Peter Becraft, associate winemaker at Anthony Road Wine Company sent me this shot this morning, saying that:

"We are cold stabilizing a tank of red, which is pretty easy to do when
it is 18 degrees and colder outside.  This particular tank always tends
to drip small drops from the manhole seal when the temp gets down
there.  What you are seeing is a slow accumulation of drips over a
couple of chilly days and nights.  No need for alarm."

And if you're curious, that's Tony's Red, a semi-sweet red made mostly of Rougeon.