Kirkwood is planning to open Nov. 22, and most of the other 25 or so resorts in California should be open by Thanksgiving weekend.

Last winter, a relentless series of massive atmospheric river storms drenched California, flooding downtown San Jose along Coyote Creek, wrecking the spillway at Oroville Dam, washing out roads and bridges in Big Sur and ending the state’s historic drought.

That winter, which left many of the state’s reservoirs full or nearly full, brought in so much snow at times that Interstate 80 over Donner Pass closed several times. Firefighters at Lake Tahoe couldn’t find fire hydrants that were buried under 10 feet or more of snow. And big Sierra ski resorts closed more than once because so much snow fell in January and February that they couldn’t operate their chair lifts and other equipment.

“Last year was fantastic. We got an abundance of snow last year,” said Reitzell. “No one will ever complain about that, but there were a lot of operational challenges for the resorts and for people getting to the resorts.”

So much snow fell last year that people in shorts and bikinis were skiing at Squaw Valley over July 4 weekend. Mammoth Mountain was open for skiing into August.

Typically in November most of California’s ski resorts open only a few runs, mixing in natural snow with snow they create with large snow-making machines. As storms continue, they are able to open more runs and build a larger base.

Next weekend’s forecast snows — which prompted a special weather statement Monday from the National Weather Service advising that snow levels are likely to get down as low as 5,500 feet this weekend — might melt in lower elevations as the days warm up again. But a new storm system seems to be shaping up for the following week, forecasters said.

“It’s still a ways off, but there’s potential,” said Null.