Extratropical Highlights

  Table of Indices  (Table 3)

  Global Surface Temperature  E1

  Temperature Anomalies (Land Only)  E2

  Global Precipitation  E3

  Regional Precip Estimates (a)  E4

  Regional Precip Estimates (b)  E5

  U.S. Precipitation  E6

  Northern Hemisphere

  Southern Hemisphere

  Stratosphere

  Appendix 2: Additional Figures

Extratropical Highlights

MARCH 2010

1. Northern Hemisphere

The 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.

Regional 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).

The 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/ North America

The 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. E9).  This 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 Niño.  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.                 

These conditions again contributed to above average temperatures in Canada, with much of the country recording departures in the upper 90^th 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 10^th 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).

b. Europe

During 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.

During 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 occurrences.