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 Niña 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.

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 90^th percentile (Fig. E3).