How global warming has changed Wasington winters – The Washington Post
Here are five ways our winter has changed.
1. It’s warmer
Average temperatures between December and February — or meteorological winter — have warmed markedly over the past 150 years.
Nights are less frigid, afternoons are milder and there are fewer instances of record-setting, extreme cold. Moreover, our cold spells don’t last as long as they used to.
Back around 1900, Washington’s average winter temperature — blending daytime highs and nighttime lows — was around 35 degrees. Today it’s closer to 40.
2. It’s less snowy
The trend toward warmer temperatures has diminished snow prospects in an area that often rides the rain-snow line. The increase in average temperatures means more rainstorms and fewer snowstorms. And, when it snows, the flakes are having a harder time sticking. This is especially true early and late in the winter.
In the early 1900s one might expect a winter in Washington to deliver about two feet of snow. That average has declined to 13.7 inches.
The average number of days with at least one inch of snow each winter has fallen from about seven to four.
3. It’s shorter
As the frequency and amount of snow has dwindled, so has the number of days with snow reported on the ground. The number of days with snow cover has dipped from an average around 20 in 1900 to just 10 today.
A century ago, Washington’s snow season — defined as the length of time between its first and last inch of snow — was about 80 days. Now, it’s around 40 to 45 days.
The shorter snow season is tied to rising temperatures in December and March. The average temperature in both months has climbed about five degrees over the last century.
4. Springlike severe storms are increasing
During the winter months, it’s usually too cold for strong thunderstorms, which require warm, humid air.
But this seems to be changing. In recent years, unseasonably mild air is being drawn northward more frequently, especially in February. During the 1960s, areas within 100 miles of D.C. would see about five severe storm days during winter per decade. That number ballooned to around 15 such days in each of the past two decades.
5. More blockbuster snowstorms
Despite our warming climate and trend toward less snow overall, five of Washington’s 10 largest snowstorms have occurred since 1996 in records that date to 1888. There are a number of theories why we might be seeing more big snowstorms, including global warming adding more moisture to the atmosphere and stronger coastal storms because of warmer Atlantic waters.
The winters of Washington’s future
In a world that continues to warm, Washington’s winters are projected to become even milder. Climate projections funded by the National Oceanic and Atmospheric Administration for the District indicate that by 2050 there will be two to three fewer days each winter in which the high temperature is below freezing. And the average low temperature is predicted to rise from around 30 to 32 degrees.
The federal government’s National Climate Assessment concluded that the ongoing trend toward a shorter snow season should continue. It also calls for the rain-snow transition zone to continue shifting north, meaning even more winter precipitation falling as rain.