Extratropical Highlights -- May 2023

 

1. Northern Hemisphere

The 500-hPa circulation during May featured a wave pattern of above- and below-average height anomalies, with predominantly above-average height anomalies over Canada, the North Pacific Ocean, and northern Eurasia, and below-average anomalies centered over the North Pole (Fig. E9).  The main land-surface temperature signals were above-average temperatures across much of North America and central Eurasia (Fig. E1).  The main precipitation signals were below-average rainfall in North America, Europe, and Russia (Fig. E3).

 

a. North America

The anomalous height pattern over North America for the month of May featured strong above-average height anomalies (Fig. E9). This pattern contributed to strongly above-average temperature anomalies across much of Canada and the U.S. with many areas exceeding the 90th percentile of occurrences (Fig. E1). Precipitation anomalies were below-average for the eastern half of North America and British Columbia, and above-average across the U.S. Central Plains (Figs. E5, E6).

 

b. Eurasia

The anomalous height pattern over Eurasia featured above-average heights over Europe and western Russia (Fig. E9). This pattern contributed to the above-average temperatures recorded for both Europe and western Russia, with areas in Russia reaching the 90th percentile of occurrences (Fig. E1). Below-average rainfall was recorded for Northern Europe and central Russia, and above-average rainfall was recorded for Southern Europe (Figs. E3, E4).

 

2. Southern Hemisphere

The 500-hPa circulation during May featured an annular wave train pattern with regions of alternating above- and below-average height anomalies (Fig. E15). Above-average temperatures were recorded in parts of South America, including most of the western coast countries, and below-average temperatures were recorded for much of Australia with some areas reaching the lowest 10th percentile of occurrences (Fig. E1). Drier than average conditions were observed for much of South America, central regions of Africa, and across most of Australia with many of these areas recording precipitation in the lowest 10th percentile of occurrences (Fig. E3).