Extratropical Highlights
– March 2014
1. Northern Hemisphere
The 500-hPa circulation during March
featured above-average heights over the central North Atlantic, Europe, and
eastern Asia, and below-average heights over eastern Canada, the high latitudes
of the North Atlantic, and northwestern Russia (Fig. E9). Over the North Atlantic, the
500-hPa height anomalies projected onto the positive phase of the East Atlantic
(EA, +0.92) teleconnection pattern (Table
E1, Fig. E7). A strong
positive EA pattern has been present for the last four months.
The main land-surface temperature signals
during March included above-average temperatures in the southwestern U.S.,
Mexico, and throughout nearly all of Eurasia, and below-average temperatures across
Canada and the eastern half of the U.S. (Fig.
E1). The main precipitation signals included above-average
totals in the Pacific Northwest and Northeast regions of the U.S., and below-average
totals in the central U.S. and in most of Europe (Fig. E3).
a. North Pacific/ North America
The mean 500-hPa circulation during
March featured an amplified Hudson Bay trough (Fig. E9). This pattern was associated
with anomalous northerly and northwesterly flow across Canada and the
northeastern quadrant of the U.S. (Fig. E10), resulting in below-average temperatures across
both regions (Fig. E1).
Precipitation during March was well
above-average in the Pacific Northwest U.S., with many locations recording
totals in the upper 90th percentile of occurrences (Fig. E3).
This marks the second straight month for well above-average totals in that
region (Fig. E5).
Precipitation was also above average in both the northeastern and mid-Atlantic
regions of the U.S. during March, with both areas recording above-average
totals in each of the last three months (Fig.
E5).
In contrast, the central U.S.
received well below-average precipitation during March, with portions of the Great
Plains recording totals in the lowest 10th percentile of
occurrences. The Great Plains region has recorded below-average precipitation
for the past five months (Fig. E5), leading
to an expansion and worsening of drought conditions. According to the
U.S. Drought Monitor (http://droughtmonitor.unl.edu),
severe or extreme drought was present from central Texas to northern Nebraska by
the end of March, with portions of the Texas Panhandle and western Oklahoma
experiencing exceptional drought. Much of California and northwestern Nevada also
reported either extreme or exceptional ongoing drought throughout the month. Southern
Oregon, southern Idaho, and much of New Mexico reported ongoing severe drought.
b. North Atlantic/ Eurasia
The mean 500-hPa circulation during
March featured above-average heights across the central North Atlantic, Europe,
and eastern Asia, and below-average heights over northwestern Russia (Fig. E9). This
pattern projected onto the positive phase of the East Atlantic (+0.92) teleconnection pattern (Table E1, Fig. E7).
March marks the fourth consecutive with a strong positive EA pattern.
The circulation during March also
featured a strong split-flow pattern over the eastern North Atlantic, with an enhanced
southwesterly flow of mild marine air throughout Europe and northern Russia. These
conditions contributed to above-average temperatures across Eurasia, with much
of the continent recording departures in the upper 70th and upper 90th
percentile of occurrences (Fig. E1). The strong ridge over Europe also contributed
to well below-average precipitation across central and Northern Europe, with
many areas recording totals in the lowest 10th percentile of
occurrences (Fig. E3).
The Northern Europe sector has recorded large precipitation deficits in seven
of the last nine months (Fig. E4).
2. Southern Hemisphere
The mean 500-hPa circulation during
March featured above-average heights across the high latitudes of the South
Pacific, and both the central South Atlantic and Indian Oceans, and below-average
heights south of Africa (Fig. E15).
In Australia, precipitation was below
average across much of the continent, with the largest deficits recorded in the
northeast (Fig. E3).
March is the second straight month with large precipitation deficits in that
region.
The South African rainy season lasts
from October to March. Precipitation across the region was varied during March,
with some interior locations recording totals in the upper 90th
percentile of occurrences, and both Madagascar and southeastern Africa
recording totals in the lowest 30th percentile of occurrences (Fig. E3). To
date, area-averaged totals for the 2013-14 rainy season
were above-average during October, December, January and March, below-average
in November, and near-average in April.
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