The calendar is fully in 2016, but the rains that closed out 2015 in the Midwest continue to leave an indelible mark on the region’s rivers. A torrent of water has worked down the Mississippi River, breaking winter flood records and inundating communities along the river and its tributaries.

Rivers are cresting at or near record height across the Mississippi and Ohio River Valleys. Nearly a dozen locations have already set all-time record high water marks. In St. Louis, the river set a winter high water mark on Friday with cresting at 42.58 feet on Friday. That’s also the third-highest flood level on record.

The previous winter record holder is December 1982, when the river reached 39.27 feet. Perhaps not coincidentally, that was also during a strong El Niño, which tends to amp up precipitation in the region.

Memphis is the next city in line for flooding. The crest should reach the city by the end of the week, though rising waters are already having an impact.

By next week, floodwaters will reach New Orleans and the Army Corps of Engineers is creating a flood emergency plan to open spillways into Lake Pontchartrain if needed so rising waters don’t inundate the Crescent City.

The timing is unusual — and warm weather played a major role. The Midwest is no stranger to river floods. But they usually happen in springtime after upriver snows melt, which send water streaming toward the Gulf of Mexico. Of the 133 times that the Mississippi has reached flood level in St. Louis, more than half have occurred during the spring while only three have occurred during winter.

While El Niño might be helping bring the rains, what really helped kicked the floods into overdrive is the warm end to 2015. Temperatures were above freezing for much of the Midwest at the tail end of the year, so much of the precipitation that fell the last week of December was rain rather than snow. Up to 12 inches of rain fell over three days from Oklahoma to Illinois, setting up rivers for this unusual winter flood event.

Mississippi River flood before and after

Satellite images showing Mississippi River flooding in early 2016 vs. normal river levels for early January.

“While major flood events in the Midwest and the Mississippi Valley are not unusual, the fact that we had such extraordinary flooding in late December is certainly one for the record books,” Steve Bowen, a meteorologist at re-insurer Aon Benfield, said.

The Midwest has seen catastrophic flooding as recently as spring 2011 when the Mississippi and Missouri rivers set a number of records. In an odd twist of fate, the tropical Pacific also played a role, though it was due to El Niño’s opposite phase, La Niña. That helped drive a cold, snowy winter in the northern stretches of the rivers’ basins, which fueled a massive runoff in spring.

The damage could top $1 billion. The flood is expected to continue into at least next week, but the financial toll it has taken already is clear.

“The Mississippi River flood event is pretty much a certainty to be a billion-dollar event. That is based on current damage. The scope of impacts to residential, commercial and agricultural interests has been pretty substantial,” Bowen said. “Despite many communities taking flood protection measures following historic events in 1993, 2008, 2011, the current event still managed to have a tremendous footprint — and it’s not over yet!”

You could call it the first billion-dollar disaster of 2016, but because the rains fell in 2015, Bowen said he’s counting this as 2015’s penultimate billion-dollar disaster. Either way, the flood is the latest in a string of odd weather to kick off winter.