Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective September 2012, the GHCN-M version 3.2.0 dataset of monthly mean temperature replaced the GHCN-M version 3.1.0 monthly mean temperature dataset. Beginning with the August 2012 Global monthly State of the Climate Report, released on September 17, 2012, GHCN-M version 3.2.0 is used for NCDC climate monitoring activities, including calculation of global land surface temperature anomalies and trends. For more information about this newest version, please see the GHCN-M version 3.2.0 Technical Report.
*The GHCN-M version 3.1.0 Technical Report was revised on September 5, 2012 to accurately reflect the changes incorporated in that version. Previously that report incorrectly included discussion of changes to the Pairwise Homogeneity Algorithm (PHA). Changes to the PHA are included in version 3.2.0 and described in the version 3.2.0 Technical Report. Please see the Frequently Asked Questions to learn more about this update.
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.
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.)
US National Overview
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
|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
|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.
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