Much of the nation is in the grip of a fierce cold blast, but here in D.C., things haven’t been so bad. That’s about to change in a big way over the next week, with Sunday’s disruptive wintry mix and a punishing punch of polar air landing here by Tuesday.

As much as this December seems unusually cold – and it is, at this early stage – it could be worse. Some in the meteorology field are drawing comparisons to the early winter of 1983-84, which set a slew of cold records primarily over the Central U.S. and got bitterly cold in D.C. a week before Christmas. However, while the current and upcoming polar plunge shares similarities with the pattern from December 1983, there are enough differences to suggest that D.C. avoids the worst of this winter wickedness.

To be sure, temperatures are poised to drop 15-20 degrees below average during the middle of next week.


But, the magnitude of that cold anomaly (number of degrees below the average temperature) will be barely half of that which is currently in place over the western High Plains.

Temperature departures from normal on Thursday afternoon. Purple numbers represent the coldest departures. This same air mass - in modified form - will start to seep into our area on Saturday. (Penn State University e-WALL)
Temperature departures from normal on Thursday afternoon. Purple numbers represent the coldest departures. This same air mass – in modified form – will start to seep into our area on Saturday. (Penn State University e-WALL)

What’s behind the polar plunge?

One of the key drivers to the Arctic outbreak is a large upward bulge in the jet stream – what meteorologists call a ridge – over Alaska.

Water vapor imagery centered on Alaska from Thursday night. The black line represents the periphery of an upper-level ridge, and the arrows indicate counterclockwise flow around the ridge (area of high pressure). The two black Hs represent surface high pressure centers, which slide down the eastern periphery of the Alaskan ridge and deliver extremely cold air from the Polar region to Canada and the U.S. (NOAA Satellite Services Division; original image modified by Rick Grow)

Surface high-pressure areas, which contain frigid air, build over far northern Canada and slide down the eastern side of the Alaskan ridge, thanks to the southward movement of the jet stream. Stronger high-pressure cells pack colder air, and the very dense nature of Arctic air often means it will undercut and eventually replace an existing warm air mass. We will experience this locally on Sunday as cold, dense air sinks to the surface and warmer air “overruns” the surface, causing a wintry mix. The Arctic boundary will push through completely on Tuesday.

Sequence of images from top to bottom shows evolution of surface weather features over the next several days, as forecast by meteorologists with NOAA’s Weather Prediction Center (WPC). At top, note the 1050 mb high pressure over Alberta. Some of the associated cold air with that system will ooze into the Northeast and Mid-Atlantic into Sunday. The same front bringing us rain today (see the top map again) will drop into the South through Sunday morning (second map from top), but return back north as a warm front during the afternoon and evening, slowly changing our precipitation to plain rain from southeast to northwest. The front passes south of the region again on Tuesday (third map from top), making way for a stronger surge of cold air. Additional strong surface high pressures are in the pipeline over and east of Alaska next Thursday (bottom map), and they may direct another shot of cold air into the D.C. area toward the start of the third week of December. (NOAA WPC)

Now turn your attention to the forecast map for this afternoon (the top graphic above). Note that the pressure reading associated with the surface high over Alberta is near or slightly above 1050 mb. That is certainly high! It does not come close to the pressure measured on Christmas Eve 1983, however, in Miles City, Mont., which Wunderground’s Weather Historian Christopher Burt says set the record for highest pressure in the U.S. at 1064 mb.

Daily surface weather map analyzed on December 24, 1983. It’s difficult to see clearly, but note the isobar – or line of constant pressure – immediately surrounding the “HIGH” pressure center in Montana. That is the 1060 mb isobar. (NOAA Central Library Data Imaging Project)

Just how cold did it get in December 1983?

It was so cold around Christmastime in 1983 that Reagan National remained below freezing for 86 consecutive hours between December 23-27. The airport set record lows of 5 and 3 on Christmas Eve and Christmas, respectively. Dulles’ lows hovered around zero on the 24th (1), 25th (-2) and 26th (-1). As a whole, December 1983 was nearly four degrees below average (with a mean temperature of 36F).

More impressive record-setting cold plagued the Plains and parts of the Midwest that month. Amarillo recorded subzero lows on seven days mid-late month (the average low is 23 for that part of December) and set, in total, six daily low maximum temperatures and five daily minimum temperatures. On Christmas Eve 1983, Amarillo’s high/low showed little spread (2/-3).

