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Global Highlights:
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| The April land and ocean combined temperature averaged across the globe was 0.55°C (0.99°F) above the 1880-2000 long-term mean. This was the second warmest April in the 1880-present record, and was second only to April 1998 when the combined land and ocean temperature anomaly was 0.74°C (1.33°F). Ocean surface temperatures also ranked as second warmest on record (0.39°C [0.70°F] above average), which was 0.13°C (0.23°F) cooler than during the El Niño episode of 1998. Temperatures averaged over land surfaces were 0.92°C (1.66°F) above average, or the third warmest April on record, but 0.31°C (0.56°F) cooler than the record April land temperature set during the El Niño event of 1998. |  larger image |
| A gradual dissipation of La Niña conditions continued during April as temperature anomalies returned to more neutral values. Tropical temperature anomalies in the oceans were 0.34°C (0.61°F) above the long term mean. Temperature anomalies in the extratropical regions were even higher, most notably in the southern hemisphere, where the combined land and ocean temperature was 0.62°C (1.12°F) above average. This was the second warmest April on record south of 20°S latitude. |  larger image |
| Across land areas, anomalies were slightly positive in the tropics, with temperatures 0.64°C (1.15°F) above average. Extratropical land areas of the Northern Hemisphere experienced their 4th warmest April, or 1.19°C (2.14°F) above average. |  larger image |
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A reversal from the March 2001 mean circulation pattern over North America brought an upper level trough of low pressure and subsequent cooler than average temperatures across the western United States. Downstream ridging brought much above average warmth over the central and eastern U.S. into Canada. Other positive temperature anomalies of 2 to 5°C (3.6 to 9.0°F) were common across eastern Europe, western parts of the former Soviet Union and the Middle East. Cooler weather with negative departures from 2 to 3°C (3.6 to 5.4°F) occurred in central and southern Australia |
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| April was a very wet month across parts of western Alaska and the upper Midwest of the United States where precipitation totals locally exceeded 100 mm (3.94 inches) above average. Heavier than average precipitation also continued this month across much of western and central Europe. Precipitation deficits were common across the eastern and southern U.S., most of Australia, eastern Brazil as well as eastern China to Japan. A lack of significant rainfall again this month across parts of the Middle East continued to exacerbate severe drought conditions in Pakistan and Afghanistan. | 
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Temperatures measured in the lowest 8 km (5 miles) of the troposphere were 0.17°C (0.31°F) above the long term average (1979-1998). This was the 4th warmest April, but far below the record anomaly of 0.75°C (1.35°F) set during the strong El Niño of 1998. |
Over the Northern Hemisphere, temperatures in April above the surface were also 4th warmest, with a positive departure of 0.28°C (0.50°F). Southern Hemisphere temperatures were near to the long term average, with temperatures averaging just 0.06°C (0.11°F) above the mean. In the lower stratosphere, the global temperature was 0.37°C (0.67°F) cooler than the average, which ranked as the 5th coolest April during the satellite period of record which began in 1979. This was the 8th consecutive April with below average stratospheric temperatures. Both the Northern and Southern Hemispheric temperatures were below the average, with departures of -0.45°C (-0.81°F) and -0.29°C (-0.52°F), respectively. Lower tropospheric and lower stratospheric temperature data are collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by NASA and the Global Hydrology and Climate Center at the University of Alabama in Huntsville.
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| The Hovmüller diagram depicts sea surface temperatures in the equatorial eastern Pacific since the beginning of 1997. Large positive temperature anomalies (El Niño) developed late in 1997 and continued into 1998. Thereafter, La Niña conditions (cooler sea surface temperatures) have persisted. During the last few months, negative anomalies have decreased, suggesting a continued weakening of La Niña and a return toward more neutral conditions. | 
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For additional details on precipitation and temperatures in April see the Global Regional page .
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References: Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global
Historical Climatology Network Database. Bull. Amer. Meteorol.
Soc., 78, 2837-2849. Questions?For questions on technical or scientific content of this report, please contact: Ahira Sánchez-Lugo:Ahira.Sanchez-Lugo@noaa.gov For general climate monitoring questions, please contact: CMB.Contact@noaa.govFor climate data orders, please contact the National Climatic Data Center's Climate Services and Monitoring Division: NCDC.Orders@noaa.gov
  
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