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

JUNE 2010

1. Northern Hemisphere

The 500-hPa height anomaly pattern featured considerable zonal symmetry during June, with above-average heights prevailing in both the middle latitudes and the polar region (Fig. E9). Regional anomalies included above average heights across the southeastern quadrant of the United States, Greenland, much of the Arctic Ocean, and across northern Europe and south-central Russia. Above average heights were also evident over the subtropical North Pacific and North Atlantic Oceans. Conversely, negative height anomalies prevailed over eastern Canada and central Siberia.

Over Eurasia, the circulation reflected a strong positive phase (+2.1) of the Polar/ Eurasia teleconnection pattern. Over the North Atlantic, the circulation again projected onto the negative phase of the North Atlantic Oscillation (NAO) (Table E1, Fig. E7). The negative NAO signal has been exceptionally persistent since July 2009.

Over the subtropical Atlantic basin, the 200-hPa streamfunction pattern showed a pronounced inter-hemispheric symmetry during June, with anticyclonic anomalies extending from the America’s to Africa in both hemispheres (Fig. T22). This signal is consistent with an enhanced west African monsoon circulation (Figs. T23, T24).

The main surface temperature signals during June included above average temperatures across the southeastern quadrant of the U.S., south-central Russia, and Mongolia (Fig. E1). The main precipitation signals included above-average totals in the northwestern and north-central U.S., portions of southern Europe, and southeastern China, and below average totals in the mid-Atlantic region of the U.S., south-central Russia, and Mongolia (Fig. E3).

a. North Pacific/ North America

Over the United States, the circulation during June featured a trough in the west and a ridge in the southeast (Fig. E9). This pattern was associated with above average temperatures throughout the southeastern quadrant of the country, with departures in many locations exceeding the 90^th percentile of occurrences (Fig. E1). It was also associated with enhanced storminess and above average precipitation in the Pacific Northwest, northern Plains, upper Midwest, and Great Lakes regions (Figs. E3, E5, E6). Many of these locations recorded more than double the normal June rainfall, with monthly totals in the upper 90^th percentile of occurrences. In contrast, the mid-Atlantic region experienced ongoing precipitation deficits during June, following well below average precipitation during both April and May (Fig. E5).

b. North Atlantic

The 500-hPa circulation during June featured above average heights across the central North Atlantic, and below average heights over the northwestern Atlantic (Fig. E9).  This pattern projected onto the negative phase of the NAO, which has persisted since July 2009 (Fig. E7).

Over the subtropical Atlantic, anticyclonic streamfunction anomalies at 200-hPa extended from the America’s to Africa in both hemispheres (Fig. T22). This pronounced inter-hemispheric symmetry to the anomaly pattern was associated with an expanded area of upper-level easterly wind anomalies that extended across tropical northern Africa and the tropical North Atlantic (Fig. T21). It was also associated with an extensive area of low-level westerly wind anomalies across the tropical Atlantic (Fig. T20). These conditions lead to reduced vertical wind shear across the tropical Atlantic, and are typical of the ongoing high activity era for Atlantic hurricanes that began in 1995. This combination of conditions is consistent with an enhanced west African monsoon circulation (Figs. T23, T24), which was also present during June and has been a prominent feature of the circulation since 1995.

c. Eurasia

The 500-hPa circulation during June featured a north-south dipole pattern of height anomalies, with above average heights extending from northern Europe to Mongolia, and below average heights over central Siberia (Fig. E9).  This pattern reflected a strong positive phase (+2.1) of the Polar/ Eurasia teleconnection pattern (Fig. E7). It was associated with exceptionally warm and dry conditions in south-central Russia, northeastern China, and Mongolia. The most significant departures were observed in the vicinity of the Black Sea and Caspian Sea, where temperatures (Fig. E1) were in the upper 90^th percentile of occurrences and precipitation was in the lowest 10^th percentile of occurrences.

At 200-hPa cyclonic streamfunction anomalies during June extended from northern India to eastern China, in association with a reduced strength and westward retraction of the normal summertime Asian monsoon ridge (Fig. T22). These conditions contributed to above average precipitation in southeastern China (Fig. E3). For China as a whole, precipitation has been above normal for the past three months (Fig. E4).

 2. Southern Hemisphere

The 500-hPa circulation during June featured a zonally symmetric pattern of height anomalies, with above average heights in the middle latitudes and below average heights over Antarctica (Fig. E15). The main precipitation anomalies were observed in eastern and southwestern Australia, where totals were generally in the lowest 30^th percentile of occurrences (Fig. E3). The main temperature signals reflected warmer than average conditions in both central Argentina and portions of western Australia (Fig. E1).