wpostServer: http://css.washingtonpost.com/wpost

The Post Most: Local

Posted at 10:30 AM ET, 11/19/2012

Does a cold November into December mean a cold winter? An extreme example of the opposite

Temperatures so far this month have averaged 4 degrees below average in Washington, D.C. Around this time of year, especially when cold weather occurs, we often hear people say something like, “If it’s this cold now, how much worse will the rest of the winter be?” It’s a natural knee-jerk, calendar-based reaction, corresponding with the old adage, “As the days lengthen, the cold strengthens.”

No one is disputing the fact that overall winter weather patterns are affected—and even controlled-- by the broad hemispheric game-changers such as El Niño/La Niña, the NAO (North Atlantic Oscillation), and the PDO (Pacific Decadal Oscillation).

Based on a careful analysis of all these systems, a tentative winter outlook is ventured by most weather media, such as the Capital Weather Gang. But we pointed out, the nature/strength of some of these game-changers cannot be predicted very far in advance. Thus the dilemma: will the late fall winter pattern last throughout much of the winter?

As a weather speaker, when this question arises, I often like to refer to the winter of 1989-90 as a prime example of the kind of radical reversal that can occur in North American mid-winter weather patterns.

While November 1989 began on the mild side in the South and West and somewhat cooler than average elsewhere, starting in late November 1989 and through most of December, the weather changed drastically. It became brutally cold and snowy east of the Rockies, with the greatest departures east of the Mississippi, particularly around the Great Lakes states, where temperatures were as much as 18 degrees F below normal. At the time, it was the fourth coldest December* in almost 100 years.

Related: December 1989′s Epic Cold (Ryan Hanrahan)

In the D.C. area, the average December temperature at DCA (Reagan National Airport) was 27.9 degrees F—almost 12 degrees below DCA’s current December average and the coldest December since 1876. (Even December 1917, one of the most frigid Decembers—and winters-- of all time in Washington and in the East, managed to only tie December 1989 with a 27.9 degree F average temperature. However, temperatures did fall to -13 degrees F toward the end of December 1917.)

The 1989-90 winter started off with a bang here! Following 3.5”of relatively powdery snow, Washington was “treated” to a rare white Thanksgiving. After that, several small snow events maintained the snow cover until Christmas, when 2” of snow remained. It may have been the only time since official records began that a white Thanksgiving and a white Christmas occurred in the same year here. Some of you weather buffs may be able to correct me on this.

Perhaps the highlight of that frigid December in the East was not here but in the coastal Carolinas, where a record-breaking pre-Christmas blizzard occurred December 23-24. It provided a rare winter wonderland to such unlikely locations as Wilmington, NC (15”), Cape Hatteras, NC (13.3”), and Manteo, NC (10”). The storm, which stayed far enough offshore to give barely 1” of snow to coastal Virginia, produced 60 mph winds and snowdrifts as high as 4-8 feet all along the affected part of the NC coastline.


Snow amounts during December 22-24 snowstorm in eastern North Carolina (NWS)

More from the National Weather Service office in Newport/Morehead City, NC:

Elsewhere, two inches of snow fell at Savannah, GA; one of only three times that snowfall in the city required a ruler for measurement. Charleston, SC picked up 3.9 inches. The storm resulted in the first white Christmas on record from northeastern Florida to North Carolina. Snow fell in Tampa and Daytona Beach as Florida experienced its most widespread snowstorm in history and their first white Christmas in history as airports and interstates were shut down. Snow and sleet fell as far south as a Sarasota to [the] Melbourne line. Many traffic accidents and several fatalities occurred on ice-covered roads in North Florida. In the wake of the storm, Christmas morning low temperatures along the coast set all-time low records in many locations. Wilmington reached zero degrees F. Jacksonville reached minus 5 degrees.

After Christmas, the entire circulation pattern changed, with the jet stream retreating far to the north. Whereas December 1989 was the fourth coldest December in almost 100 years nationwide and the coldest of the 20th Century in the East*, January 1990 turned out to be the warmest January since the 1895 beginning of national weather records**

The accompanying chart depicts average temperatures, as well as snowfall totals, in the local area for December 1989. And, for good measure, I’ve thrown in the winter of 1917-18.


December 1989-February 1990, December 1917-February 1918 average temps and snowfall
As discussed, during the winter of 1989-90, temperatures were far below normal for December but far above normal in January and February. But during the winter of 1917-18, temperatures were far below normal in both December and January and near normal in February.

As a footnote, since it’s well known that a negative NAO (North Atlantic Oscillation) correlates well with a cold (and often stormy) East, and vice versa, I looked back at that data. It turns out that during December 1989, the NAO was negative on 25 out of 31 days but during January 1990, the NAO was in a positive phase on 27 of 31 days.

*Weatherwise, February 1990

**Weatherwise, April 1990

By  |  10:30 AM ET, 11/19/2012

Categories:  Latest, Lipman, History

 
Read what others are saying
     

    © 2011 The Washington Post Company