Drivers in the Northland should be ready for possible closed roads over the next couple of days as steady rain combined with frozen culverts makes flooding a possibility, transportation officials say.

That could include the tunnels on Interstate 35 in Duluth.

“We typically do have problems in the tunnels,” said Beth Petrowske, spokeswoman for the Minnesota Department of Transportation. “We did quite a bit of work in the tunnels last year, so we’re hoping maybe it isn’t as bad as it has been in the past. But we really won’t know until it starts raining.”

Much of the Northland is under a flood watch from this afternoon through Thursday evening because of rainfall expected to total from 1 to 1½ inches, mild conditions and the 25 inches of snow on the ground with no place to go. From 4 to 8 inches of snow are likely in northwestern Koochiching County, where the National Weather Service posted a winter storm watch.

If there is flooding, it is not expected to be in the form of rivers and streams rising beyond flood level, said Steve Gohde, a hydrologist for the National Weather Service in Duluth.

It will be more of an urban variety.

“We expect that there’s going to be sluggish drains because of snow and ice … so there’ll be areas of street flooding and ponding,” he said. “Our road crews, I think, caught the message early and have been working hard to mitigate that situation.”

St. Louis County is prepared to do that by freeing blocked culverts with culvert steamers, engineering and maintenance supervisor Ross Benedict said in a news release.

The devices use a hose and high pressure to spray hot water at blocked culverts. The nozzle of the hose can be pulled through the ice to create a water through which water can drain.

The county had culvert steamers when he first came on the job 40 years ago, Benedict said over the phone, but today’s units are much more sophisticated. They’re used throughout the winter and into the spring, but this situation is slightly unusual.

“We don’t expect to get an inch of rain when there’s this much snow, but we do expect culverts to freeze up,” Benedict said.

The county also will have crews ready to post signs warning if roads are closed or if they’re open but have water on them, according to the news release.

MnDOT crews also have been at work thawing culverts, Petrowske said. But flooding still may occur, and in that event lanes or sections of highways may need to be closed.

Driving through standing or moving water is dangerous, and it’s illegal to drive through areas that are barricaded, MnDOT reminded motorists in a news release.

Tuesday evening, the city of Duluth had already announced the closure of a portion of 88th Avenue West near Grand Avenue due to water on the road from a nearby creek, leaving Idaho Street as the only entrance to the Morgan Park neighborhood.

Expected conditions also might affect homeowners.

Water dripping off houses will encounter frozen ground and might find ways into the house that “aren’t usual,” Gohde said. “So we’re advising people to be keen to the status of their sump pumps.”

The existing snow contains the equivalent of 5 inches of moisture, Gohde said. If the predicted rain comes, that will grow to 6 inches.

“Of course, on sloped roofs, some of that water is going to be running off, but much of that water will remain in the snow, and that will drastically increase the weight,” he said.

Roof collapse is a possibility, according to the weather service, especially on barns and outbuildings.

The next problem could occur toward the weekend, Gohde said, when somewhat colder conditions could cause secondary roads and streets to become icy and slippery.

High temperatures today and Thursday are expected to be in the low 40s.