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 April 2011 was below average, marking the 15th smallest (31st largest) on record for the hemisphere. The April snow cover extent for the Northern Hemisphere was 919,000 square km (354,825 square miles) below the long-term average of 30.5 million square km (11.8 million square miles). This is the eighth consecutive April with below average snow cover extent for the Northern Hemisphere. The Eurasian land area experienced much below-average snow cover extent during the month, while North America had above-average snow cover. According to a satellite analysis by the Rutgers Global Snow Lab, above-average snow cover was observed across the northern U.S. and southern Canada, western Russia, and the Tibetan Plateau. Below-average snow cover was observed across interior regions of the western U.S., central and eastern Russia, the European Alps, and most of central Asia.
During April 2011, the North American snow cover extent was above average, ranking as the 10th largest (36th smallest) on record. The monthly average snow cover extent was 846,000 square km (326,642 square miles) above the long-term average of 13.2 million square km (5.1 million square miles). According to data from the Rutgers Global Snow Lab, Canada, the contiguous U.S., and Alaska all had above-average snow cover during April. An active storm pattern across the central U.S. during the month brought above-average snowfall to portions of the northern U.S. and southern Canada.
Eurasian snow cover extent during April 2011 was much below average, ranking at the fifth smallest (41st largest) on record. This is the fifth consecutive April with below average snow cover for Eurasia. Above normal temperatures across Russia during April caused much of the snow pack to melt, limiting the monthly snow cover extent. The April Eurasian snow cover extent was 1.76 million square km (0.66 million square miles) below the long term average of 17.3 million square km (6.7 million square miles).
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 April 2011, was 14.15 million square km (5.46 million square miles) — this value is 5.68 percent below average. This is the fifth smallest (29th largest) April Arctic sea ice extent since records began in 1979. April 2011 marks the 12th consecutive April and the 119th consecutive month with below-average Arctic sea ice extent. During April, ice extent was below average across much of the Atlantic side of the Arctic, including the Barents Sea and along the Canadian Maritimes. On the Pacific side, the Bering Sea had more ice coverage than what is average for this time of year. April Arctic sea ice has decreased at an average rate of 2.6 percent per decade.
The April 2011 Southern Hemisphere sea ice extent was 7.68 percent below the 1979-2000 average. This is the fourth smallest April Southern Hemisphere sea ice extent on record, behind April 2006, 1981, and 1980. April Antarctic sea ice extent has increased at an average rate of 2.2 percent per decade, although there is considerable interannual variability. During April, 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.