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Mature La Nina conditions in the east equatorial Pacific continues to keep cooler than average temperatures over the tropical eastern Pacific over the Northern Hemisphere. In fact, the coldest SST anomalies are just west of North America. The warmest SST anomalies existed over the extra-tropical Western Pacific in the Northern Hemisphere, and they extended east of the International Date Line. This pattern is also linked to the mature La Nina conditions over the Pacific Basin. There was a distinct wave temperature pattern across the Northern and Southern Hemispheres. Warm anomalies existed over eastern Northern America, Western Europe, central Russia, and the Central Pacific, with cold anomalies covering the areas in between. In the Southern hemisphere, warm anomalies were noted over central Australia, eastern Pacific, Central Atlantic, and Western Indian Ocean, while cold anomalies dominated South America, southern Africa, as well as portions of the Indian and central Pacific Oceans.
General May 1999 mean upper air circulation patterns anomalies are available for the Northern Hemisphere and Southern Hemisphere.
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| The northern tier of the continent generally had temperatures above average, and this corresponded with warmer than average temperatures over the majority of the landmass surrounding the Mediterranean Sea. Persistent high pressure dominated this region during May, which promoted these hot conditions. Warm anomalies were noted over the Middle East and the southwest corner of the Asian continent. The atmospheric pattern also kept most of this region drier than average during the month. Further south, over the interior of Africa, temperatures were slightly cooler than average, while anomalies across most the equatorial Africa were rather weak. Positive temperature anomalies were also noted over interior sections of south Africa over Botswana. |  |
Wetness Anomalies in Africa and the Middle East
larger image Severe drought continues to impact the Middle East. Countries most severely impacted are: Jordan, Syria, Iran, Iraq and Afghanistan. The drought is the "worst in decades" according to U.N. agencies and has persisted in this region for most of the March - May period. Dry anomalies and drought conditions were also observed over portions of the "Horn of Africa" and across parts of the Sudan westward along the Sahel at about 10 degrees North latitude. A ridge of high pressure across northwest Africa kept that region of the continent dry and warm. In contrast, surface wetness was above average across portions of southern Sudan and in portions of the Great Rift Valley across parts of Tanzania, Zambia and Malawi. Positive anomalies were noted across interior South Africa while dry anomalies were observed along the coast.
European Temperature
An upper level ridge kept temperatures over much of western Europe well above average. These anomalies were strongest to the south and west, and transitioned into cooler than average conditions in Scandinavia. To the east of the ridge a trough in eastern Europe produced temperatures that were cooler than usual. The ridge over western Europe extended southeast to the Mideast, where unusually warm temperatures persisted during most of May. 
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Wetness Anomalies in Europe
The largest negative wetness anomalies were associated with a trough of low pressure extending across portions of northwestern Russia southward toward the northern shores of the Black and Caspian seas. The northern part of this region experienced cooler than average temperatures allowing much of the precipitation to fall as snow during the month which led to a negative surface wetness anomalies. Spotty negative wetness anomalies were observed across portions of the Crimea with more extensive negative wetness anomalies across Turkey.
larger image Largest positive wetness anomalies were observed over central Russia white scattered positive wetness anomalies were observed near the Yugoslav, Hungarian and Romanian border and across portions of south central Russia. Flooding was a problem across portions of south central Europe due to earlier springtime heavy rains and rapid spring snowmelt.
European Snow Cover
Positive snow cover anomalies extended across parts of northern Sweden, Finland, and into north central Russia. These anomalies were associated with a low pressure trough which kept the area cooler and wetter than average. Consequently the snow pack does not melt away as early as expected. 
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Asia Temperature
larger image A upper level ridge kept much of north central Asia warmer than average. In fact, some the warmest anomalies across the globe covered this area. A persistent trough existed both to the east and west of the ridge, and these areas were cooler than usual. Most of southern Asia was cooler than average, since the region was largely covered by clouds and above normal rainfall. This weather pattern helped alleviate the dry conditions that persisted over southeastern China during the previous months. In contrast, southwestern Asia was under an upper level ridge, which produced warm dry conditions.
Wetness Anomalies in Asia
Highest positive anomalies were reported across parts of Laos, Cambodia, and Thailand with some flooding reported in central and southern Thailand. Scattered pockets of high positive and negative wetness anomalies covered much of central and eastern China. Flooding was reported in the Hunan province in southeast China. Positive anomalies were also noted over southeast Pakistan and coastal areas of extreme western India where Typhoon 02A - the second of the season - brought flooding rains. More details on the storm are available in the NCDC May 1999 Climate Watch. Scattered negative anomalies were noted across portions of interior Pakistan, Afghanistan, Iran and southern sections of the former Soviet Union. 
