Extratropical
Highlights – January 2024
1.
Northern Hemisphere
The 500-hPa circulation during January resembled a weak
negative Arctic Oscillation (AO) teleconnection pattern with above-average
heights over the Polar region and below-average heights in the middle latitudes
(Fig. E9). The main land-surface
temperature signals include above-average temperatures across most of Europe,
Asia, eastern Canada, and the western U.S. (Fig. E1). The main precipitation signals
include above-average rainfall in the eastern U.S. and eastern
Europe (Fig. E3).
a. North America
The 500-hPa circulation over North America in January was
characterized by above-average heights over the eastern half of Canada and
Alaska, and slightly below-average heights over the central U.S. (Fig. E9). For
much of the U.S., temperature anomalies were largely near normal with the
exception of the Pacific Northwest where temperatures were above normal with
some areas recording anomalies in the highest 90th percentile of
occurrences. In eastern Canada,
temperature anomalies were above normal with a large area recording values in
the highest 70th percentile of occurrences (Fig. E1). The eastern half of the U.S.
recorded above-average rainfall with a large area reaching the highest 90th
percentile of occurrences and many areas seeing a Class 1 Improvement in
drought conditions, according to the U.S. Drought Monitor. The Great Lakes and
Midwest recorded rainfall in the 90th percentile or greater during January,
after a previous 4 months of below-average rainfall (Figs. E3, E5 E6). The Pacific Northwest also recorded wetter than
average conditions with some areas reaching 175% of normal (Figs. E3, E5, E6).
b. Europe and Asia
The 500-hPa height anomalies featured below-average heights
over central Russia and above-average heights over eastern Russia and southern
Europe (Fig. E9).
Temperatures were above normal across southern Eurasia and central Russia with
many areas recording values in the upper 70th and 90th percentile of
occurrences (Fig. E1).
The strongest anomalies were in a widespread area located in central Russia (Fig. E1). Central
and southern parts of Scandinavia recorded below-average temperatures (Fig. E1). The
majority of Eurasia recorded near normal precipitation anomalies. Eastern
Europe recorded precipitation in the upper 70th and 90th percentile of
occurrences (Fig. E3).
2.
Southern Hemisphere
The 500-hPa height pattern during January featured
below-average heights over the Polar region and above-average heights in the
middle latitudes. Temperatures across
South America were above-average with many areas recording values in the
highest 90th percentile of occurrences.
Near the coasts in Africa, temperatures were above-average, and along
the eastern region of Australia, temperatures were also recorded at
above-average values (Fig. E3). Most of South America experienced drier than
average conditions during January (Figs.
E3, E4). Drier than
average conditions were recorded for western portions of central Africa with
the Democratic Republic of Congo and Gabon recording values in the lowest 10th
percentile of occurrences (Fig. E3). The eastern portion of Africa recorded
above-average rainfall in areas such as Tanzania, Kenya, and Uganda where
values reached the highest 90th percentile of occurrences (Fig. E3). Precipitation anomalies were also
elevated in the eastern half of Australia where areas recorded precipitation in
the highest 70th percentile of occurrences (Fig. E3). The South African monsoon
season runs from October to April. This area received below-average rainfall
for January with values recorded in the lowest 20th percentile of occurrences (Fig. E4).