Extratropical Highlights -- May 2024

 

1. Northern Hemisphere

The 500-hPa circulation during May featured anomalous ridging over the North Pacific Ocean, northern Canada, Scandinavia, and the Taimyr Peninsula of Russia, and anomalous troughing over Greenland, the Bering Strait, central Canada, and the Kara Sea (Fig. E9). Some features of the anomalous height pattern resemble a canonical negative Pacific-North American (PNA) teleconnection pattern, which was strongly negative during the month of May (Fig. E7). The main land-surface temperature signals were above average temperatures across much of the southern and eastern regions of North America, Europe, and central Eurasia (Fig. E1). The main precipitation signals were above average rainfall in North America, Europe, and in certain areas across Eurasia, and below average rainfall in Finland and eastern Europe (Fig. E3).

 

a. North America

The anomalous height pattern over North America for the month of May featured weakly below average heights over the central region of the country and the western half of Alaska, and strongly above average heights in the Northwest Territories province of Canada (Fig. E9). The weak trough pattern contributed to near-normal to slightly below normal temperatures across much of Canada, Alaska, and the northwest quarter of the U.S. (Fig. E1). Above average temperatures were recorded across the southern tier and eastern half of the U.S. where many areas reached the highest 90th percentile of occurrences (Fig. E1). Precipitation totals were above average across central and eastern Canada, as well as from the Upper Mississippi Valley to the Southeast U.S. (Fig. E3).

 

b. Eurasia

A tripole pattern of height anomalies across the northern region of Eurasia contributed to a tripole pattern of anomalous surface temperatures (Figs. E1, E9). Above average temperatures were recorded for the United Kingdom, southern regions of Scandinavia, northern Europe, and across central Russia, Mongolia, and China, where these areas recorded temperatures in the highest 90th percentile of occurrences (Fig. E1). Below average temperatures were recorded west of the Ural Mountains in Russia and eastern Europe (Fig. E1). Wetter than average conditions were recorded across central Europe with some regions, including Switzerland and Austria, reaching the highest 90th percentile of occurrences (Figs. E3, E4). Drier than average conditions were observed across Scandinavia and to regions south near the Black Sea where many areas reached the lowest 10th percentile of occurrences (Fig. E3). Wetter than average conditions were recorded across the western half of Russia, the Taimyr Peninsula, across western China, Kazakhstan, and north of the Yellow Sea in Manchuria, China (Figs. E3, E4).

 

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 Australia and south of South America (Fig. E15). Above average temperatures were recorded across the northern half of South America, west Africa, South Africa, and along the southern sections of the Western Australia territory (Fig. E1). Below average temperatures were recorded across the southern half of South America (Fig. E1). Drier than average conditions were recorded across most of South America with many areas reaching the lowest 10th percentile of occurrences, and only a small area near Uruguay recorded wetter than average conditions for the month of May (Figs. E3, E4). Drier than average conditions were recorded in central Africa and southern Australia, where many areas reached the lowest 10th percentile of occurrences (Figs. E3, E4).