Extratropical Highlights – January 2023

 

1. Northern Hemisphere

The 500-hPa circulation during January resembled a combination of negative Pacific-North America (PNA) and negative Arctic Oscillation (AO) patterns which most notably resulted in a moderate below-average height anomaly centered over the U.S. West Coast.  Other features of the 500-hPa circulation include above-average heights south of Greenland, Scandinavia, and the Arctic Ocean, and below-average heights in eastern Russia (Fig. E9).  The main land-surface temperature signals during January include above-average temperatures across most of Europe, Canada, and the Eastern U.S., and below-average temperatures across Russia (Fig. E1).  The main precipitation signals were below-average rainfall around the Black Sea and Alaska Panhandle, and above-average precipitation for the U.S. West Coast and southern Europe (Fig. E3).

 

a. North America

The 500-hPa circulation over North America in January was characterized by below-average heights for the western U.S., and above-average heights across Canada and the Eastern Seaboard of the U.S. (Fig. E9).  This anomalous below-average height pattern contributed to exceptional rainfall totals for California, as well as the central U.S. and Mississippi Valley (Figs. E3, E5, E6).  Above-average temperature anomalies were in the 70th percentile and greater across all of Canada, Alaska, and the eastern half of the U.S. (Fig. E1).  Despite the above-average rainfall for California in the last two months, the region remains in a Moderate Drought category (according to the U.S. Drought Monitor) as a result of the below-average rainfall totals observed over the last 3 years.

 

b. Europe and Asia

The 500-hPa height anomalies featured a dipole pattern across Eurasia characterized by above-average heights over Scandinavia and below-average heights toward the east over Russia (Fig. E9).  This pattern contributed to the strong above-average temperature anomalies across most of Europe where temperatures were recorded in the 90th percentile of occurrences (Fig. E1). Below-average temperature anomalies were recorded in Russia (Fig. E1).  Above-average rainfall was recorded for the northwest region of Spain, southern Europe, Denmark and surrounding regions, and parts of central Russia, and below-average rainfall was recorded for the Black Sea and surrounding regions (Fig. E3).

 

2. Southern Hemisphere

The 500-hPa height pattern during January featured an annular mode with a center of below-average heights (Fig. E15).  Land-based temperature anomalies were largely near-normal for Africa, above-average for southern South America, and below-average for parts of the interior of Australia to include the Northern Territory (Fig. E1).  Precipitation anomalies were below-average for most of South America with the exception of regions in and near Columbia and Ecuador (Fig. E3).  In Australia, above-average precipitation anomalies were observed in both the Great Sandy Desert and Queensland territories (Fig. E3).  The South African monsoon season runs from October to April. This area received below-average rainfall for January (Fig. E4) while nearby Madagascar received above-average rainfall (Fig. E3).