Extreme weather buried and burned Washington in 2010

Monday, January 3, 2011; 10:11 PM

From winter's paralyzing snowstorms to the searing heat and violent thunderstorms of the summer and fall, 2010 may have no match for severe weather in Washington.

After 2009 closed with a record snowy December, practically unimaginable amounts of snow descended on the region in early February. The 28.6 inches that fell from Feb. 5 to 10 in back-to-back storms was the most snow on record over such a short period. Although almost no snow fell after mid-February, the winter of 2009-2010 set a seasonal snowfall record of 56.1 inches, besting the old record of 54.4 inches in 1898-1899.

The spring was rather tame and unseasonably mild. For the first time on record, a freeze was not recorded in March in Washington, and astronomical spring (March 20 through June 21) was the warmest on record.

But the spring's relative warmth was nothing compared with the blistering heat that continued through September. Washington had its hottest June on record, and then tied for its hottest July. August was hotter than average (the ninth-hottest on record), but several cold fronts, which triggered damaging thunderstorms, brought episodic relief. In September, a heat wave produced the hottest day so late in the season when it hit 99 on the 24th. The summer was the hottest on record, and 2010 tied 1980 for having the most days - 67 - at or above 90 degrees.

Temperatures remained above average through fall. Washington's first freeze of the season did not occur until Nov. 29. As the last freeze occurred on Feb. 27, the days in between represented the second-longest freeze-free period on record.

The region mostly caught a break from hurricane-related extreme weather. Although the hurricane season tied for the third most active in the Atlantic, no storms directly affected the region. However, a deep plume of tropical moisture generated 4.7 inches of rain Sept. 30, resulting in the third-wettest September day on record.

After nine consecutive warmer-than-average months, the pattern reversed in December. Overall, the month was the 28th- coldest on record.

After such a warm but volatile year, questions arise about whether such weather extremes will continue into the future. As long-term temperatures have shown an increasing trend, probably linked to urbanization and the buildup of greenhouse gases in the atmosphere, the odds of warmer weather have increased. And warmer temperatures tend to increase the frequency and intensity of heavy precipitation events.

But when it comes to the record snowfall of 2009-2010, that was probably a unique event linked mostly to the combination of two natural weather patterns, a strong El Nino and an unusually strong negative phase of the North Atlantic Oscillation (NAO). A strong El Nino typically transports abundant moisture to the southeastern United States and enhances the odds for East Coast storms, while a negative NAO brings the cold air needed for snow from Arctic regions into eastern North America. Some researchers think they have identified a link between climate change and the tendency for a negative NAO, but such a link is the subject of debate in the scientific community.

As for the immediate future, because the NAO is once again trending negative, we expect colder-than-average conditions at least through the middle of the month. But this year, we have La Nina instead of El Nino, which tends to reduce snowfall. So bet on cold and dry weather, while knowing that with weather, little is ever certain.

The Capital Weather Gang's Ian Livingston contributed to this report.

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