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

1. Northern Hemisphere

The 500-hPa circulation during November 2003 featured above-average heights across the North Pacific, over the southeastern U.S., and over Scandinavia/ eastern Europe, and below-average heights over western North America, the high latitudes of the North Atlantic, and central Russia (Figs. E10, E12). These anomalies were associated with significant changes in the mid-latitude jet streams, including a westward retraction of the East Asian jet core to well west of the date line, and the development of a strong jet stream across the north-central United States (Fig. T21).

Above-average surface temperatures were observed in the eastern U.S., and most of Alaska and Europe during November (Fig. E1), while below-average temperatures were observed in the western United States and portions of central Siberia. Prominent precipitation anomalies during the month included below-average totals along the eastern seaboard of the United States, the eastern Mediterranean Sea, and eastern Europe (Fig. E3).

a. Pacific/North America

The mean upper-level circulation during November featured a broad ridge south of the Aleutian Islands and a trough across North America (Fig. E10). This represents a significant westward shift of the mean ridge and trough axes from their climatological mean locations over western and eastern North America, respectively. This circulation was associated with a three-celled pattern of height anomalies, with positive anomalies over the high latitudes of the North Pacific and the southeastern U.S., and negative anomalies over western North America. This anomaly pattern reflected a strong negative phase (-1.8) of the Pacific/ North American (PNA) teleconnection pattern (Table E1, Figs. E7, E8).

The negative PNA pattern during November was also associated with a pronounced westward retraction of the East Asian jet core to well west of the date line (Fig. T21), and with a northward shift of the mean westerlies to Alaska. This circulation contributed to above-average temperatures in Alaska.

A well-defined jet stream was also evident across the north-central and northeastern United States (Fig. E11). The pronounced westward shift of this jet stream, which is normally located over the North Atlantic, is consistent with the westward shift of the mean upper-level ridge and trough axes during the month. This circulation contributed to below-average temperatures in the northwestern U.S. and to above-average temperatures in the eastern part of the country (Fig. E1). It also contributed to above-average precipitation in the Inter-Mountain and Great Lakes regions (Fig. E5), and to below-average precipitation in the Southeast, Mid-Atlantic, and Northeast regions. These latter areas were situated along the mean upper-level ridge axis and south of the mean jet core (Fig. T22).

b. Europe

A large-amplitude ridge extended southward from Scandinavia to the Mediterranean Sea during November, while upper-level troughs covered the high latitudes of the North Atlantic and central Russia (Fig. E10). This blocking pattern projected very strongly onto the positive phase (+1.9) of the Scandinavia teleconnection pattern (Table E1, Figs. E7, E8). Over the eastern North Atlantic this circulation was associated with a pronounced split flow configuration, with the northern branch of the jet stream entering the continent near Great Britain and the southern branch entering near southern Portugal (Fig. T21). This circulation was consistent with above-average temperatures over most of Europe (Fig. E1). Farther downstream the blocking pattern brought below-average temperatures to central Russia, and also contributed to below-average precipitation in areas such as eastern Europe and the eastern Mediterranean Sea, regions that were situated beneath the mean upper-level ridge axis.

2. Southern Hemisphere

In the Southern Hemisphere the 500-hPa circulation during November featured above-average heights south of Australia and over the high latitudes of the eastern North Pacific, and below-average heights over the Indian Ocean, the central South Pacific, and southern South America (Fig. E16). This overall circulation was associated with enhanced upper-level westerlies across the central South Pacific, and with warmer (Fig. E1) and wetter (Fig. E3) than average conditions over southern South America. Over Australia significantly above-average temperatures were observed in the southeast, and above-average precipitation was recorded in the south-central portion of the continent.

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