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

JULY 2010

1. Northern Hemisphere

The 500-hPa height field during July featured above-average heights over the eastern United States, the Gulf of Alaska, northern Europe/ north-western Russia, and eastern Siberia, and below average heights over north-central Russia and the polar region (Fig. E9). Over the North Atlantic, the circulation again projected onto the negative phase of the North Atlantic Oscillation (NAO) and the positive phase of the East Atlantic teleconnection pattern (Table E1, Fig. E7). Both of these patterns have persisted since July 2009 (Fig. E7).

Over the subtropical Atlantic basin, the 200-hPa streamfunction pattern showed a pronounced inter-hemispheric symmetry during July, with anticyclonic anomalies extending from the America’s to Africa in both hemispheres (Fig. T22). Conversely, an anomalous trough was evident across most of the tropical western North Pacific. A similar anomaly pattern was evident in the Southern Hemisphere. These signals are consistent with the combined influences of La Niña and an enhanced west African monsoon system (Figs. T23, T24).

The main surface temperature signals during July included above average temperatures across the eastern half of the U.S., Europe, northwestern Russia, and most of China (Fig. E1). The main precipitation signals included above-average totals in the south-central and Midwestern U.S., and in northern China, and below average totals in the mid-Atlantic, Northeast, and Pacific Northwest regions of the U.S., and northwestern Russia (Fig. E3).

a. North America

The mean 500-hPa circulation during July featured a broad ridge across the United States (Fig. E9). This pattern was associated with above average temperatures across the eastern half of the country, with departures in many locations exceeding the 70^th percentile of occurrences (Fig. E1). The most significant surface temperature departures were observed in the mid-Atlantic and northeastern states, where values exceeded the 90^th percentile of occurrences. These regions were also drier than average during July (Fig. E3), with the mid-Atlantic recording its fourth consecutive month of below average precipitation (Fig. E5). Elsewhere, precipitation was above average from the central Gulf Coast to the Great Lakes.

b. North Atlantic

The 500-hPa circulation during July featured above average heights across the central North Atlantic, and below average heights over the northeastern North Atlantic (Fig. E9).  This pattern projected onto the negative phase of the North Atlantic Oscillation (NAO) and the positive phase of the East Atlantic teleconnection pattern (Table E1, Fig. E7), both of which have persisted since July 2009 (Fig. E7).

Over the subtropical Atlantic, anticyclonic streamfunction anomalies at 200-hPa extended from the America’s to Africa in both hemispheres (Fig. T22). This pronounced inter-hemispheric symmetry to the anomaly pattern was associated with an expanded area of upper-level easterly wind anomalies that extended across tropical northern Africa and the tropical North Atlantic (Fig. T21). It was also associated with an extensive area of low-level westerly wind anomalies across the tropical Atlantic (Fig. T20). These conditions lead to reduced vertical wind shear across the tropical Atlantic, and are typical of the high activity era for Atlantic hurricanes that began in 1995. This combination of conditions is consistent with an enhanced west African monsoon circulation, which was also present during July (Figs. T23, T24) and has been a prominent feature of the circulation since 1995.

c. Eurasia

 2. Southern Hemisphere

The 500-hPa circulation during July featured a zonally-symmetric pattern of height anomalies, with above average heights in the middle latitudes and below average heights over Antarctica (Fig. E15). In the subtropics, the upper-level streamfunction pattern reflected an anomalous trough across the western and central tropical South Pacific, and an anomalous ridge extending from the eastern subtropical South Pacific to southern Africa (Fig. T22). A similar anomaly pattern was evident in the Northern Hemisphere. These conditions likely reflect the influences of La Niña and an enhanced west African monsoon system.

The main temperature signals during July reflected well above average temperatures in eastern Australia, where monthly departures were generally in the upper 90^th percentile of occurrences (Fig. E1).