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.
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
|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
Regional Analyses pages for more details on regional climate in
the United States and throughout the world.
|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.
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.
|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
|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.