Time to start thinking about winter.

Not only did the temperature fall to below freezing in parts of the Philadelphia area Monday morning, the National Weather Service used the S-word for the first time since the autumn equinox.

Of course, things could change between now and then, but the weather service says there’s a chance of snow Thursday night into Friday morning north and west of the city.

But that chance comes with a fair amount of uncertainty, as competing atmospheric forces could make or break the forecast. It is, once again, a time-will-tell sort of thing.

And as of Tuesday morning, it appeared any snow that will fall will be at some distance from the city.

Any snow that falls also will not linger, as the projected high temperature for Friday is in the 40s.

In the meantime, the weather service says, “mostly tranquil conditions are expected” leading up to Thursday night.

For the record, the earliest measurable snowfall in the Philadelphia area occurred on Oct. 10, 1979, when 2.1 inches fell on still-leafy trees, snapping branches and taking down power lines.