US weather 2013: a respite from extremes, except in the West

If you were to pick a one-word description of general weather trends for the continental United States in 2013, "mellow" wouldn't be a bad one to choose, if numbers from the National Climatic Data Center (NCDC) are any indication.

To be sure, weather conditions throughout the year didn't spare everyone from weather-related disasters. But in an overview released Wednesday, the center reported that the number of billion-dollar weather disasters in 2013 dropped back to "normal" levels compared with previous years; the Atlantic hurricane season was notable for its unexpectedly low number of hurricanes; the number of tornadoes appears to have been the lowest since 1990; and with notable exceptions, relief came to much of the country that had been struggling with drought for the past two to three years.

In 2013, "we saw a relatively benign year, especially when compared to the really increased extremes we saw in 2011 and 2012," said Deke Arndt, who heads the NCDC's climate monitoring branch, at a press briefing Wednesday.

If nothing else, the figures point out the kind of annual variability that can occur even against the backdrop of a generally warming global climate. In 2012, the continental US posted its warmest year in the instrumental record, while 2013 finished in a tie with 1980 as the 37th warmest year on record.

Even the NCDC's Climate Extremes Index – which yields the percentage of the country affected by extreme weather – fell slightly below its long-term average, according to Jake Crouch, a scientist at the NCDC offices in Asheville, N.C., who, along with colleague Adam Smith, compiles these monthly and annual reports.

Still, since the 1990s, the annual index has registered above its long-term average more frequently than below it. "That wasn't necessarily the case before 1990," Mr. Crouch said at the briefing.

In the end, 2013 "becomes a piece of a larger puzzle," Mr. Arndt noted. "It doesn't fully prove or refute what we already known about climate change."

But for parts of the country, the year has been anything but mellow.

California, for example, posted its driest calendar year on record, two inches below the previous record low for rainfall, according to Arndt. That is "a pretty wide margin for a location that is typically as dry as California," he said.

For the year, precipitation was 32.5 percent of normal statewide, and conditions don't appear primed to improve.

The state is two-and-a-half months into its water year, which is keyed to the beginning of the state's rainy season in November. The snow pack in the Sierra Nevada range, California's alpine backbone and a vital reservoir for much of the thirsty state, is 25 percent of normal.

Last August, dry conditions nurtured the 225,000-acre Rim Fire, the third largest wildfire on record for the state. Its flames made their way into the back country of Yosemite National Park before firefighters finally brought the blaze under control.

Indeed, while much of the country previously covered by drought has seen conditions ease, in the western US the drought has worsened.

Moisture that might have gone to the Golden State instead was shipped to Alaska, thanks to a persistent ridge of high pressure off the West Coast that drove moisture and warmth into that state. Alaska posted its 10th warmest and third wettest year on record last year.

Elsewhere, Colorado experienced the most destructive wildfire in state history in June. The Black Forest fire destroyed more than 500 homes near Colorado Springs. Later in the year, record heavy rains triggered widespread floods along the easternmost slopes of the Rockies.

The event caused more than $1 billion in damage, placing it squarely on the list of billion-dollar weather disasters the NCDC compiles.

Overall the country saw seven billion-dollar events, five of which were related to severe weather and tornadoes, and one to drought and heat, in addition to Colorado's floods.

Even the Great Lakes, with their perpetual allure as sources of water for drier, farther-flung locations, came up short last year. Lakes Michigan and Huron reached record lows early in the year, while water levels in the rest of the lakes were below average.