1. Northern Hemisphere
500-hPa circulation during March featured above-average heights at high
latitudes and in the subtropics, and below average heights in the middle
latitudes (Fig. E9). This hemispheric scale pattern
of anomalies projected strongly onto several leading modes of variability (Table E1, Fig. E7),
including the negative phases of the North Atlantic Oscillation (NAO) and the
East Pacific/Central Pacific (EP-NP) pattern, and the positive phases of the
East Atlantic (EA), West Pacific (WP), and Pacific/North American (PNA)
patterns. The NAO, EA, and PNA patterns have been exceptionally prominent and
persistent since July 2009.
circulation features during March included anomalous ridges over the central
North Pacific, central Canada, and Greenland, and anomalous troughs over the
Gulf of Alaska, from the southeastern U.S. to southern Europe, and over
Scandinavia/ northwestern Russia. These anomalies were associated with a
significantly weaker than average Hudson Bay trough, high-latitude blocking over
the Atlantic sector, and a pronounced southward shift of the mean jet stream
over the Atlantic Ocean (Fig. T21).
main temperature signals during March included above average temperatures across
Canada, and below average temperatures in the southeastern U.S. and portions of
eastern Scandinavia and northwestern Russia (Fig.
E1). The main precipitation signals included
above-average totals in western Canada and southwestern Europe, and below
average totals in eastern Canada and the U.S. Gulf Coast (Fig. E3).
a. North Pacific/
extratropical circulation during March featured a 4-celled pattern of 500-hPa
height anomalies across the North Pacific and North America, with above average
heights over the central North Pacific and Canada, and below average heights
over the eastern North Pacific and southeastern U.S. (Fig.
anomaly pattern projected onto three leading modes of variability, including the
negative phase of the East Pacific/Central Pacific (EP-NP) pattern, and the
positive phases of the West Pacific (WP) and Pacific/North American (PNA)
patterns. A positive PNA pattern has prevailed since July 2009, and is
consistent with the ongoing El Niņo. Over
North America, aspects of this persistent PNA pattern during March included
amplified troughs over the eastern North Pacific and the southeastern United
States, and a weaker than average strength of the mean Hudson Bay trough.
conditions again contributed to above average temperatures in Canada, with much
of the country recording departures in the upper 90th percentile of
occurrences (Fig. E1).
They also contributed to well below average temperatures along the U.S. Gulf
Coast and in the Gulf of Mexico, where SST departures were in the lowest 10th
percentile of occurrences. Much of North America recorded near average
precipitation during March, with below average totals observed in the Gulf Coast
and eastern Canada (Fig. E3).
March, a 3-celled pattern of 500-hPa height anomalies dominated the North
Atlantic and Europe (Fig. E9).
This pattern featured above average heights at high latitude and in the
subtropics, and below average heights across the central North Atlantic. These
anomalies projected strongly onto the negative phase of the NAO and the positive
phase of the EA pattern (Table E1,
Fig. E7). These patterns have been remarkably
persistent, with March marking the sixth consecutive month with a large negative
NAO index and the ninth consecutive month with a large positive EA index.
March, regional aspects of these signals included a blocking ridge at high
latitudes and a deep trough extending from the southeastern U.S. to southeastern
Europe (Fig. E9). These conditions were associated
with a pronounced southward shift and zonal elongation of the North Atlantic jet
stream, with the main jet axis extending from the U.S. Gulf Coast to northern
Africa (Fig. T21).
2. Southern Hemisphere
The 500-hPa circulation during March featured above average heights over
Antarctica and most of the extratropical South Pacific Ocean, and below average
heights in the area south of New Zealand (Fig. E15). Regionally, an anomalous
upper-level trough (Fig. T22)
and lower-level moisture convergence contributed above average precipitation in
eastern Australia (Fig. E3).
Much of Argentina recorded well above average temperatures during the month,
with many areas recording departures in the upper 90th percentile of
In southern Africa, the rainy season lasts from October to April. During March,
rainfall was generally near average across the region. Totals have been near
average since January, and were well below average in only one month- December.
The South African rainy season is often below average during El Niņo.