Washington DC Breaks All-Time Temperature For December 18th By Seven Degrees - WP [View All]

Records fell across the Washington region yesterday on an unusually warm December day that pushed the mercury to 76 degrees at Dulles International Airport, torching the previous high of 69 set in 1984. It reached 74 degrees at Reagan National Airport and 72 degrees at Baltimore-Washington International Thurgood Marshall Airport, also records.

Yesterday's warmth was the result of a high-pressure system over the mid-Atlantic that has kept cold weather at bay for most of December, according to Calvin Meadows of the National Weather Service in Sterling.

"We're in an El Niño year, a weather pattern where we get abnormally warm temperatures over the eastern Pacific Ocean," he said. "So we get stagnant low pressure off the West Coast, and consequently we get high pressure over the eastern United States, which keeps colder air away that would normally be starting to get down here. Hence, the milder temperatures of the past few weeks."

On average, daily highs this month have been 3.6 degrees above the norm, he said.

EDIT

http://www.washingtonpost.com/wp-dyn/content/article/2006/12/18/AR2006121801148.html