Sioux Falls, S.D. set four daily low maximum temperature records, with the lowest high occurring on December 23, 1983 (-14). The average high on that date is 27, which meant that the town was an astounding 41 degrees colder than normal! According to Joe Sheehan of the National Weather Service Forecast Office (NWSFO) serving Sioux Falls, temperatures fell below zero on the night of December 15 and didn’t rise above zero again until Christmas. Also, according to Joe, a temperature of -22 in the early morning hours of Christmas Eve combined with average wind speeds of 30 mph combined to produce a wind chill temperature of -82. More can be read here.

Finally, in the midst of its coldest December on record at nearly 13.5 degrees below normal, Chicago sank to -25 on Christmas Eve 1983, a reading low enough for third coldest in the city’s recorded weather history. With wind speeds that morning ranging between 29 and 41 mph, the Windy City also experienced a wind chill temperature of -82, the coldest wind chill in Chicago’s recorded history. Highs remained well below zero for three consecutive days on the 23rd (-6), 24th (-11), and 25th (-5), each a daily cold maximum record. The NWSFO serving Chicago wrote more on this and other notable December weather events here.

How the current pattern is different from that in December 1983

A look at the upper levels of the atmosphere – around 18,000 feet above the surface, or at the 500 mb level – helps to explain why December 1983 was so cold nationwide. That same large ridge over Alaska responsible for the current and coming Arctic attack was a very prominent feature 30 years ago.

Reanalyses of upper air (top graphic) and temperature anomaly (bottom graphic) patterns in December 1983. The yellow,orange and red colors depict abnormally strong ridging and associated warmth over Alaska, while the blue and purple colors show a pronounced dip in the jet stream (or trough), as well as much below normal temperatures. The darker shades of purple reflect temperatures greater than 8 degrees colder than average. (NOAA/ESRL Physical Sciences Division)

The center of the upper-level high was situated midway between Alaska and Greenland early-mid month, but migrated south into mainland Alaska during the second half of December 1983. That southward realignment coincided with a crash in the Eastern Pacific Oscillation (EPO) index, an atmospheric signal that describes the pressure pattern over the central North Pacific and northeast Pacific basins. When the EPO index turns negative, a high-pressure ridge builds over the northeast Pacific and extends into Alaska; the jet stream dips well to the south across Canada and the Northern U.S.

Oftentimes, the anomalously cold air will spill over into the eastern U.S., though its duration is limited without a high-latitude blocking pattern in place. A negative phase of the Pacific North American (PNA) pattern, described by CWG’s Wes Junker as a pattern that favors a high-pressure ridge over the East and a storm track to the northwest, is a resisting force to the northern-based cold, and usually results in warm southerly flow and above normal temperatures here in D.C.

The PNA index was only slightly negative in December 1983 and, especially mid-late month, was absolutely overwhelmed by a flood of Arctic air downstream of the Alaskan ridge. Thirty years later, the PNA is trending more negative. It has been negative more often than not since late September.

Recorded measurement of the PNA index since mid-August (top) and forecast through mid-December (bottom). (NOAA Climate Prediction Center and NOAA/ESRL Physical Sciences Division)

What does this mean moving forward, beyond next week’s cold shot from Siberia, and another possible Arctic blast early during the week of December 16? Well, just as with anything in weather and climate, all factors should be considered and evaluated. Much of the latest ensemble model guidance features a westward shift in the ridge over Alaska to a position closer to Siberia. This shift appears to also draw the core of anomalously cold air westward, perhaps into British Columbia and Alberta. That may enable the warm ridge along and off the East Coast – beaten down temporarily by the cold shot next week – to exert more influence on D.C.’s weather toward the last third of the month.

Ensemble mean forecast at 500 mb for the December 12-19 period. This forecast shows the ridge shifting west toward Siberia. The coldest air relative to normal shifts west as well, into British Columbia and Alberta, and the response downstream may include warming temperatures over the East as the negative PNA signal becomes more relevant. (NOAA/ESRL Physical Sciences Division)

With so much cold air remaining in Canada, we will have to monitor the risk for colder interruptions. Anomalously cold spells would seem to be more likely across the northwest and north-central U.S. toward the last third of December, but the cold could slosh south and east from there at times. It’s important to state that an overall warmer-than-normal period – perhaps slightly so – would be susceptible to colder variability (highs in the 30s possibly). And if you time the colder air with a favorable storm track just right, then wintry precipitation events would remain in play.