Extratropical Highlights – January 2025

 

1. Northern Hemisphere

The 500-hPa circulation during January featured widespread above average height anomalies with a maxima in anomalies over the North Pacific Ocean, the Sea of Okhotsk, central Eurasia, and Greenland, and a minima in height anomalies over the North Atlantic Ocean (Fig. E9). The main land-surface temperature signals include above average temperatures across most of northern North America and Eurasia, and below average temperatures across southern North America (Fig. E1). The main precipitation signals include below average rainfall along the eastern and western coasts of North America, and above average rainfall in western Europe and western Russia (Fig. E3).

 

a. North America

The 500-hPa circulation over North America in January was characterized by a dipole pattern. Above average height anomalies were centered over the North Pacific Ocean and spread over Alaska, western Canada, and the western one-third of the U.S., while below average heights stretched from the North Atlantic Ocean to cover most of the eastern half of the U.S. and eastern Canada (Fig. E9). This anomalous height pattern contributed to largely below average temperatures across most of the U.S., with many areas reaching the lowest 30th percentile of occurrences, and above average temperatures across most of Canada and Alaska, where many areas reached the highest 70th percentile of occurrences (Fig. E1). Drier than average conditions were recorded along both the west and east coasts of North America, with many areas reaching the lowest 10th percentile of occurrences, while above average rainfall was recorded in southern Alaska (Figs. E3, E5 E6). Drier than average conditions have prevailed for at least the last four months in the Gulf Coast, Southeast, Ohio Valley, Mid-Atlantic, Northeast, and Southwest regions of the U.S. (Fig. E5).

 

b. Europe and Asia

The 500-hPa height anomalies in January were predominantly above average across most of Eurasia (Fig. E9). Above average temperatures were recorded across nearly all of Eurasia, with many areas reaching the highest 90th percentile of occurrences (Fig. E1). Below average temperatures were recorded for the regions in contact with the Baltic Sea, where some areas recorded temperatures in the lowest 10th percentile of occurrences (Fig. E1). Near normal precipitation was recorded for the majority of Europe and Asia (Fig. E3). The northwestern and central portions of Siberia recorded above average rainfall, with several areas reaching the highest 90th percentile of occurrences (Fig. E3). Rainfall amounts were above average in the western half of Spain (Fig. E3).

 

2. Southern Hemisphere

The 500-hPa height pattern during January resembled a wavetrain pattern with a maxima in height anomalies over the South Pacific Ocean and minima in height anomalies over the South Atlantic and Indian Oceans (Fig. E15). Above average temperatures were widely recorded, with many areas reaching the highest 90th percentile of occurrences (Fig. E1). Drier than average conditions were recorded across nearly all of South America, continuing an extended drought in Northeast Brazil and Southeast South America (Figs. E3, E4). Australia recorded below average rainfall for the interior portion of the country, and above average rainfall along the western and northeastern coasts (Figs. E3, E4). The South African monsoon season runs from October to April. This area received above average rainfall during January with many areas exceeding the highest 70th percentile of occurrences (Figs. E3, E4).