Extratropical Highlights – April 2025

 

1. Northern Hemisphere

The 500-hPa circulation featured several centers of above average height anomalies across the Northern Hemisphere and a smaller area of below average height anomalies centered over the Kara Sea (Fig. E9). The main land-surface temperature signals include widespread above average anomalies across North America, Europe, and Asia (Fig. E1). The main precipitation signals include wetter than average conditions in eastern North America and central Eurasia (Fig. E3).

 

a. North America

The height pattern across North America featured above average anomalies along both coasts and centrally located near normal anomalies (Fig. E9). Temperatures were above average, or near average, with most of Alaska and the U.S. West Coast, recording temperatures in the highest 70th percentile of occurrences, and the eastern third of the U.S. recording temperatures in the highest 90th percentile of occurrences (Fig. E1). Wetter than average conditions were recorded in the eastern U.S., with several areas reaching the highest 90th percentile of occurrences (Fig. E3).

 

b. Eurasia

The height pattern resembled a wavetrain pattern with above average heights centered over Northern Europe, below average heights over north-central Russia, and above average heights over eastern Russian (Fig. E9). Temperatures were largely above average across Eurasia with many areas reaching the highest 90th percentile, including all of Europe (Fig. E1). Drier than average conditions were recorded in Northern Europe and above average rainfall was recorded across most of Russia, with many areas reaching the highest 90th percentile of occurrences (Figs. E3, E4).

 

2. Southern Hemisphere

The 500-hPa circulation featured a wavetrain pattern with above average heights south of South America, below average heights south of Africa, above average heights south of Australia and the South Pacific Ocean, and below average heights southeast of South America (Fig. E15). Temperatures across South America, southern Africa, and the interior of Australia were largely near normal with a few regions in South America and coastal Australia reaching the highest 70th and 90th percentiles of occurrences (Fig. E1). Rainfall totals were well below average for much of South America, continuing an extended period of drought (Figs. E3, E4). Wetter than average conditions were recorded across southern Africa with many areas reaching the highest 90th percentile of occurrences (Figs. E3, E4). The South African monsoon season runs from October to April. After slightly above average rainfall during the month of March, rainfall in April exceeded the 90th percentile. Overall, the South African monsoon season averaged out to record above average rainfall (Fig. E4).