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Abnormally warm weather to dominate Lower 48 through winter solstice

Temperatures are set to rise 10 to 20 degrees above average for an extended time

(NWS)

Winter technically starts on Dec. 21 but, for the two weeks leading up to it, it will feel more like spring across much of the United States. The central and eastern Lower 48 are in line for an extended period of unseasonable warmth.

The National Weather Service’s Climate Prediction Center is projecting high chances of above-average temperatures for the eastern two-thirds of the nation both six to 10 and eight to 14 days into the future.

The core of the warmth in the eight-to-14-day outlook is centered over the mid-South, Tennessee and Ohio valleys, southern Great Lakes and interior Mid-Atlantic, where there’s a 90 to 100 percent chance of above-average temperatures. In other words, unusually mild weather is virtually a lock. According to Brian Brettschneider, a climatologist and researcher in Alaska, the Climate Prediction Center hasn’t been this confident in such extensive warmth eight to 14 days into the future since 2015.

The predicted warmth builds on record-setting high temperatures that kicked off December across large parts of the Lower 48 states. Four states tied or established record highs for the month last week. A brief blast of cold air is displacing the warmth for a few days this week but will not last.

This week’s warmth

The week got off to a warm start on Monday when temperatures climbed 20 degrees above average along the Eastern Seaboard ahead of a strong cold front that brought tornadoes to Tennessee. Washington, D.C., hit 70 on Monday before dropping 14 degrees in an hour as the cold front blew through, with winds gusting to 49 mph. Average highs in the nation’s capital this time of year hover around 51 degrees. Baltimore also made it to 70, while Philadelphia climbed to 67 degrees and New York to 61.

Parts of the Mid-Atlantic are expected to receive some festive snowflakes Wednesday before temperatures spike above 70 degrees once again on Saturday ahead of a front. That warmth is already gathering across the Plains and will sweep east over the coming days.

Oklahoma City is expected to hit 72 degrees on Thursday and 76 on Friday, which would break a daily record that has stood since 1996. The Sooner State’s capital is ordinarily in the lower 50s this time of year. Highs will fall back into the upper 40s on Saturday before a warm-up early next week.

Dallas-Fort Worth will flirt with records, too, as highs climb into the 80s later this week. Friday’s number to beat for a record is 84 degrees, which is in reach but may be a bit of a stretch. That record was set back in 1938. The forecast is for highs a solid 20 to 25 degrees higher than the upper 50s that are more characteristic of mid-December.

Next week’s warmth

The warmth will be squashed east into Saturday, with the day beginning 30 degrees above average from the Midwest eastward. Temperatures will drop 20 degrees or more in just a few hours along the front, but they won’t stay low for long.

Weather models depict another surge of top-tier warmth becoming established over the center of the county early next week. Any periodic cool-downs will be tepid and fleeting.

Some modeling suggests that the intensity of the next week’s zone of high pressure or “heat dome” supporting the mild weather could be historic for the time of year.

Temperatures next week could average 10 to 20 degrees above normal east of the Rockies. Here’s what this might mean for high temperatures most days next week:

  • Dallas: Highs in the 70s
  • Oklahoma City: Highs in the 60s to near 70.
  • Chicago: Highs in the 50s to near 60.
  • Atlanta and Nashville: Highs in the 60s
  • Washington: Highs in the 50s and 60s
  • New York: Highs in the 50s
  • Boston: Highs near 50

What’s behind the warmth?

A number of factors are conspiring to yield the enduring above-average temperatures. High pressure south of the Aleutian Islands in the Pacific near the international date line has been responsible for a dip in the jet stream offshore of the West Coast between Alaska and Hawaii, where it has been quite stormy. That, in turn, allows the jet stream to slice northeastward over the Northern Rockies and Upper Midwest, permitting warmth to build to its south.

It also enhances the southwesterly component of winds over much of the central United States, resulting in downsloping, or the forcing of air down the mountains — in this case the Continental Divide and Rockies. That leads to warming and drying, which in a sense is a self-reinforcing process. It’s no wonder the Plains have been warm to borderline hot.

The effects of human-induced climate change are also playing a role, tipping the scales toward warmth. In the absence of human influence, heat extremes and cold extremes would remain roughly balanced. Instead, a 2.5-to-1 ratio of daily hot versus cold records has been observed in the United States this year — 30,511 to 12,177, to be exact.

That preferential tendency toward heat extremes becomes even more marked globally, particularly when comparing all-time records. So far this year, 704 record high maximum temperatures have been recorded worldwide, and only 134 record lows. That’s more than a 5-to-1 ratio.

As the Earth continues to warm because of human activities, late-season heat and bizarre winter warm-ups will become increasingly common and greater in magnitude.

The Climate Prediction Center favors above-average temperatures sticking around in the central and eastern United States for most of winter, although occasional incursions of cold air should still be expected.

Jason Samenow contributed to this report.

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