Global Analysis - April 2001
Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective September 2012, the GHCN-M version 3.2.0 dataset of monthly mean temperature replaced the GHCN-M version 3.1.0 monthly mean temperature dataset. Beginning with the August 2012 Global monthly State of the Climate Report, released on September 17, 2012, GHCN-M version 3.2.0 is used for NCDC climate monitoring activities, including calculation of global land surface temperature anomalies and trends. For more information about this newest version, please see the GHCN-M version 3.2.0 Technical Report.
*The GHCN-M version 3.1.0 Technical Report was revised on September 5, 2012 to accurately reflect the changes incorporated in that version. Previously that report incorrectly included discussion of changes to the Pairwise Homogeneity Algorithm (PHA). Changes to the PHA are included in version 3.2.0 and described in the version 3.2.0 Technical Report. Please see the Frequently Asked Questions to learn more about this update.
Global Highlights:
|
Contents of this Section: |
|
| 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 |
 larger image |
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 |
|
| 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. | 
larger image |
Equatorial Temperatures
| 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. | 
larger image |
For additional details on precipitation and temperatures in April see the Global Regional page .
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.
