Extratropical Highlights - April 2026

 

1. Northern Hemisphere

The 500-hPa circulation featured a high-latitude wavetrain pattern with a maxima in above average height anomalies over the North Pacific Ocean and a minima in below average height anomalies over the Canadian Maritime (Fig. E9). The main land-surface temperature signals include above average temperatures across most of the contiguous United States, western Europe, and western Asia (Fig. E1). The main precipitation signals include enhanced precipitation across central North America and eastern Europe and drier than average conditions in western Europe (Fig. E3).

 

a. North America

The 500-hPa height pattern across North America featured a tripole pattern with a maxima in height anomalies over the North Pacific Ocean, enhanced ridging over the eastern half of the contiguous United States, and a minima in height anomalies over the Canadian Maritime and Hudson Bay (Fig. E9). The anomalous troughing over the Hudson Bay ushered in cooler than average temperatures across central Canada, while the anomalous ridging to the south led to above average across the eastern United States, where many areas reached the highest 90th percentile of occurrences (Fig. E1). After record dry conditions across the western United States in March, precipitation totals in April were above average for the Pacific Northwest and Southern California, and near normal for the Inter-Mountain and Southwest regions (Fig. E5). Across the Midwest and Great Lakes, precipitation totals were well above normal with those areas exceeding the highest 90th percentile of occurrences (Figs. E3, E5). Drier than average conditions prevailed across the Northeast, Ohio Valley, Mid-Atlantic, Southeast, and Gulf Coast regions with parts of these regions reaching the lowest 10th percentile of occurrences (Figs. E3, E5, E6).

 

b. Eurasia

The 500-hPa height pattern across Eurasia featured a deamplifying wavetrain pattern with enhanced troughing across the North Atlantic Ocean, enhanced ridging over Scandinavia and Europe, followed by enhanced troughing over European Russia, and moderate ridging over Russia (Fig. E9). Under the two anomalous ridges, above normal temperatures were recorded across Europe and central Russia, with many areas reaching the highest 90th percentile of occurrences (Fig. E1). Drier than average conditions were recorded across Europe, where many areas reached the lowest 10th percentile of occurrences, while enhanced precipitation was recorded across European 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 enhanced ridging over the South Atlantic Ocean and Antarctica, and enhanced troughing over the Southern Ocean and adjacent Ross Sea (Fig. E15). Above average temperatures were recorded across most of South America, southern Africa, and southern Australia, and below average temperatures were recorded across northern Australia (Fig. E1). Drier than average conditions were recorded across Northeast Brazil, Southeast South America, and the majority of Australia, where many areas reached the lowest 10th percentile of occurrences (Figs. E3, E4). The South African monsoon season runs from October to April. April rainfall was well above normal (exceeding the 90th percentile) for the second month in a row. With the exception of drier than average conditions during the recent months of October and February, the end of the South African Monsoon season ends with an above average record (Figs. E3, E4).