Extratropical Highlights -- May 2022

 

1. Northern Hemisphere

The 500-hPa circulation during May featured several wave patterns, including for the Western Hemisphere, a canonical response to La Nina, with some damping of that pattern due to a negative Pacific North America (PNA) pattern, an anomalous wave pattern across Europe and North Asia, and an anomalous wave pattern arcing over the North Pole (Figs. E7, E9).

The main land-surface temperature signals were above-average temperatures across the southern tier of the United States and Mexico, as well as Europe and Central Asia (Fig. E1). The main precipitation signals were above-average rainfall in South Asia, parts of North America and Russia, and below-average rainfall for Europe and parts of North America (Fig. E3).

 

a. North America

The anomalous height pattern over North America for the month of May featured above-average heights over western Alaska, the Aleutian Islands, southern California, the Gulf of California, eastern Canada, and the U.S. Midwest and Northeast, and below-average height anomalies over western Canada, the Gulf of Alaska, the Pacific Northwest and north-central U.S. (Fig. E9). The pattern contributed to above-average temperature anomalies for the southern tier of the U.S. and Mexico, as well as the eastern half of the U.S. and Canada, where percentiles reached the 90th percent of occurrences for some regions (Fig. E1). Moderately above-average temperature anomalies were observed in Alaska as well.  Below-average temperature anomalies were observed for parts of western Canada and the Pacific Northwest region of the U.S, where percentiles reached the 30th percent of occurrences (Fig. E1). The anomalous below-average heights in the Pacific Northwest ushered in above-average precipitation anomalies for that region, as well as for central Canada and Quebec (Figs. E1). The central U.S. and Northern Plains also observed above-average rainfall leading to improvements in the drought conditions for those areas, according to the U.S. Drought Monitor, however, Texas and the Southwest observed below-average rainfall for the month of May, leading to a degradation of drought conditions (Fig. E6).

 

b. Eurasia

An anomalous wave pattern across Eurasia brought above-average heights to Europe and central Russia, which straddled anomalous below-average heights over western Russia (Fig. E9). The anomalous height pattern across Eurasia ushered in above-average temperatures for Europe and central Russia, and a slight tilt toward below-average temperatures in western Russian (Fig. E1). Above-average temperatures reached the 90th percentile across much of Europe and central Asia. Below-average rainfall was observed in Europe and above-average rainfall was observed for much of southern Asia and western Russia, with anomalies reaching the 90th percentile in many areas (Fig. E3).

 

2. Southern Hemisphere and Africa

The 500-hPa circulation during May featured an annular mode of above-average height anomalies adjacent to Antarctica and over the South Pacific Ocean and below-average heights in the center of the above-average height anomalies (Fig. E15).  Observed temperatures in Australia were near-normal for most of the interior and above-average for northern and eastern coastal areas (Fig. E1).  Observed precipitation was also near-normal for much of Australia with above-average rainfall observed along the coast of Queensland and below-average rainfall observed along the southern coast of Western Australia (Fig. E3). Below-average rainfall was observed for much of South America (Fig. E3) with SE South America reaching the lower 40th percentile of occurrences (Fig. E4). Both the Sahel of Africa and South Africa observed rainfall that exceeded the 80th percentile of occurrences (Figs. E3, E4), while east of the Congo, from Sudan to Tanzania, below-average rainfall was observed, reaching the lowest 10th percentile in some areas (Fig. E3). Temperature anomalies were largely near-normal for much of the African continent with the exception of the Sahel and east of the Congo, where above-average temperature anomalies reached the 70th percentile (Fig. E1).