Extratropical
Highlights -- May 2022
1. Northern Hemisphere
The 500-hPa
circulation during May featured several wave patterns, including for the
Western Hemisphere, a canonical response to La Nina, with some damping of that
pattern due to a negative Pacific North America (PNA) pattern, an anomalous
wave pattern across Europe and North Asia, and an anomalous wave pattern arcing
over the North Pole (Figs. E7, E9).
The main land-surface temperature signals were above-average
temperatures across the southern tier of the United States and Mexico, as well
as Europe and Central Asia (Fig. E1). The main precipitation signals were
above-average rainfall in South Asia, parts of North America and Russia, and
below-average rainfall for Europe and parts of North America (Fig. E3).
a.
North America
The anomalous height pattern over North America for the
month of May featured above-average heights over western Alaska, the Aleutian
Islands, southern California, the Gulf of California, eastern Canada, and the
U.S. Midwest and Northeast, and below-average height anomalies over western
Canada, the Gulf of Alaska, the Pacific Northwest and north-central U.S. (Fig. E9). The
pattern contributed to above-average temperature anomalies for the southern
tier of the U.S. and Mexico, as well as the eastern half of the U.S. and
Canada, where percentiles reached the 90th percent of occurrences for some
regions (Fig. E1).
Moderately above-average temperature anomalies were observed in Alaska as
well. Below-average temperature anomalies
were observed for parts of western Canada and the Pacific Northwest region of
the U.S, where percentiles reached the 30th percent of occurrences (Fig. E1). The
anomalous below-average heights in the Pacific Northwest ushered in
above-average precipitation anomalies for that region, as well as for central
Canada and Quebec (Figs. E1). The central U.S. and Northern Plains also
observed above-average rainfall leading to improvements in the drought
conditions for those areas, according to the U.S. Drought Monitor, however,
Texas and the Southwest observed below-average rainfall for the month of May,
leading to a degradation of drought conditions (Fig. E6).
b.
Eurasia
An anomalous wave pattern across Eurasia brought
above-average heights to Europe and central Russia, which straddled anomalous
below-average heights over western Russia (Fig.
E9). The anomalous height pattern across Eurasia
ushered in above-average temperatures for Europe and central Russia, and a
slight tilt toward below-average temperatures in western Russian (Fig. E1). Above-average
temperatures reached the 90th percentile across much of Europe and central
Asia. Below-average rainfall was observed in Europe and above-average rainfall
was observed for much of southern Asia and western Russia, with anomalies
reaching the 90th percentile in many areas (Fig. E3).
2.
Southern Hemisphere and Africa
The 500-hPa circulation during May featured an annular mode
of above-average height anomalies adjacent to Antarctica and over the South
Pacific Ocean and below-average heights in the center of the above-average
height anomalies (Fig. E15).
Observed temperatures in Australia were near-normal for most of the
interior and above-average for northern and eastern coastal areas (Fig. E1). Observed precipitation was also near-normal
for much of Australia with above-average rainfall observed along the coast of
Queensland and below-average rainfall observed along the southern coast of
Western Australia (Fig. E3). Below-average rainfall was observed for much of
South America (Fig. E3)
with SE South America reaching the lower 40th percentile of occurrences (Fig. E4).
Both the Sahel of Africa and South Africa observed rainfall that exceeded the
80th percentile of occurrences (Figs. E3, E4), while east of the Congo, from Sudan to
Tanzania, below-average rainfall was observed, reaching the lowest 10th
percentile in some areas (Fig. E3). Temperature anomalies were largely near-normal
for much of the African continent with the exception of the Sahel and east of the
Congo, where above-average temperature anomalies reached the 70th percentile (Fig. E1).