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National Oceanic and Atmospheric Administration Climate of 1999 - April Global Analysis National Climatic Data Center, 14 May, 1999

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Climate of 1999: April Overview Detailed Climate Perspectives . . . Global Analysis Global Regional Analyses U.S. National Analysis U.S. Regional/Statewide Analyses Extreme Events 1999 Monthly Reports

Temperature

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Mean monthly temperature anomalies for April (using a base period 1880-1998) are shown in the figure to the left. Global temperatures were considerably cooler in April 1999 than in the record warm April 1998 but continued to be higher than the long term mean. The average temperature over land and ocean was 0.44 C above the 1880-1998 mean, 0.32 C less than the record anomaly recorded in 1998. Although the drop in temperature was due to cooler conditions over both land and ocean, the most significant cooling occurred over the oceans. The average sea surface temperature anomaly dropped almost in half from 0.54 C in April 1998 to 0.28 C in 1999. April land surface temperatures averaged 0.84 C above the long term mean in 1999, down from 1.28 C in 1998.

The drop in both land and ocean temperatures is a continuation of the trend toward cooler temperatures that began last year with the transition from El Niño to La Niña conditions. This figure shows the difference in land surface temperatures between the mature El Niño conditions in April 1998 and La Niña in April 1999. (These are NOT temperature anomalies. They are simply April 1999 temperatures minus April 1998 temperatures. Blue dots indicate cooler temperatures in 1999.) Some areas were warmer in 1999, but blue dots extend across a large area of the world, indicating that temperatures were cooler throughout most areas.

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Although temperatures are generally lower in 1999 when compared with 1998's extremely warm temperatures, this figure of global anomalies shows that temperatures were still well above average in large parts of the world. The largest positive anomalies occurred throughout Canada and areas of western Russia. Above average temperatures were also widespread throughout Europe and Asia. Large positive anomalies have been recorded in Canada for the past several months while below average temperatures have been measured in northern sections of Russia.

Although Russian data is limited, cooler than average temperatures are shown in northeast and northwest areas of Russia again in April. The western third of the United States and southern areas of South America also experienced below average temperatures in April. See the U.S. Regional / Statewide Analyses pages and the Global Regional Analyses pages for more details on regional climate in the United States and throughout the world.

Precipitation

As shown in the adjacent figure, preliminary global precipitation (land only) averaged 5.0 mm (0.20 inches) above the long term mean (1900-1998) in April. This continues a pattern of above average precipitation in 1999 with above average values every month this year.

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However, in April the areal coverage of anomalies greater than 100 mm was less than in previous months. The areal coverage of negative anomalies less than -100 mm was also lower in April, indicating that precipitation in many areas was closer to average this month. Precipitation departures less than 25 mm are shown in the figure below for many regions of the world, particularly much of Asia, Africa and a large part of Europe. Anomalies greater than 100 mm were scattered throughout several areas of the world, e.g. portions of southeastern China, the South Pacific islands and parts of South America and the central United States.

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Much of Europe was slightly wetter than average in April, while near normal precipitation fell across the Asian continent. Some areas in southern and eastern China that had been experiencing drought conditions the past several months were wetter than average in April. As they have in recent months, most islands in the South Pacific continued to receive above average rainfall in April. Above average precipitation also fell across the central plains and Midwest areas of the United States. Venezuela, much of Argentina and isolated areas of Brazil also received precipitation amounts above their long term averages.

Global Surface Wetness

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Surface wetness was above average in large areas of the central United States, Manchuria, northern Argentina, and Indochina. There were small positive anomalies in central Russia, northern South America, central Africa and Baltic Sea area. The largest negative anomalies occurred in southern Russia, Ukraine, and southeastern China, while scattered negative values covered portions of central Russia, the horn of Africa, eastern Argentina, and eastern India.

Global Snow Cover

There were large areas of above average snow cover in western North America and north central Russia. Both of these areas had cooler than normal temperatures, which allowed the snow to remain on the ground longer than usual. There were also smaller areas of positive anomalies in southern Siberia. In contrast, negative anomalies covered large areas in central Canada as well as the region surrounding the Baltic Sea. Both of these areas had temperatures above average for April, which caused the snow cover to melt earlier than usual. There are also smaller areas with below average snow cover in central China.

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Animations of April daily snow cover are also available for the Northern Hemisphere, the United States, and Asia and Europe. These images were provided by the National Environmental Satellite, Data, and Information Service.

For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:

Climate Services Division
NOAA/National Climatic Data Center
151 Patton Avenue, Room 120
Asheville, NC 28801-5001
fax: 828-271-4876
phone: 828-271-4800
email: ncdc.orders@noaa.gov

For questions about this report, please contact:

David Easterling
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: david.easterling@noaa.gov

Mike Changery
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: mchangry@ncdc.noaa.gov

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