Extratropical Highlights –February 2023

 

1. Northern Hemisphere

The 500-hPa circulation during February resembled a positive Arctic Oscillation pattern with below-average heights over northern latitudes and above-average heights over the middle latitudes (Fig. E9).  During the month of February, the North Atlantic Oscillation was also positive (Fig. E7) and in combination, these two teleconnections contributed to the above-average temperatures and below-average precipitation across much of Eurasia (Figs. E1, E3). In North America, colder than average conditions were observed for much of Canada and the western U.S. while both Alaska and the eastern U.S. recorded warmer than average conditions. The main precipitation signals for North America were primarily in the U.S. and included above-average rainfall in the Great Lakes region and below-average rainfall for the Southeast, much of West Coast, and Alaska Panhandle (Fig. E3).

 

a. North America

The February height pattern over North America was distinguished by anomalous ridging over the North Pacific Ocean and the eastern half of the U.S., while Canada and much of Alaska observed moderate anomalous troughing, and the western U.S. observed mild anomalous troughing (Fig. E9). The anomalous ridge over the eastern U.S. contributed to warmer than average and drier than average conditions, to include some areas reaching the 90th percentile of above-average temperature conditions (Fig. E1). Conversely, the anomalous trough in the western U.S. contributed to colder than average conditions, to include some areas reaching the 30th percentile of occurrences (Fig. E1). Precipitation patterns across the U.S. included above-average rainfall in the Great Lakes region, where some areas reached the 80th percentile of occurrences, and moderately below-average (30th percentile) rainfall conditions were observed along the U.S. Pacific Northwest, Southeast and Alaska Panhandle (Figs. E3, E5, E6).

 

b. Eurasia

The 500-hPa height pattern across much of Eurasia featured anomalous ridging (Fig. E9).  This pattern likely contributed to the widespread above-average temperatures, which reached the 70th percentile of occurrences for much of the region (Fig. E1). The main precipitation signals included drier than average conditions for western Europe and slightly wetter than average conditions for eastern Europe (Fig. E3). 

 

2. Southern Hemisphere

The 500-hPa pattern in the Southern Hemisphere resembled an anomalous wave-train pattern across the South Pacific Ocean (Fig. E15).  Warmer than average and drier than average conditions were observed across much of South America while the north-central territories of Australia observed cooler than average conditions and drier than average conditions were observed across the southern half of the country (Figs. E1, E3, E4).

The South African monsoon season runs from October to April. During February, rainfall was well above-average, reaching the 90th percentile of occurrences (Fig. E4). As a comparison, in the previous months of December and January, observed rainfall in the monsoon region of South Africa was relatively near-normal (~50th percentile, Fig. E4).