Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

HOME > Expert Assessments > Climate Diagnostics Bulletin


Extratropical Highlights - February 2001

1. Northern Hemisphere
The circulation during February featured a persistent pattern of above-normal heights across the central North Pacific, the Gulf of Alaska, the southeastern United States, and the high latitudes of the North Atlantic, and below-normal heights over eastern Siberia and the western United States (Figs. E10, E12). One aspect of this large-scale pattern was a strong negative phase (-1.1) of the North Atlantic Oscillation (Table E1, Figs. E7, E8). A second aspect of the pattern was a well-defined jet exit region over the central North Pacific of the East Asian jet, and a confinement of the jet core to well west of the date line (Fig. T22). These features of the East Asian jet and jet exit region are typical of mature cold episode conditions during the NH winter and early spring season, and are linked to the La Niņa-related enhancement of the subtropical ridge over the western North Pacific and the subtropical trough over the central North Pacific (Fig. T22).On a regional basis this overall anomaly pattern contributed to exceptionally warm temperatures over Alaska and the southeastern United States during February, and to below-average temperatures over the northern plains and south-central Canada (Fig. E1). Above-average temperatures were also observed across central and much of southern Europe during the month.

The prominent precipitation anomalies during February reflected a continuation of exceptionally dry conditions across both the southeastern United States and the Pacific Northwest (Fig. E3). Below-average precipitation was also observed over portions of southern Europe (Fig. E4), while extreme northern Europe, southeastern Scandinavia, and western Russia recorded above-average precipitation.

a. North America

The circulation over North America featured a persistent pattern of above average heights over the southeastern U.S. and below-average heights over the western U.S. (Fig. E10). These conditions were associated with a pronounced split flow pattern that covered western North America. The northern branch of this split flow extended northward to Alaska and then southeastward to the Great Lakes region, and the southern branch extended from Southern California to the mid-Atlantic States. Farther downstream the confluence of these two flow streams over the central and eastern United States contributed to an axis of heavy precipitation extending from northeastern Texas to the eastern Great Lakes.

Above-average precipitation during February also extended from the Great Lakes to northeastern Canada. This area was situated in a region of increased cyclonic curvature within the base of the Hudson Bay low.

Precipitation was again significantly below average across Florida and the southeastern U.S. during February (Fig. E3). A persistent pattern of above-average heights and anomalously low rainfall has prevailed across these areas for much of the past three years in association with ongoing La Niņa conditions. During the last year (March 2000 – February 2001), Florida recorded its second lowest rainfall total in the historical record dating back to 1895. The southeastern U.S. also recorded anomalously warm conditions (1°-2° C above average) during February (Fig. E1).

b. Europe

Above-average heights covered the high latitudes of the North Atlantic during the second half of February, which contributed to an overall negative phase of the North Atlantic Oscillation (NAO) (Table E1, Figs. E7, E8). This circulation was accompanied by anomalously warm and dry conditions across southern Europe (Figs. E1 and E3), and above-average temperatures over central Europe.

c. Stratosphere

Strong winter stratospheric warming over the Northern Hemisphere polar region reached peak levels at the end of January and early February (Fig. S4). The unusually long duration of strong vertical transport of wave energy during January and February (Fig. S7) contributed to the strength of the stratospheric warming. By mid-February, strong positive height anomalies (Fig. S1) prevailed over the north polar region in the upper troposphere and stratosphere, as the polar anticyclonic circulation strengthened throughout the stratosphere. Associated with these temperature (Fig. S3) and circulation anomalies, there were also strong positive total ozone anomalies which prevailed over the north polar region (Fig. S6). Similar features accompanied a strong north polar winter warming in February 1999, which was the first major warming to occur since 1991.

2. Southern Hemisphere

The circulation during February was dominated by a persistent pattern of above-average heights extending from southeastern Australia to central South America, and by below-average heights across the high latitudes of the South Pacific and southern South America (Figs. E16, E18). This anomalous circulation was associated with above-average temperatures over central Argentina and below-average temperatures over southern South America (Fig. E1). It was also associated with significantly warmer-than-average conditions across southeastern Australia, with temperatures in many areas exceeding the 90th percentile (Fig. E3).

The rainy season in southern Africa typically extends from October to April, with the peak in rainfall typically occurring during January-February. During February 2001 significantly above-average rainfall was recorded in southeastern South Africa and Mozambique (Fig. E3). These rains were preceded by below-average rainfall during January 2001 (Fig. E4).

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
5830 University Research Court
College Park, Maryland 20740
Page Author: Climate Prediction Center Internet Team
Page last modified: August 24, 2007
Information Quality
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities