The central and southwestern portions of the United States have experienced drought for the past several years. This photograph was taken in mid-February, 2010. By that point in winter, these rows would normally have been fully covered in snow. Photograph credit: Kristy Johnson (http://www.flickr.com/photos/kayaker1204/4359744393/
In spite of the massive blizzards that have slammed parts of the northeastern United States, much of the country is experiencing a pronounced lack of snow. And where there is snow, it is less than usual. It follows a very low snow year from the previous season, causing people to worry if low snowfall is the new normal.
A previous Icelights post, Arctic sea ice and U.S. weather
, discussed possible causes behind the changes in winter weather, trying to see if there are correlations to larger climate changes. Researchers like Jennifer Francis of Rutgers University are exploring the possibility that declining sea ice in the Arctic is altering atmospheric temperatures and weakening the jet stream. This change may shift the Northern Hemisphere storm track, leaving some places unusually snowy, or leaving normally snowy locations dry. Can a few good blizzards help reverse the snow drought across parts of the United States? Or is this string of dry winters yet another symptom of climate change?
The ebb and flow of snow
A lack of winter snow can have drastic consequences for summer water supplies. After a particularly dry winter in California’s Sierra Nevada, Yosemite Falls dwindled to a trickle during the summer of 2007. Photograph credit: Andy Sternberg (http://www.flickr.com/photos/revolute/814550903/
In parts of the United States, much of the water people rely on year-round ultimately comes from snow. In the west, mountain snowpack melts to fill reservoirs. Out on the plains, melting snow seeps into the ground to replenish soil moisture and help recharge aquifers. The 2012 winter received too little snowfall, contributing to a summer drought that desiccated crops and turned western forests into tinderboxes. A lack of snow has economic repercussions from the ski industry to manufacturing to farming: a layer of snow cover helps insulate crops like winter wheat. After last year’s devastating drought, many farmers are hoping for more snow.
Although this year’s lack of snow looks eerily like last year’s deficit in parts of the country, Dave Robinson of Rutgers University thinks there is room for hope. “We’re doing a little bit better than we were this time last year,” Robinson said. “This winter, the snow extent got off to a slow start, but by December the snow cover was pretty plentiful.” Snow extent retreated a bit in January, but February brought heavy snow to portions of the central and eastern part of the country. Robinson also pointed out snow doesn’t fall consistently throughout the season. Forecasters and climatologists know that there will be some ebb and flow to the snow cover extent.
In addition to tracking snow extent, Robinson also looks at snow depth. And this year, that is what worries him. “What is a little disconcerting is that where there is snow, it is not particularly deep, particularly in the western mountains,” he said. This is crucial for the spring snowmelt; a snowpack that develops over the course of a winter will have more water content than a limited number of quick hitting storms.
Let it snow
These maps show the 2011-2012 winter’s lower-than normal snow cover (top) compared to the 2010-2011 winter (bottom). Colors depict the percentage of days in which land was covered by snow: dark blues indicate only 10 to 20 percent of the time and the palest blue indicates nearly complete snow cover. The map was derived using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Photo credit: NASA Earth Observatory image by Jesse Allen, using data provided courtesy of Jeff Miller, NASA/GSFC.
Of course, snowfall is unpredictable, and too much snow in one place can be troublesome. “It’s a delicate balance, and you can have too much of a good thing.” Robinson said. Large snowstorms can disrupt ground and air travel, down power lines, and cause roofs to collapse. Up in the mountains, heavy snowpack can create dangerous avalanche conditions. Along river basins on the plains, too much snow can result in damaging floods during the spring melt season.
While we may not have to worry much about floods from snowmelt this year, Robinson stressed that it was too early to worry about a severe drought, either. “A couple of good March snow storms can turn things around,” he said. In some areas of the country, including much of the Rocky Mountains, March is often the snowiest month. He said, “We’ll know more two months from now. February and March are key.” February brought snow to parts of the country, particularly in the Eastern half, but March snowfall remains to be seen.
Winter weather has been unusual worldwide. While portions of the United States have been left high and dry, Paris and London received rare snowstorms, and parts of China have experienced record cold weather and snow. Scientists are still investigating how climate change might be fueling new and strange winter weather, but Robinson noted one clear result. “We’ve been losing snow cover earlier in the spring across the Northern Hemisphere. It’s not every year, but it is worrisome,” he said. “So that raises the question: In the future, will we need February to produce snow because it will be too late by March?” For now, however, much of the United States may still rely on a snowy spring to alleviate drought fears.
For more information about winter weather patterns and their relationship with sea ice, see this previous Icelights post: The Arctic Oscillation, winter storms, and sea ice