Flooding along vulnerable riverfront roads has been reported in Mercer county.

UPDATE as of 4:30 p.m. Monday...

Water level forecast for the Delaware River at Trenton, as of Monday late afternoon. (NOAA / AHPS)

As expected, the river leveled off just barely into the "minor flooding" category - enough to necessitate closing the southbound lanes of Route 29 and some local streets and ramps early today.

Latest guidance shows the river will hold steady for the next day or so, before slowly dropping by midweek. The Flood Warning has been extended through at least Tuesday afternoon.

Tuesday is a very busy day in Trenton, with the inauguration of Governor-elect Murphy. So any residual flooding troubles could turn into a big problem.

ORIGINAL POST from 8 a.m. Monday...

The icy Delaware River on Sunday. (Robert Lehman)

While last week's "January thaw" was a wonderfully welcome break from the arctic chill, the thaw-melt cycle does have a potentially hazardous side effect. Significant melt occurred along New Jersey's frozen waterways, sending broken ice chunks floating downstream. As the ice gets stuck on bridges, banks, and other such icebergs, it forms an "ice jam" that causes water to back up significantly upstream.

That's the exact situation we're facing on the Delaware River near Trenton on this Monday morning. According to the Middle Atlantic River Forecast Center, water levels surged from 13 feet to almost 20 feet overnight. That pushes the river into the "minor flooding" category.

River gauge forecast for the Delaware River at Trenton, showing a rapid rise starting Sunday night. (NOAA / AHPS)

Minor ice jam flooding is not uncommon along the Mercer County stretch of the Delaware, and last occurred in January 2014. According to Jill Myra, New Jersey Traffic South, the southbound lanes and riverside ramps of Route 29 from Trenton to Ewing Township can be particularly impacted by high water levels. In fact, as of this writing, Route 29 southbound has been closed between Calhoun St. and Market St. due to flooding and icy conditions. Myra reports traffic conditions have not been significantly impacted by the closure, as NJ state offices are closed Monday, in observance of Martin Luther King Jr. Day.

The National Weather Service has issued a Flood Warning for the Delaware River in southwestern Mercer County until 5:30 p.m. Monday. River models suggest the water has almost crested, and will slowly begin to subside by late-day Monday. For now, no impacts are expected further upstream.

Until then, remember to obey all road closures and police instructions, and never drive, walk, or swim through flooded areas.

Dan Zarrow is Chief Meteorologist and Chief Hydrologist for Townsquare Media New Jersey. Follow him on Facebook or Twitter for the latest forecast and realtime weather updates.