Cold weather is moving into northwestern New Jersey fast, and it is about to hit plants and pipes. A freeze warning is in effect for part of the state tonight.

The National Weather Service has the warning covering Hunterdon, Morris, Sussex, Warren and western Passaic counties. It starts after midnight tonight and runs until 9 a.m. Sunday, Oct. 18.

Temperatures in those counties could drop to around 30 degrees. That is cold enough to kill plants and damage outdoor plumbing, so anyone with gardens or exposed pipes has a reason to pay attention tonight.

Saturday is expected to stay raw, with the chill sticking around before the overnight drop arrives.

The forecast comes as a nor'easter threat is growing in the region. Nor'easters are not common, but they tend to show up in clusters. Meteorologist Uccellini, who co-wrote a book on the storms, put it plainly: "One of the things we emphasized in the book is the episodic nature of these storms. They come in batches." Researchers counted only 47 storms that qualified as nor'easters between 1949 and 2003.