Extratropical Highlights – June 2012

 

1. Northern Hemisphere

The 500-hPa circulation during June featured above-average heights over the central U.S., the high latitudes of the North Atlantic, and north-central Russia, and below-average heights over the Gulf of Alaska, the central North Atlantic, and northern Europe (Figs. E9, E11). Over the North Atlantic, the circulation projected onto a strong negative phase (-2.2) of the North Atlantic Oscillation (NAO) (Fig. E7, Table E1).

The main land-surface temperature signals during June included well above-average temperatures across the central United States, southern Europe, and central Russia (Fig. E1). The main precipitation signals (Fig. E3)  included above-average totals in the northwestern U.S. and northern Europe, and below-average totals in the central U.S. (Fig. E6) and southern Europe.

 

a. North America

The mean 500-hPa circulation during June featured an amplified wave pattern across North America. Key features of this pattern included an enhanced ridge over the central U.S., and enhanced troughs over the Gulf of Alaska and the western North Atlantic. The surface temperature and precipitation anomalies were consistent with this pattern, and included exceptionally hot and dry conditions over the central U.S., and cooler and wetter than average conditions in the Pacific Northwest and western Canada (Figs. E1, E3).

In the U.S., extreme or exceptional drought was present by the end of June in portions of sixteen states, including those in the southwest, the southern Plains, the Tennessee Valley, and the southeast.

 

b. North Atlantic and Europe

The 500-hPa circulation during June featured a strong negative phase (-2.2) of the NAO (Fig. E7, Table E1), as indicated by persistent positive height anomalies over Greenland and persistent negative height anomalies across the central and eastern North Atlantic (Figs. E9, E11). This pattern was associated with above-average precipitation across northern Europe, where area-averaged totals exceeded the 90^th percentile of occurrences (Fig. E4). It was also associated with anomalously warm and dry conditions across southern Europe, where area-averaged totals were in the lowest 20^th percentile of occurrences.

 

2. Southern Hemisphere

In the extratropics, the mean 500-hPa circulation during June featured an anomalous zonal wave-3 pattern, with above-average heights located south of Australia, over the central South Pacific, and over the central South Atlantic, and below-average heights located south of South America, south of Africa, and extending from southeastern Australia to New Zealand (Fig. E15). In Australia, the main precipitation signals included above-average totals along the west and east coasts (Fig. E3). Also, surface temperatures were well below-average in northern Australia (Fig. E1).