Some very cold air is descending on the Bay Area this week ahead of another storm system, and all signs point to Tuesday morning likely being the chilliest that San Francisco has seen in four years.

The mercury hasn't hit 39 degrees in the city since January 6, 2017, according to the National Weather Service's Bay Area bureau, but it may do so again tomorrow morning and hit freezing temperatures of 32 or below across the North Bay at the same time. For much of the country, this kind of winter chill is child's play, and 39 is practically shorts weather in Chicago. But here in the Bay Area, that is FREEZING and you will likely see a lot of social media posts to that effect tomorrow.

The high on Tuesday will still be a usual, temperate-SF 49 or 50 degrees. But you might see more low lows on more mornings this week, so perhaps crank up the heat or pull out an extra blanket to throw on the bed.

Meanwhile, the rain continues, and it was especially heavy in the South Bay Monday morning. Expect more rain through Wednesday in SF, with Thursday bringing the first break in what feels like forever. Friday and the New Year's weekend will be sunny and chill — and the mornings will be especially cold, still, with the Weather Channel predicting a low of 38 degrees on Saturday morning.

And Tahoe has seen incredible amounts of snow in the last week, and it's still not letting up. A 70-mile stretch of I-80 through the Sierra was shut down to traffic for most of the weekend and into today, and other roads were closed as well due to white-out conditions.

As Tahoe ski expert Kevin "Coop" Cooper tells KTVU, "This is probably the most snow that I’ve seen in a single system in quite some time, we’re talking over a decade." There are reports of 10-foot snow drifts and piles in driveways, and it's already being called "The Blizzard of '21."

And as Cooper writes on Twitter today, "With the roads closed, neighborhoods unplowed and another day of wind, and snow fall ahead, its time to hunker down, shovel out, and get yourself ready to kick off 2022 with our snowpack well over 190% for the month of Dec."

Photo: Osman Rana