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Climate Diagnostics Bulletin
Climate Diagnostics Bulletin - Home Climate Diagnostics Bulletin - Tropics Climate Diagnostics Bulletin - Forecast

 

  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

MAY 2009

Forecast Forum

1. Northern Hemisphere

The 500-hPa height field during May 2009 featured positive anomalies over the high latitudes of the central North Pacific and from the western U.S. to southern Europe , and negative anomalies over eastern Canada , the high latitudes of the North Atlantic , and north-central Russia (Fig. E9). Over the Pacific Ocean the circulation continued to reflect a westward retraction of the East Asian jet stream in association with the lingering La Niņa signal (Fig. T21).

The main temperature signals during May included above average temperatures in the southwestern U.S. and southern Canada , and below average temperatures across Canada (Fig. E1). The main precipitation signals included above average totals in the southeastern quadrant of the U.S. , and below average totals in southern Europe (Fig. E3).

 

a. North Pacific/ North America

Lingering La Niņa signals included a stronger than average tough over the central subtropical North Pacific, and above average heights over the high latitudes of the central North Pacific (Figs. T22, E9). Associated with this pattern, the East Asian jet stream was again retracted westward toward the western Pacific (Fig. T21). Over North America , the circulation during May featured above average heights at 500-hPa over the southwestern and southeastern U.S. , and below average heights over central and eastern Canada . This pattern was associated with below average surface temperatures across much of Canada , with departures in central Canada dropping into the lowest 10th percentile of occurrences (Fig. E1). It was also associated with above average temperatures in the southwestern U.S. , with many areas recording values in the highest 90th percentile of occurrences.

These conditions were accompanied by an enhanced storm track and 500-hPa trough situated over the central United States . The trough axis delineated areas of below average precipitation to the west and above average precipitation to the south and east (Fig. E3). Area-averaged totals were significantly above average in the Midwest , Southeast, and Ohio Valley regions, where departures exceeded the 90th percentile of occurrences.

 

b. North Atlantic and Eurasia

The circulation during May featured a dipole pattern of 500-hPa height anomalies over the North Atlantic , with below average heights in the north and above average heights in the south (Fig. E9). This pattern was associated with a focused storm track across the central North Atlantic and central Europe . These conditions contributed to below average precipitation across southern Europe , where departures were generally in the lowest 30th percentile of occurrences.

 

 

 

 

 

  2. Southern Hemisphere

   

The circulation during May reflected a zonal wave-2 pattern of 500-hPa height anomalies in the middle and high latitudes, with above average heights over the central South Pacific and in the area south of Africa, and below average heights over the high latitudes of the eastern South Pacific and southern Indian Ocean (Fig. T22). The anomaly pattern over the extratropical South Pacific continued to reflect a lingering influence from La Niņa.

The main temperature departures during May were seen in central South America , where values were in the upper 70th percentile of occurrences (Fig. E1). The main precipitation anomalies reflected below average totals in southwestern and southeastern Australia . Monthly totals in portions of the southeast were in the lowest 10th percentile of occurrences.


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Page Last Modified: June 2009
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