 Climate Monitoring / Climate of 1999 / Help
National Oceanic and Atmospheric Administration Climate of 1999 - April
Global Regional Analyses National Climatic Data Center, May 14, 1999
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Temperatures remained well above the long term average in April 1999, but they continued to show signs of cooling relative to the record warmth experienced in 1998. For details, see The Climate of 1998 - April's Climate in Perspective. Some of this cooling trend can be associated with mature La Nina conditions in the east equatorial Pacific, which was showing signs of weakening. The coldest anomalies were observed over Australia, while it was also below average over large portions of South America, western North America, and southern Africa. The largest warm anomalies occurred over eastern Europe, south Asia, northwest Africa, and eastern North America.
 Africa Temperature
| Temperatures over the northwest corner of the African continent were above average. These anomalies, in conjunction with below normal surface wetness, put stress on crops in the area. For details, see NOAA/USDA International Weather and Crop Summary. Temperatures in the center of the continent were near or slightly lower than the climatological mean, while South Africa was considerably warmer than average. This warm anomaly over South Africa has persisted since January 1999.
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Wetness Anomalies in Africa and the Middle East
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Iran and Iraq had the driest anomalies observed in this region. In fact, Iraq is currently affected by one of its worst droughts in the last 50 years. The government of Iraq has banned the planting of rice this season in order to conserve water. Dry anomalies were also observed over portions of the "Horn of Africa" and in parts of South Africa. These areas of dry anomalies have been quite persistant during March and April. Although northwestern Africa was wetter than normal over the past several months, a strengthening ridge of high pressure aloft led to dry conditions across portions of Morocco and northern Algeria in April. In contrast, surface wetness was above average across portions of the lower Great Rift Valley in southeastern Africa with flooding reported across portions of Malawi. Additional isolated positive anomalies were located over portions of southeastern Sudan and parts of Nigeria.
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European Temperature
| Temperatures across most of western Europe were near average, while central Europe experienced warmer than average conditions. Further east, the magnitude of the warm anomalies continued to increase. Unfortunately, the snow cover and lack of in situ observations limit our ability to analyze the temperature patterns over central Russia. Isolated negative anomalies were restricted to coastal Norway, the Baltic states, and parts of the Mediterranean basin.
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Wetness Anomalies in Europe
Positive wetness anomalies were associated with a trough extending across portions of the eastern European and Baltic coast regions into northwestern Russia. This area experienced more rain than snow during the month with a corresponding positive wetness anomaly. Areas in southeastern Europe were warmer than normal. These mild conditions led to an increase in spring snowmelt and flooding problems across portions of Belarus.
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Warm and dry conditions extended from the Ukraine into south central Russia. These conditions were associated with negative wetness anomalies. Scattered positive anomalies were also noted across portions of Russia.
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Asia Temperature
| Data over eastern Siberia was very sparse, but limited in situ data indicated that temperatures were cooler than average. This below normal pattern was also evident over northeastern China. Central China was slightly warmer than average, while further south in China temperatures were close to the climatology. Over the Indochina Peninsula temperatures were well below average. Over the remainder of southern Asia temperatures averaged above normal. In fact, over eastern India heat stress was responsible for several hundred deaths.
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Wetness Anomalies in Asia
| High positive wetness anomalies covered much of Manchuria in northeastern China. In contrast, negative anomalies were greatest across southeastern China in association with an upper air ridge that kept the area mainly warm. Dryness also extended westward across portions of Bangladesh and eastern India. Another large negative anomaly was observed in central Pakistan.
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Snow Cover in Europe / Asia
The most pronounced feature on this map is the area of negative snow cover anomalies over parts of Sweden, Finland, and portions of northwestern Russia. This area experienced fewer than usual days with snow cover because most of the region was unusually warm and wet with most of the precipitation falling as rain. Positive anomalies existed across portions of Norway and northern Russia, where temperatures were below normal.