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Asian Snow Cover
Strong negative anomalies were apparent over central Russia. This area was under the influence of a strong ridge of high pressure during most of the month which kept the region quite dry and mild with any precipitation falling mainly as rain. These negative anomalies extended southward across portions of Mongolia.
larger image Mild later spring temperatures along with the lack of snow cover across parts of Siberia led to numerous fires in the pine forests in the region. As of the end of May, fuel and equipment shortages, as well as the remoteness of the area, hampered efforts to contain the blaze. For a look at the month's daily snow cover across Asia/Europe see Animated Europe/Asia Snow Cover, May 1-30, 1999. The product is derived from NOAA/NESDIS's Satellite Services Division.
Australia Temperature
Persistent cloud cover, and wet surface conditions over northern Australia kept this portion of the continent cooler than average. A ridge over the center of the continent kept that area warmer than usual. The eastern and western margins of the continent received persistant rainfall and cloud cover, which kept temperatures near average throughout most the month. Further to the southeast the sea surface temperature were well above average. A good portion of central and southern New Zealand has above average temperatures. 
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Wetness Anomalies in Australia
larger image Australia experienced a more active weather pattern with several cold fronts bringing precipitation to portions of both coasts. In fact, a strong cold front at midmonth brought some early snowfall to the eastern ranges and foothills. In contrast heavy rains led to record rainfalls across portions of western Australia, with isolated spots registering their wettest May for the century. Positive wetness anomalies were also observed across portions of southeastern Australia as well. The driest areas were across the interior portion of the continent. Sandy soils over portions of western Australia and tropical vegetation over the north coast weaken the wetness signal observed by the satellite. Because of this, even though a large portion northern Australia had ample rainfall, it is not apparent in this analysis. A detailed analysis for Australia can be found at Australian Bureau of Meteorology Precipitation Analyses - May 1999.
North American Temperature
A persistent trough over the west half of North America brought unusually cool temperatures to the region during most of May. These temperatures contributed to the above average snow pack at the higher elevations of the Rocky Mountains. The trough extended over the adjoining Pacific ocean, where temperatures were also cooler than average. In contrast, an upper level ridge over the eastern portion of the continent centered near the U.S. - Canadian border kept that area much warmer than usual. Further southward, over the southeastern U.S., temperatures were generally near average. 
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Wetness Anomalies Across North America
larger image Frequent storminess across parts of the Central Plains states led to a moisture surplus across areas from Nebraska northward to central Canada. Positive wetness anomalies were also observed across a large portion of Canada east of Hudson Bay. The positive wetness anomalies across parts of eastern Canada were due to melting snowcover and most precipitation falling as rain. Portions of the eastern U.S. were drier than normal, with the southeastern U.S. from parts of Virginia to northern Florida experiencing drought conditions. These conditions are not accurately depicted in this image, since dense vegetation obscures the surface water from the satellite.
Snow Cover Anomalies Across North America
A persistent ridge of high pressure surrounding the Hudson Bay region most of the month led to below average precipitation and negative snow cover anomalies. A trough of low pressure across the western U.S. states let to positive snow cover anomalies across the higher elevations of the Rockies and the Pacific Northwest. In fact, as of noon on 5/13/99, Mount Baker, Washington set a new "unoffical" world snowfall record with 1124 inches of snow recorded this season.For a look at the month's daily snow cover across North America see Animated North American Snow Cover, May 1-30, 1999. The product is derived from NOAA/NESDIS's Satellite Services Division.
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South America Temperature
The majority of the South American continent had cooler than average temperatures. This signature corresponds to La Nina conditions in the Pacific Ocean. The largest of these anomalies occurred in Paraguay. Temperatures were near average over the northern tier of the continent. 
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South America Wetness Anomalies
larger image Large negative anomalies were observed over portions of southern and northern Argentina with central and interior sections having positive anomalies. Additional negative anomalies were observed near the Bolivia-Paraguay-Argentina border. Across northern South America large positive anomalies were noted in portions of Columbia and Venezuela. Tropical vegetation over portions of the continent weakens the wetness signal observed by the satellite. Because of this, even though a large portion of the Amazon river basin had ample rainfall, this is not apparent in the analysis.
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-or-
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: alan.basist@noaa.gov
Tom Ross-or-
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: tom.ross@noaa.gov
Mike Changery
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: mchangry@ncdc.noaa.gov
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