Winter (DJF) 1999 Global Climate Report

The December 1998 - February 1999 season was dominated by the mature La Niña (cold water) conditions in the east equatorial Pacific. This corresponded to colder than normal temperatures in southern Europe, northwestern Africa and western Australia. The eastern two thirds of North America was warmer than normal, as a result of fewer than normal Arctic outbreaks. A persistent ridge over northeastern Africa and the Middle East kept that region warmer and drier than normal. It was also warmer and drier over China throughout the season. A broad ridge over Asia resulted in above normal temperatures over most of Russia except for the eastern-most portion. A persistent trough off the northwest coast of North America produce near record rain and snow cover in the area. Drought was widespread in southern Africa during the season.

Global mean land temperature anomalies for the period December-February (using a base period 1880-1998) are shown in the above figure. The anomaly for the 1998-1999 season was well above the mean value. In fact, this 1998-1999 season was the third warmest since 1880. The curved yellow line is a nine-point binomial filtered value which shows the decadal-scale variations.

Globally averaged precipitation for the three-month period December 1998 through February 1999 was 31.12 millimeters above the 1900 - 1998 mean. Although precipitation averaged well above normal for the globe as a whole, there were many areas that were drier than normal during the period. (See the Global Analysis page for more information.)

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The predominant upper-level flow pattern for the Winter Season was a Pacific onshore flow which provided copious amounts of rainfall for the Pacific Northwest and record snowfalls for the higher elevations. Once these storm systems crossed the Rockies, they were much weaker and provided only limited amounts of moisture. This near-persistent zonal flow permitted only a few intrusions of arctic air, most notably during late December and early January. The lack of arctic air masses allowed for the second warmest winter since 1895 for the contiguous United States.

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Preliminary data for December 1998 through February 1999 across the contiguous United States indicate that temperatures averaged well above the long-term mean, ranking as the second warmest December-February since 1895. The warmest winter season was 1991-1992. The three warmest winter seasons have occurred in the last 8 years. The bars in this graph are departures from the 1895-1998 mean. The curved line is a nine-point binomial filtered value which shows the decadal-scale variations.

Precipitation for the contiguous United States, as a whole, was near normal for the period December 1998 through February 1999, based on preliminary data. The bars in this graph are departures from the 1895-1998 mean. The curved line is a nine-point binomial filter which shows the decadal-scale variations.

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Numerous weather related natural disasters occurred during the December 1998-February 1999 period. Major highlights included outbreaks of tornadoes in the U.S. in January 1999 with a record number of tornadoes (169), which is about ten times the January climatological norm, and heavy precipitation (over 60 inches in some locations) across portions of the U.S. Pacific northwest. Heavy snowfall lead to numerous and fatal avalanches across portions of Europe during this period as well..