UPDATE 12/6/19, 7:40 p.m. — State Route 128 is now open. The road had been closed from mile marker 12 (just west of Navarro) to SR-1 due to the flooding of the Navarro River.
MENDOCINO Co., 12/6/19 — State Route 128 has been closed, from State Route 1 to 12 miles east of the 1, or just west of Navarro, due to the flooding of the Navarro River. There is no estimated time of opening.
This situation occurs often early in the rain year, before the river has a chance to breach the sandbar that develops at its mouth.
The river hasn’t flooded much, and is currently at 3.89 ft, but because the highway runs very close to the riverbank, that small rise can be enough to flood it.
Here is a graph of the river’s rise, with a projection for its continued growth, from the NOAA — they expect it to crest on Saturday.
Here is the tweet from CalTrans: