The circulation during June featured above-average heights across the east-central North Pacific and the western United States, over the northeastern United States, over the eastern North Atlantic and Europe, and across central Russia (Fig. E9). The circulation also featured below-average heights over central Canada, the polar region and the higher latitudes of the North Atlantic. In the subtropics and lower mid-latitudes, there remains considerable symmetry of the upper-level circulation anomalies in both hemispheres (Fig. T22, bottom). During June, this pattern was dominated by anticyclonic circulation anomalies extending across both hemispheres in the 20°-50° latitude band.

Since mid-1998 the most notable aspects of this pattern have been anticyclonic anomalies extending eastward in the Northern Hemisphere from the Atlantic Ocean to Asia and in the Southern Hemisphere from the Atlantic Ocean eastward to Australia. This pattern is consistent with ongoing La Niña conditions, and is the leading mode of atmospheric variability on both the interannual and interdecadel time scales.

a. North America

Above-average heights covered both the western and northeastern United States during June, and below-average heights extended northeastward from the northern Plains states to northeastern Canada (Fig. E9). This anomaly pattern was accompanied by enhanced northwesterly flow into the northern and central Plains states, which contributed to abnormally cool temperatures throughout the region (Fig. E1), as well as across central Canada. In contrast, temperatures in the southwest remained above-average (1°-2°C) during the month, in association with the positive height anomalies to the north.

The anomalous circulation during June also contributed to enhanced precipitation over central Canada, the Great Lakes, the Midwest, and the Southwest (Fig. E3, bottom). In the United States each of these areas had previously recorded significantly below-average precipitation totals during the past year. For example, the Midwest and Great Plains regions recorded their first month of substantially above-average rainfall since June 1999. The Southwest region recorded its first month of above-average rains since July 1999. The Great Lakes region recorded its second consecutive month of above-average rains, following a 9-month stretch of significantly below-average precipitation that began in August 1999 (Fig. E5).

Elsewhere, the southeastern region of the United States has recorded generally below-average rainfall since November 1999, with area-average totals below the 10^th percentile occurring during November 1999, February 2000 and May 2000 (Fig. E5). Farther south, near-average rains were reported in the Gulf Coast region during June. However, considerable dryness has persisted throughout this area since November 1999, with area-average totals often below the 10^th percentile during this 8-month period (Fig. E5).

B. Europe/ Asia

Most of Europe again experienced milder-than-average temperatures during June (Fig. E1), with mean temperatures exceeding the 90^th percentile across southern and central Europe. This warmth was associated with a continuation of above-normal heights across the region (Fig. E9), a feature which also contributed to below-average rainfall in central and eastern Europe during the month (Fig. E3).

2. Southern Hemisphere

The Southern Hemisphere circulation during June (Fig. E15) featured above-average heights over the middle latitudes of both the central South Pacific and western South Atlantic, and in the region southeast of Africa, and below-normal heights over the high latitudes of the eastern South Pacific and over the region south of Australia. Much of the central latitudes have experienced above-average heights for more than a year, in association with an extremely persistent pattern of anticyclonic circulation anomalies in both hemispheres extending from the Atlantic ocean eastward to Australasia (See Northern Hemisphere Highlights above).