Extratropical
Highlights –February 2024
1. Northern Hemisphere
The 500-hPa circulation during
February resembled an anomalous wavetrain in quadrature
with four minima and maxima. Below-average height anomalies flanked both U.S.
coasts, the Norwegian Sea, and the Bering Sea (Fig. E9). Above-average height anomalies
were observed over most of Canada, the Mediterranean, Europe, the Middle East,
and the Sea of Japan (Fig. E9). The main land-surface temperature signals for
the month of February were dominated by widespread warmer than average
conditions to include above-average temperatures for most of North America,
Europe, and parts of Russia (Fig. E1). The main land-surface precipitation signals
include drier than average conditions for the Alaska Panhandle, parts of Canada
and the U.S., and wetter than average conditions in Northern Europe (Figs. E3, E4).
a. North America
The February
height pattern over North America was distinguished by anomalous troughing off both the west and east coasts of the U.S.,
and anomalous ridging over the Great Lakes region and northward to the Hudson
Bay in Canada (Fig. E9).
Alaska observed largely near-normal heights for the month of February with the
exception of below-average heights along the westernmost coast (Fig. E9). Nearly
all of North America recorded above-average temperatures for the month of
February. Many areas recorded temperatures in the highest 90th percentile of
occurrences (Fig. E1).
The overall precipitation pattern across the U.S. resembled a canonical
teleconnection pattern concurrent with moderate El Nino conditions. Wetter than
average conditions were recorded across most of California with Southern
California, and the Pacific Northwest, recording values in the highest 80th
percentile or higher, along with the Intermountain West (Figs. E3, E5, E6). Drier than average conditions were recorded for
much of the Upper Mississippi Valley with the Midwest recording precipitation
in the lowest 20th percentile of occurrences (Figs. E3, E5, E6).
b. Eurasia
Centered over
the Norwegian Sea, and north of the United Kingdom, anomalous troughing was observed during the month of February (Fig. E9).
Anomalous troughing was also recorded over central
Russia, and the coastal Koryak Mountains of eastern Russia (Fig. E9).
Conversely, to the south of the United Kingdom, anomalous ridging was observed
for the rest of Europe, the Mediterranean, and the Middle East (Fig. E9).
This pattern contributed to the strongly above-average rainfall in Northern
Europe where many areas recorded rainfall totals in the highest 90th percentile
of occurrences (Figs. E3, E4). The anomalous
ridging pattern in Southern Europe also contributed to the strongly
above-average temperatures recorded in the region, to include a large area from
France to Ukraine where temperatures were recorded in the highest 90th
percentile of occurrences (Fig. E1).
2. Southern Hemisphere
The 500-hPa pattern in the Southern
Hemisphere featured a center of anomalous troughing
over the polar latitudes and anomalous ridging over the adjacent middle
latitudes (Fig. E15).
A troughing minima was located over Wilkes Land in
Antarctica and a ridging maxima was located between South Africa and Queen Maud
Land in Antarctica (Fig. E15). Across much of South America, warmer than
average, and drier than average conditions were observed and both were recorded
in their respective highest 90th, and lowest 10th, percentile of occurrences (Figs. E1, E3, E4). Coastal areas of
Africa observed warmer than average temperatures and the southern half of
Africa observed drier than average conditions, while south of the Gulf of Aden,
and toward Lake Victoria, observed wetter than average conditions for the month
of February (Figs. E1,
E3, E4). The South
African monsoon season runs from October to April. During February, rainfall
was well below-average, reaching the lowest 10th percentile of occurrences for
southern Africa (Fig. E4). These dry conditions follow dry conditions in
the previous month (Fig. E4).