Authorities are monitoring the Snoqualmie, Snohomish and Skykomish rivers in Snohomish County and the Tolt River in King County, with rivers set to reach their highest level midday Wednesday.

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Steady rainfall and rising snow levels are triggering potentially major flooding in Snohomish and King county rivers, officials warned Tuesday.

Authorities are monitoring the Snoqualmie, Snohomish and Skykomish rivers in Snohomish County and the Tolt River in King, according to news releases.

The rivers were to reach their highest level midday Wednesday, said Dennis D’Amico, a meteorologist with the National Weather Service in Seattle.

The rising water likely will result in road closures in Snohomish County, said John Pennington, director of the county’s department of emergency management.

Homes near Monroe could also be affected, he said.

“This is kind of an unexpected event for this time of year … (and) it kind of came out of nowhere,” Pennington said.

“But we’re asking residents to be cognizant of rising waters.”

The water levels are not expected to approach record levels, however, Pennington said.

Meanwhile, the King County Flood Warning Center opened at 1:30 p.m. Tuesday.

By evening, the Tolt River had reached Stage 3 of a four-level flood alert system — signaling moderate flooding, according to an automated call left for residents.

Water levels on that river were expected to crest overnight Tuesday and drop below flood stage by Wednesday evening, D’Amico said.

The flood concerns hinge in part on whether persistent rain continues, Pennington said.

The latest forecast called for heavy rain throughout Tuesday night, but slowing precipitation and falling snow levels throughout Wednesday, D’Amico said.

Brian M. Rosenthal: 206-464-3195 or brosenthal@seattletimes.com. On Twitter @brianmrosenthal.