IRI Climate Digest
April 2000
April Global Climate Summary
Climatological Background In April, the sun's
migration into the Northern Hemisphere has begun, bringing springtime to
the northern mid-latitudes. The monsoon systems which still linger south
of the equator will move northward following the solar heating of the continents
in the next two months. In the southern hemisphere fall has arrived, with
cooler temperatures and a strengthening of the mid latitude storm tracks.
Monthly Mean Temperature (1961-1990), data from the Climate Research
Unit, University of East Anglia
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Monthly Mean Precipitation (1961-1990), with data from
the Climate Research Unit, University of East Anglia
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Temperatures Over Land
North America: In contrast to recent months, only the
western United States experienced above average temperatures. Near
average conditions prevailed elsewhere except for below average temperatures
in the southeastern United States.
Europe and Asia: With the exception of southeastern Asia,
temperatures continued above average over most of the entire region.
Temperatures were more than 4C above average from eastern Europe eastward
to the Aral Sea.
Africa: Temperatures were above average across most of
northern and eastern Africa as well as Madagascar. Near average conditions
were observed elsewhere.
Australia: Western Australia once again experienced below average
temperatures. The remainder of the continent saw near average conditions.
South America: Temperatures were 1 to 2C above average across
central and southern Brazil as well as Uruguay, Paraguay, Bolivia and northern
Argentina.
Temperature Difference from the 1961-1990 mean, with
data from NCEP Climate Prediction Center, CAMS.
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Precipitation
Africa: Unusually dry weather continued over eastern Africa
from southern Ethiopia southward into Kenya, southern Somalia and northern
Tanzania.
Above average rainfall was again observed in southern Africa in a band
extending from northern Angola eastward across Botswana, Zimbabwe and southern
Mozambique. Rainfall in central Morocco brought limited relief to
dry conditions there.
Australia: Tropical cyclone activity was primarily responsible
for above average precipitation in northeastern Western Australia and much
of the Northern Territory.
Indonesia: Above average rainfall was observed throughout
the region with localized very heavy rains.
Southeast Asia: Precipitation was well above average across
Malaysia as well as much of Thailand and Burma.
China: Below average rainfall was observed across
the North China Plain. Locally heavy rains along the central east
coast resulted in above average precipitation there.
South America: Below average rainfall occurred over western
Venezuela and central Columbia as well as portions of southeastern Brazil.
Above average rainfall totals were observed in northwestern Argentina and
from eastern Venezuela eastward to French Guiana.
Middle East: Rainfall continued to be below average across much
of the Middle East eastward to Afghanistan and Pakistan.
United States: Below average rainfall continued in the upper
midwest.
Europe: Above average rainfall was observed over northern
and western Europe including the Iberian peninsula which helped to ease
dry conditions there. Below average precipitation was reported across
central Europe from Poland southward to the Mediterranean Sea.
Precipitation Difference from 1961-1990 mean, with
data from NCEP Climate Prediction Center, CAMS-OPI.
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Oceanic Conditions
Tropics: The moderate La Niña (colder than average)
conditions in the central equatorial Pacific weakened from the previous
month and are expected to continue to weaken. The positive anomalies in
the eastern equatorial Pacific continued to strengthen but remain a near
surface phenomenon in the ocean. This evolution is unlike a typical El
Niño onset but the warm ocean temperatures may enhance rainfall
locally.
Extratropics: Above average SST anomalies continued to
dominate the mid latitude oceans of both Northern and Southern hemispheres,
as has been the case for most of the past two years. Colder than average
SSTs have been expanding in the North Pacific.
Monthly Sea Surface Temperature Difference from the 1950-1979 mean,
with data from the Environmental Modeling Center, NCEP/NOAA.
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