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

1. Northern Hemisphere

The 500-hPa circulation during June 2003 featured positive height anomalies over the high latitudes of the North Pacific, Europe, and central Russia, and negative height anomalies over the central United States, the eastern North Atlantic, and western Russia (Fig. E10). The prominent temperature anomalies during the month included warmer-than-average conditions over the western United States, Europe, and central Russia, and cooler-than-average conditions across the eastern two-thirds of the United States and western Russia (Fig. E1). Prominent precipitation anomalies during the month included above-average totals in the southeastern and eastern United States, and below-average totals in Europe (Fig. E3).

a. Pacific/North America

The mean upper-level circulation during June featured above-average heights over the western and eastern North Pacific, and a broad trough over the central United States. This anomaly pattern occurred primarily during the first half of the month (Fig. A2.1). During the second half of June the positions of the mean upper-level ridge and trough over the U.S were reversed, with the trough axis aligned along the west coast and the ridge axis located over the central part of the country. For the month as a whole these circulation patterns contributed to above-average surface temperatures in the western U.S. (+1 to +2C) and to below-average temperatures (-1 to -2C) over most of the country east of the Rocky Mountains (Fig. E1).

Well above-average rainfall occurred across the southeastern and eastern United States during June, with totals exceeding the 90th percentile in the Gulf Coast, Southeast, Mid-Atlantic, and Ohio Valley regions (Figs. E3, E5). The Southeast, Ohio Valley, and Mid-Atlantic regions have recorded above-average precipitation in eight of the last nine months beginning September 2002. The Inter-Mountain region also recorded above-average precipitation during June. This area as a whole has received above-average precipitation in four of the last five months, which follows nearly two years of considerably below-average precipitation for the region. The only region of significantly below-average precipitation during June occurred in the Pacific Northwest, where totals were below the 10th percentile of occurrences. This dryness was related to an area of mean upper-level convergence (Fig. T23) located immediately downstream of the anomalous ridge axis (Fig. E12 right), and to an associated northward shift of the mean storm track into Canada (Fig. E14).

b. Europe/Russia

The upper-level circulation during June featured a persistent anomalous wave pattern of 500-hPa height anomalies extending from the eastern North Atlantic to central Russia (Fig. E12). This pattern was associated with deep troughs over the eastern Atlantic and western Russia, and ridges over Europe and central Russia (Fig. E10). This circulation contributed to warmer and drier-than-average conditions over much of Europe, with monthly mean temperatures exceeding the 90th percentile (Fig. E1) and rainfall totals dropping below the 10th percentile over much of the continent (Fig. E3). It also contributed to cooler and wetter-than-average conditions across western Russia, with mean temperatures below the 30th percentile and rainfall totals in some areas exceeding the 90th percentile.

2. Southern Hemisphere

In the Southern Hemisphere the 500-hPa circulation during June featured above-average heights over Antarctica, the central South Pacific, the high latitudes of the Indian Ocean, and southern South America, and below-average heights over the eastern South Pacific, the central Indian Ocean, and in the area south of Australia (Fig. E16). The circulation anomalies across the polar region, the South Pacific, and South America were quite persistent and were evident on more than 80% of the days during the month (Figs. E16, E18).

Most of extratropical South America experienced well above-average temperatures during June, with monthly mean values exceeding the 90th percentile in much of the region (Fig. E1). Eastern Australia experienced above-average temperatures and a continuation of below-average rainfall during June. These conditions were related to the combination of an anomalous anticyclonic circulation at upper-levels (Figs. T21, T22) and anomalous dry westerly winds at low levels (Fig. T20).



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