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 2009

1. Northern Hemisphere

The 500-hPa height field during March 2009 featured a wave-1 pattern with generally positive anomalies in the Western Hemisphere and negative anomalies in the Eastern Hemisphere (Fig. E9). Notable departures from this pattern included persistent negative anomalies over western Canada and positive anomalies over south-central Russia . Across the Pacific Ocean and North America , the circulation reflected a pronounced westward retraction of the East Asian jet stream (Fig. T21), along with a westward shift of the downstream ridges and troughs. These conditions are consistent with La Nina.

The main temperature signals during March generally reflected the anomalous upper-level circulation, with above average temperatures across the southern half of the United States and central Asia , and below average temperatures in western Canada (Fig. E1). The main precipitation signals included above-average totals in southwestern Canada , portions of the U.S. Gulf Coast, and eastern Europe, and below-average totals in northwestern Europe and Scandinavia (Fig. E3).

a. North Pacific/ North America

At 200-hPa, La Niña again contributed to a pronounced inter-hemispheric symmetry of the circulation anomalies across the Pacific Ocean . In the subtropics, aspects of this circulation included enhanced mid-Pacific troughs in both hemispheres flanking the suppressed equatorial convection, and a westward retraction of the subtropical ridges to Australasia (Fig. T22). Associated with this pattern, the East Asian jet stream was retracted westward toward the western Pacific (Fig. T21). These conditions contributed to a westward shift to the central North Pacific of the mean ridge normally located over western North America , and a westward shift of the mean Hudson Bay trough to western North America (Fig. E9). The associated storm track was also highly anomalous, with increased storminess extending across the Gulf of Alaska into western North America , and significantly decreased storminess across the northeastern United States (Fig. E13).

These conditions were associated with a dipole pattern of temperature anomalies, with below average temperatures in western Canada and above average temperatures across the southern half of the United States (Fig. E1). They were also associated with increased precipitation in the northwestern and Gulf Coast regions of the U.S. (Figs. E3, E6).

c. Eurasia

The circulation during March featured a split-flow pattern over the eastern North Atlantic , a strong trough over eastern Europe/ Black Sea , and an anomalous ridge east of the Caspian Sea (Fig. E9). This pattern was associated with increased storminess and above average precipitation in eastern Europe, and with well above average temperatures across central Asia .

  2. Southern Hemisphere

    The circulation during March continued to exhibit a strong connection to La Niña, with an enhanced ridge over the central South Pacific and an anomalous trough over the high latitudes of the eastern South Pacific (Figs. E15, T22).

    In southern Africa , the rainy season extends from October through April. Rainfall during March was above-average for the region as a whole (Fig. E4), with surpluses mainly in the central and eastern portions of southern Africa (Fig. E3). Overall, the 2008-09 rainy season has been above average, which is consistent with La Niña.