Australia Temperature
| A weak trough over most of Australia kept the continent cooler than average. The largest negative anomalies occurred along the east and west coasts, with average conditions in the center of the country. In contrast, the sea surface temperature along the east and west coasts were near or warmer than normal. This indicates that the land surface anomalies were not directly associated with the sea surface temperature anomalies and may possibly be a consequence of above average rainfall.
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Wetness Anomalies in Australia
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Positive wetness anomalies were observed across portions of northern coastal Australia and along the western slopes of the Great Dividing Range in eastern Australia. The driest areas were in interior portions of the southwest and along the south coast. Overall the continent experienced an increase in positive wetness anomalies due to an active monsoonal trough and rainfall associated with Cyclone Gwenda that hit portions of northwestern Australia.
Sandy soils over portions of western Australia and tropical vegetation over the north coasts weakens the wetness signal observed by the satellite. Because of this, even though a large portion of western and northern Australia received record rainfalls, it is not apparent in this analysis. A detailed analysis for Australia can be found at Australian Bureau of Meteorology Precipitation Analyses - April 1999.
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North American Temperature
| A persistent trough over the western half of North America brought cold anomalies to the region during most of April. These temperatures coincided with above average snow cover. The adjoining Pacific Ocean also had temperature significantly colder than average. East of the Rocky Mountains, temperatures were above average from northern Canada to southern Mexico. The greatest of the these warm anomalies rimmed the Gulf of Mexico, where the surface water temperatures were also above average.
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Wetness Anomalies Across North America
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Storminess persisted for much of the month across the central plains into the mid Mississippi River valley. A weak but persistent trough over the desert southwest brought several precipitation events which lead to scattered wet anomalies across the Rockies. High positive surface wetness values are notable across portions of Iowa and North Dakota, while large negative surface wetness values were observed in southern Canada near Lake Winnipeg.
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Once again, the southeast was drier than usual which is not accurately depicted in this image, since dense vegetation obscures the surface water from the satellite.
Snow Cover Anomalies Across North America
Across the West, the major storm track shifted southward into northern California leaving the Pacific Northwest drier than normal. However, colder than normal temperatures allowed the large snow pack over the Pacific Northwest to remain largely intact during the month of April. The number of days with snow cover was well above average across much of western North America. One snowstorm in central Wyoming dumped almost 6 feet of snow in a three day period.
For a look at the month's daily snow cover across North America see Animated North American Snow Cover, April 1-30, 1999. The product is derived from NOAA/NESDIS's Satellite Services Division.
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In contrast, negative anomalies extended from portions of the upper Great Lakes northward to the western shores of Hudson Bay. This area was dry and milder than normal during the month due to a persistent ridge of high pressure.
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South America Temperature
| The majority of the South American continent had cooler than average temperatures. The largest of these anomalies occurred near Argentina's northern border. Temperatures were near average over the majority of eastern and southern Brazil and southern Argentina.
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South America Wetness Anomalies
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Large positive anomalies were observed over portions of Venezuela and Columbia, with both of these countries experiencing flooding rains that washed out bridges, destroyed homes and caused loss of life. A strong dipole structure was observed (in Bolivia and especially Argentina), which showed contrasting areas of below average wetness to the east and above average wetness to the west. There were other isolated dry areas in central and eastern Brazil where some brush fires were observed by satellite during the month.
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References:
Basist, A., N.C. Grody, T.C. Peterson and C.N. Williams, 1998: Using the Special Sensor Microwave/Imager to Monitor Land Surface Temperatures, Wetness, and Snow Cover. Journal of Applied Meteorology, 37, 888-911.
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 more information, refer also to ...
SSMI Derived Products
Global Historical Climatology Network (GHCN)
The Blended GHCN - SSM/I Product
The Global Temperature Anomalies
For further information on the historical climate perspective presented in this report, contact:
Alan Basist
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: alan.basist@noaa.gov
-or-
Tom Ross
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: tom.ross@noaa.gov
-or-
Mike Changery
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: mchangry@ncdc.noaa.gov
NCDC / Climate Monitoring / Climate of 1999 / Help
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