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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
Extratropical Highlights - July 2003

1. Northern Hemisphere

During July 2003 positive 500-hPa height anomalies were observed from eastern Siberia to the western United States, over Scandinavia, and across the central North Atlantic to northern Africa, and negative height anomalies were found over the eastern United States and the eastern North Atlantic (Fig. E10). The prominent temperature anomalies during the month included a continuation of significantly warmer-than-average conditions over the western United States and Europe, and cooler-than-average conditions over the eastern United States and central Russia (Fig. E1). Prominent precipitation anomalies during July included above-average totals in the southeastern and eastern United States, and below-average totals in the Pacific Northwestern states, western Canada, and northern Europe (Fig. E3).

a. Pacific/North America

The mean upper-level circulation during July featured a persistent pattern of above-average heights extending from eastern Siberia to the Rocky Mountains (Fig. E12). Associated with this anomaly pattern the mean upper-level ridge axis in North America was situated over the Rocky Mountains and shifted approximately 20 degrees longitude west of its climatological mean position. This circulation was accompanied by an amplified upper-level trough over eastern North America (Figs. E10, T22).

The significant rainfall and temperature departures during July in North America were associated with this anomalous ridge-trough structure. Over western North America below-average rainfall (Fig. E3) and significantly above-average temperatures (Fig. E1) coincided with the mean upper-level ridge. In the United States below-average rainfall also extended eastward to the Great Plains in the region between the mean upper-level ridge and trough axes (Figs. E5, E6). Conversely, above-average rainfall was observed across the southeastern and eastern United States in the area downstream of the mean trough axis. The Southeast, Ohio Valley, and Mid-Atlantic regions have recorded above-average precipitation in nine of the last ten months beginning September 2002 (Fig. E5).

b. Europe

The upper-level circulation during July featured a blocking pattern over Scandinavia, and a pronounced split-flow configuration farther south across northern Europe and western Russia (Fig. E10). This circulation contributed to significantly above-average temperatures throughout Europe, Scandinavia, and western Russia, with monthly mean temperatures exceeding the 90th percentile in each region (Fig. E1).

2. Southern Hemisphere

In the Southern Hemisphere the 500-hPa circulation during July featured above-average heights across the central South Pacific and the high latitudes of the South Atlantic, and below-average heights over the high latitudes of the eastern South Pacific and the central Indian Ocean (Fig. E16). Eastern Australia experienced a continuation of above-average temperatures and below-average rainfall during July, in association with a persistent anomalous anticyclonic circulation at upper-levels (Figs. T21, T22).

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Page last modified: January 15, 2002
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