Temperatures will be dropping at night this post-holiday weekend and staying cold into next week, and there's an increased risk of dangerous sneaker waves at Bay Area beaches.

As we slide into the holiday season this weekend, temperatures are forecast to turn properly wintery around the Bay, at least in the overnight hours. San Francisco is expected to have a nighttime low temp of 47 degrees Saturday, while it could hit 42 in Oakland, and there are freeze and frost warnings being issued for inland parts of the North Bay.

Out in Concord, as the East Bay Times reports, a low of 36 is forecast on Sunday.

Meanwhile, daytime temperatures will remain balmy, in the mid-60s.

The National Weather Service has also put out a warning about dangerous sneaker waves from the Sonoma coast down to Monterey. The Beach Hazards Statement goes into effect at 10 p.m. tonight (Friday) and goes through 8 a.m. Sunday.

Northwest-facing beaches will likely be the most hazardous.

Sneaker waves are powerful waves that, combined with rip currents, can knock people off their feet and pull them out to sea. The waves can be preceded by 10 or 20 minutes of smaller waves, and then a larger wave can suddenly wash much further onto the beach and catch people unaware.

Sneaker waves have also been known to knock people off of rocks and piers.

Anyone going near a beach is advised to watch the waves from higher ground for at least 20 minutes before getting closer, and to never turn your back to the ocean.

The sneaker wave warning comes amid some astronomical high tides which occur at this time of year. Coastal flooding could occur this weekend as well, due to these tides.

Photo: Taisia Karaseva