NH Snow Cover Extent
Data were provided by the Global Snow Laboratory, Rutgers University. Period of record is 1967-2011 (45 years).
The Northern Hemisphere snow cover extent during May 2011 was much-below average, marking the 3rd smallest (43rd largest) on record for the hemisphere. The May snow cover extent for the Northern Hemisphere was 2.79 million square km (1.08 million square miles) below the long-term average of 19.47 million square km (7.52 million square miles). This marks the seventh consecutive May with below-average snow cover extent for the hemisphere. During the month, both the Eurasian and North American land areas experienced below-average snow cover. According to a satellite analysis by the the Rutgers Global Snow Lab, during May, below-average snow cover extent was observed across central and northwestern Canada, most of Alaska, central and western Russia, and central Asia. Above-average snow cover was observed across the Rocky Mountains of the U.S., eastern Canada, eastern Russia, and central China. For the spring period (March-May), the Northern Hemisphere snow cover extent was also below average — the eighth consecutive spring with below-average snow cover extent for the hemisphere. The seasonal snow cover extent was 648,000 square km (250,194 square miles) below the long-term average, and ranked as the 19th smallest (27th largest) on record.
Did You Know?
Southern Hemisphere Snow Cover Extent
As part of its monthly State of the Climate Global Snow & Ice report, the National Centers for Environmental Information monitors monthly and seasonal snow cover extent across the Northern Hemisphere's major land areas — North America and Eurasia — using data from the Rutgers Global Snow Lab. Snow cover extent is sensitive to both regional temperatures and precipitation patterns across the mid and high latitudes, providing an important metric to measure the earth's climate system. By utilizing NOAA satellites, snow cover can be observed over all land areas, not just locations with surface-based observations, which can be sparse in non-developed areas of the globe.
Snow cover extent in the Southern Hemisphere is not currently examined for several reasons:
- Snow cover can only be measured over land areas, and not the ocean surface. Most of the surface area of the Southern Hemisphere is covered by ocean.
- The Southern Hemisphere land area located in the mid and high latitudes is very small, excluding Antarctica, when compared to the land area of the Northern Hemisphere at the same latitudes.
- The Antarctic continent is generally snow covered year round, with very little annual variation.
- Snow cover is difficult to measure across Antarctica and the high elevations of South America. These land areas are mostly covered by glaciers, and it is nearly impossible to distinguish snow cover from glacial ice using current satellite technology.
During May 2011, the North American snow cover extent was slightly below average, ranking as the 20th smallest (26th largest ). This is the seventh consecutive May with below-average snow cover extent for the continent. The monthly average snow cover extent was 309,000 square km (119,300 square miles) below the long-term average of 9.43 million square km (3.64 million square miles). According to data from the Rutgers Global Snow Lab, Canada and Alaska had below-average snow cover during the month, while the contiguous U.S. had slightly above-average snow cover. A snowy winter and spring across the western U.S., combined with below-average temperatures during May caused the mountainous regions of the U.S. to retain much of their snow cover this late into the season. During the spring period (March-May), North America had above-average snow cover extent. The seasonal snow cover extent was 449,000 square km (173,300 square miles) above the long-term average and ranked as the 12th largest (34th smallest) on record.
Eurasian snow cover extent during May 2011 was also below average, ranking as its 2nd smallest (44th largest) on record. The smallest May snow cover extent for Eurasia occurred in 2010. This is the seventh consecutive May with below-average snow cover extent for Eurasia. The May 2011 Eurasian snow cover extent was 2.48 million square km (957,500 square miles) below the long-term average of 10.03 million square km (3.87 million square miles). The spring (March-May) period snow cover extent for Eurasia was also below average. The seasonal snow cover extent anomaly of 1.10 million square km (425,000 square miles) below average ranks as the 10th smallest (36th largest) on record
Sea Ice Extent
According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent — which is measured from passive microwave instruments onboard NOAA satellites — averaged for May 2011, was 12.79 million square km (4.94 million square miles), 5.96 percent below the 1979-2000 average. This marks the third smallest May Arctic sea ice extent since records began in 1979. The two smallest May Arctic sea ice extents occurred in 2006 and 2004. May 2011 marks the 10th consecutive May and the 120th consecutive month with below-average Arctic sea ice extent. During May, below-average ice extent was observed on the Atlantic side of the Arctic, across the Barents and Labrador Sea, as well as the Bering Sea on the Pacific side. May Arctic sea ice extent was decreased at an average rate of 2.4 percent per decade.
The May 2011 Southern Hemisphere sea ice extent was 1.17 percent above the 1979-2000 average. This is the 14th smallest (20th largest) May Southern Hemisphere sea ice extent on record. May Antarctic sea ice extent has increased at an average rate of 2.2 percent per decade, although there is considerable interannual variability. During May, Antarctic sea ice continued its annual growth cycle, after reaching its annual minimum extent at the end of February.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.