Extratropical Highlights – April 2022

 

1. Northern Hemisphere

The 500-hPa circulation features during April resembled a combination of wintertime La Niña and negative Pacific North America (PNA) teleconnection patterns (Figs. E7, E9).  Moderate above-average height anomalies were observed over the North Pacific Ocean, Eurasia, and Siberia, with strong above-average height anomalies observed over the Arctic Ocean and off the southeast coast of Greenland (Fig. E9).  Moderate below-average height anomalies were observed across central North America, the North Atlantic Ocean, Scandinavia, and eastern Siberia (Fig. E9).

The main land-surface temperature signals during April included above-average temperatures for most of Asia, western Alaska, and southern U.S., and below-average temperature across most of Canada (Fig. E1).  The main precipitation signals during April were above-average rainfall totals in parts of North America, eastern Eurasia, and Siberia, and below-average rainfall totals for the Alaskan Panhandle, Central U.S., and the U.S. Gulf states (Fig. E3).

 

a. North America

The anomalous height pattern for April matched with a canonical wintertime La Niña teleconnection pattern bringing in below-average temperatures for Canada and along the Canada and U.S. border while the southern half of the U.S. experienced above-average temperatures (Fig. E9).  Above-average temperatures were also recorded for the Seward Peninsula and surrounding areas in Alaska (Fig. E9).  Predominantly near-normal rainfall totals were observed for much of Alaska, Canada, and the U.S.  Areas near Manitoba and Quebec in Canada observed above-average precipitation while a small region in the Central U.S., along the Gulf Coast, and the Alaskan Panhandle recorded drier than average rainfall totals (Fig. E3).

 

b. Eurasia

The widespread above-average 500-hPa height anomalies for April across much of Asia contributed to widespread observations of above-average temperatures for the region, with some areas recording temperatures in the 90th percentile of occurrences (Fig. E1).  Above-average temperatures were also predominant in the western parts of France and the United Kingdom (Fig. E1). Near-normal precipitation totals were recorded for most of Europe and Asia (Fig. E3).  Some localized exceptions include above-average rainfall for Belarus and surrounding regions, regions to the north of Mongolia, and eastern Siberia (Fig. E3).  Areas near-to and south of Kazakhstan observed below-average rainfall totals with those totals in the lower 30th percentile of occurrences (Fig. E3).

 

2. Southern Hemisphere

The 500-hPa height pattern for the month of April resembled the positive phase of the Southern Annular Mode (SAM) with nearly a complete "ring" of above-average height anomalies along the middle-latitudinal band (Fig. E15). The features of this mode included moderate above-average heights for New Zealand with two maxima centered off the west coast of Chile and South Atlantic Ocean (Fig. E15).  Moderate below-average height anomalies were observed north of the Ross Sea, the southern region of South America, and parts of Antarctica (Fig. E15).  Above-average temperatures were recorded for most of central and eastern Australia and New Zealand, with regions in and near-to the Northern Territory of Australia recording temperatures in the 90th percentile of occurrences (Fig. E1).  The most notable precipitation signals for the month of April were widespread above-average rainfall totals for regions in central and southern Africa, and below-average rainfall totals observed across much of north and central South America (Fig. E3).  These regions experienced departures from average that met and exceeded the 90th percentile of occurrences (Fig. E3).  The South African monsoon season runs from October to April. Observed April rainfall exceeded recorded totals during March, with April totals reaching 400-mm or more and in the 100th percentile of occurrences (Figs. E3, E4).