Extratropical Highlights -- May 2025

 

1. Northern Hemisphere

The 500-hPa circulation during May resembled a wavetrain pattern across North America and Europe (Fig. E9). The main land-surface temperature signals were above average temperatures across western North America, Europe, and central Asia (Fig. E1). The main precipitation signals were above average rainfall in the eastern United States and northern Eurasia (Fig. E3).

 

a. North America

The 500-hPa circulation during May resembled a wavetrain pattern across North America with anomalous troughing over Alaska, ridging over Canada, and troughing over the North Atlantic Ocean (Fig. E9). Warmer than average temperatures were recorded across most of western Canada and the western United States, where many places reached the highest 70th percentile of occurrences (Fig. E1). Observed rainfall was recorded as near normal for most of North America except for the eastern U.S. and Alaska Panhandle (Fig. E3). Across the U.S., wetter than average conditions were recorded in the Great Plains, Midwest, Gulf Coast, Southeast, and Ohio Valley, where many areas exceeded the highest 90th percentile of occurrences (Figs. E5, E6). Drier than average conditions were observed in the Pacific Northwest, for the second consecutive month (Fig. E5).

 

b. Eurasia

The 500-hPa circulation during May resembled a wavetrain pattern across Eurasia with anomalous ridging over western Europe, troughing over eastern Europe, and ridging over western Russia (Fig. E9). Warmer than average conditions were observed in western and central Europe, as well as largely across Russia, with many areas recording temperatures in the highest 70th percentile of occurrences (Fig. E1). Cooler than average conditions were observed across Scandinavia and south toward the Black Sea (Fig. E1). Drier than average conditions were observed for France and neighboring regions, with much of the area recording rainfall in the lowest 10th percentile of occurrences (Fig. E3). Wetter than average conditions were observed across western and central Russia with many regions recording rainfall in the highest 90th percentile of occurrences (Fig. E3).

 

2. Southern Hemisphere

A near annular mode of below average 500-hPa height anomalies were featured around Antarctica during May along with strongly above average height anomalies south of South America (Fig. E15). Warmer than average conditions were observed across South America with many regions recording temperatures in the highest 90th percentile of occurrences (Fig. E1). Drier than average conditions were recorded across most of South America with many areas reaching the lowest 10th percentile of occurrences, continuing an extended drought in the region (Figs. E3, E4). Drier than average conditions were also recorded across the southern half of Australia with many areas reaching the lowest 10th percentile of occurrences (Fig. E3).