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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
 
Extratropical Highlights - June 2006
 

1. Northern Hemisphere

The 500-hPa circulation pattern during June featured a persistent positive height anomalies in the middle latitudes, and negative anomalies in the polar region (Figs. E9, E11). The main centers of positive height anomalies were observed over western North America , the high latitudes of the North Atlantic , northern Europe , and Siberia , and coincided with areas of significantly above-average surface temperatures (Fig. E1). The main precipitation departures during June included well above-average totals in the Mid-Atlantic and northeastern U.S. , and below-average totals in the central U.S. and both central and northern Europe (Figs. E3, E5, E6).

            a. North America

Over North America , an anomalous upper-level ridge-trough pattern, characterized by above-average heights in the west and an amplified trough over the eastern U.S. , was evident during much of June. This pattern contributed to exceptionally warm surface temperatures in the western U.S. and much of Canada (Fig, E1). It also contributed to a large area of below-average precipitation in the area between the ridge and trough axes, with area-averaged totals across the central U.S. generally in the lowest 30th percentile of occurrences. In contrast, precipitation was significantly above-average downstream of the mean trough axis, with area-averaged totals in the Mid-Atlantic and northeastern regions of the U.S. exceeding the 90th percentile of occurrences (Fig. E5). In the Northeast, periods of exceptionally heavy rainfall resulted in severe flooding during the month.  Elsewhere, the Gulf Coast region of the U.S. recorded ongoing precipitation deficits during June, and has recorded below-average precipitation in every month since September 2005.

b. North Atlantic / Eurasia

      The 500-hPa circulation pattern during June featured persistent above-average heights across the high latitudes of the North Atlantic , northern Europe , and Siberia (Fig. E9). This pattern was associated with above-average temperatures across Eurasia , with mean departures exceeding 2C over large parts of Europe and 3C over central Russia . It was also associated with below average precipitation over much of Europe , with many areas recording totals in the lowest 10th percentile of occurrences. In southern Europe precipitation has been below-average since April 2006.

2. Southern Hemisphere

 

      The mean 500-hPa circulation pattern during June featured persistent above-average heights south of Australia and South America , and across the subtropical South Pacific, and below-average heights north of New Zealand , over the eastern South Pacific, and over the southern Indian Ocean (Fig. E15). Regionally, central South America recorded well above-average temperatures in association with an anomalous low-level flow of tropical origin from the Amazon Basin (Figs. E3, T20). In Australia the persistent anomalous anticyclonic circulation south of the continent was associated with extensive onshore flow at low levels from the south and east, and with anomalous descending motion across the south. This combination of conditions led to anomalously cool temperatures across the continent, and to well below-average precipitation across the southeast and west where totals were in the lowest 10th percentile of occurrences. Similar conditions also contributed to anomalously cool and dry conditions over much the continent during May.

 

 


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