Wind chill advisory from 9 p.m. tonight until 9 a.m. tomorrow as the chill factor falls to zero to minus-10 *

An impressively strong Arctic air mass is sprawled over the eastern two-thirds of the country ahead of the last night of 2017. In the metro region, temperatures failed to break out of the low 20s, which combined with gusty winds out of the northwest (15-25 mph) to create wind chills in the single digits. It was the coldest December day in Washington since Dec. 24, 1989, as the official high at Reagan National Airport stalled at 23 degrees.

Wind chill values will stay dangerously low through tonight, including the all-important midnight hour. So make sure you bundle up if you plan to be outside. And Happy New Year!

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Through tonight: A bitter cold last night of 2017. A slight chance (20 percent) of stray snow showers in the early evening, especially south of the city. Otherwise, the main story line tonight will be the cold temperatures and low wind chills. Temperatures will be in the teens at midnight, including in the city, with a wind chill in the low single digits. Overnight lows will range from 7 to 12 degrees. Winds from the northwest at 10-15 mph will keep wind chills at or below 0.

View the current weather conditions at The Washington Post.

Happy New Year, and bundle up! George Jiang via Flickr

New Year’s Day (Monday): Out with the old, in with the cold. 2018 starts like 2017 ended, with really cold temperatures and brisk winds. Mostly sunny skies won’t help the temperatures much, with afternoon highs topping out in the low 20s. A cold wind from the northwest at 10-15 mph will keep the wind chill in the single digits again. Clear and cold tomorrow night with low temps in the single digits to low teens and a negative wind chill.

See Brian Jackson’s forecast through the week. And if you haven’t already, join us on Facebook and follow us on Twitter and Instagram. For related traffic news, check out Dr. Gridlock.

Impressive December cold outbreak: It’s not hard to quantify how anomalously long and potent the nearly nationwide cold spell has been over the past week. Records are dropping all over, including records for the longevity of the cold streak. Places such as Boston are on track to break the longest stretch of below-20-degrees days in its recorded history. And many records for daily lows continue to be broken, mostly in the upper Midwest and New England.

And if you need any proof to justify the use of the word “Arctic” to describe this cold-air outbreak, check out the source region of the Washington air mass over the past eight days. That’s a funnel of cold air being piped down straight from the Arctic Circle. Stay warm and happy in 2018!

NOAA depiction of the current air mass trajectory over the past 8 days. Our current air mass originated in the Arctic.

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