National Weather Service forecasters say the warmest day is going to be Christmas Eve, with forecast highs of 61 degrees in Portland, Maine, 62 degrees in Concord, New Hampshire and 63 degrees in Burlington, Vermont.

The current record for that date is 53 in Portland, 57 in Concord and 51 in Burlington.

Forecasters say all three cities also are on tap to break records for warmth for the entire month. Burlington is running 7 degrees above the current record and Portland and Concord are running a degree or so ahead of their records.

A weather pattern partly linked with El Nino has turned winter upside-down across the U.S. during a week of heavy holiday travel, bringing spring-like warmth to the Northeast, a risk of tornadoes in the South and so much snow across the West that even skiing slopes have been overwhelmed.

In a reversal of a typical Christmas, forecasters expect New York to be in the mid-60s on the holiday — several degrees higher than Los Angeles.

Big parts of the county are basking in above-average temperatures, especially east of the Mississippi and across the Northern Plains. Record warmth was expected on Christmas Eve along the East Coast,  said Bob Oravec, lead forecaster with the National Weather Service.

He laid the credit — or blame — with a strong El Nino pattern, the warming of surface waters in the Pacific Ocean near the equator. That’s helped drive warm air west to east across the Lower 48 and kept colder air from the Arctic at bay, he said.

Elsewhere, severe thunderstorms and possible tornadoes were forecast for Wednesday in northern Alabama, northern Mississippi, Arkansas and western Tennessee. Tornadoes are not unheard-of in the region in late December, but the extreme weather, driven by warm temperatures and large amounts of moisture in the atmosphere, was nonetheless striking, said Jeff Masters, director of meteorology at Weather Underground.

In addition to El Nino, a weather pattern called the North Atlantic Oscillation is also helping keep cold air bottled up in the Arctic. Combine that with warm temperatures around the planet from man-made global warming, he said, and you have a recipe for intense weather: “There are a couple of natural patterns at work, and then there’s this human-caused component too.”