Beginning with this
month, all anomalies reflect departures from the 1981-2010 base period.
500-hPa circulation during March featured above average heights over the central
North Pacific, Alaska, the southern United States, and northern Europe, and
below average heights over the western North Pacific, the Gulf of Alaska, the
southeastern North Atlantic, and the polar region (Fig.
E9). At 200-hPa, the circulation featured enhanced
troughs in both hemispheres over the tropical and subtropical central/eastern
Pacific (Fig. T22).
This pattern is consistent with the ongoing mature phase of La Niņa.
main surface temperature signals during March included well above average
temperatures across the south-central U.S., and eastern Siberia, and below
average temperatures across western and central Canada, and portions of western
China (Fig. E1). The main precipitation signals
included above average totals in the western and eastern U.S., and southern
Europe, and below-average totals along the U.S. Gulf Coast, northern Europe/
Scandinavia, and from northeastern China northeastward to southern Alaska (Fig. E3).
a. North Pacific
and North America
the lower latitudes, the 200-hPa circulation featured a 4-celled anomaly pattern
of streamfunction anomalies characterized by amplified ridges over Australasia
and amplified mid-Pacific troughs in both hemispheres (Fig.
T22). This circulation is linked to
the La Niņa- related pattern of tropical convection, with enhanced subtropical
ridges flanking the region of deep convection over Indonesia and the eastern
Indian Ocean, and the amplified troughs flanking the region of suppressed
convection over the central Pacific (Fig.
the extratropics, the mean 500-hPa circulation during March featured anomalous
ridging over the central North Pacific, Alaska, and the southern U.S., along
with deep troughs over both the western and eastern North Pacific (Fig.
E9). In western North America, the trough-ridge
couplet contributed a combination of well above average precipitation in the
western U.S. (Fig. E3),
and to well below average temperatures across western and central Canada (Fig. E1).
and precipitation patterns across the southern and eastern U.S. were strongly
influenced by the extensive area of above average heights across the south.
Prominent signals included exceptionally warm and dry conditions in the
south-central U.S. and northern Mexico, along with continued well below average
precipitation across the U.S. Gulf Coast (Fig.
E5). Significant monthly rainfall deficits have
prevailed across this region since October 2010. This signal is consistent with
La Niņa. Farther north, increased storminess and a series of major frontal
passages contributed to above average precipitation extending from central
Alabama northward to Maine (Fig. E6).
500-hPa circulation during March featured a 3-celled pattern of height
anomalies, with above average heights across northern Europe flanked by negative
anomalies to the north and south (Fig. E9).
This pattern was associated with enhanced southwesterly winds across Scandinavia
and northwestern Russia, and with increased storminess across southern Europe
and northwestern Africa. These conditions mainly affected the precipitation
patterns, which featured above average precipitation across southern Europe, and
exceptionally dry conditions across northern Europe, southern Scandinavia, and
northwestern Russia (Fig. E1).
For northern Europe, area-averaged totals were the lowest for March dating back
to 1979 (Fig. E5).
the past two months, the 500-hPa circulation over northern Russia and Siberia
has featured a trough in the west and a ridge in the east, accompanied by a deep
southwesterly flow of marine air into the high latitudes of the Eurasian
continent (Figs. E9, E10).
These conditions led to an early snow-melt and well above average temperatures
during March across most of Siberia.
during March, precipitation was well below average from eastern China
northeastward to eastern Siberia. This dryness was associated with upper-level
convergence (Fig. T23) that was focused in
the area between the upstream amplified upper-level ridge and the downstream
amplified trough (Fig. E9).
Another contributing factor was a southeastward shift of the East Asian jet
core, with much of the entire region also situated in enhanced sinking motion
within the amplified left jet entrance region (Fig.
anomalies reflect departures from the 1981-2010 base period.
500-hPa circulation during March featured above average heights across the
central South Pacific and over the southern Atlantic Ocean, and below average
heights over the high latitudes of the eastern South Pacific (Fig.
E15). In the subtropics, the upper-level
(200-hPa) streamfunction pattern reflected an amplified trough across the
central South Pacific, and an amplified ridge over Australia (Fig.
T22). These overall circulation
anomalies are consistent with La Niņa.
precipitation signals during March reflected above average totals across most of
Australia, but with well below average totals in the extreme southwest (Fig.
E3). Much of central and western Australia also
recorded significantly below average temperatures during the month, with large
portions recording departures in the lowest 10th percentile of
occurrences (Fig. E1).
The South African
rainy season lasts from October to April. During March, rainfall for the region
as a whole was slightly above average. Totals were mainly above average in the
western part of the monsoon region and below average in Mozambique (Fig.
E4). A similar east-west dipole pattern was also
evident during February. This pattern has been associated with a persistent
anticyclonic circulation (Fig. T22)
and upper-level divergence (Fig. T23)
over the western part of the monsoon region, and with upper-level convergence
and large-scale sinking motion farther east in the area immediately downstream
of the mean ridge axis.