Extratropical Highlights –June 2015

 

1. Northern Hemisphere

The mean 500-hPa circulation during June featured above-average heights over the high latitudes of the North Pacific, the western U.S., central Europe, and western Russia, and below-average heights over Scandinavia and the Mediterranean Sea (Fig. E9).

The main land-surface temperature signals during June included above-average temperatures in the western and eastern U.S., western Canada, Europe, and central Siberia (Fig. E1). The main precipitation signals during June included above-average totals across much of the mid- western and eastern U.S., and below-average totals in the northwestern U.S., western Canada, eastern Europe and western Russia (Fig. E3).

 

a. North Pacific/ North America

At 500-hPa, the circulation during June featured above-average heights over the western U.S. and a broad trough over eastern North America (Fig. E9). This pattern contributed to exceptionally warm (Fig. E1) and dry (Fig. E3) conditions across the western U.S. and western Canada, with many locations recording temperature departures above the 90^th percentile of occurrences and precipitation totals in the lowest 10^th percentile of occurrences. (Fig. E3). According to the U.S. Drought Monitor, the exceptionally dry conditions in the Pacific Northwest U.S. (Fig. E5) contributed to extreme drought in southern Oregon and western Montana, and also to severe drought across much of northern Oregon, Idaho, and Washington.

Large portions of the central and eastern U.S., which were situated within and downstream of the mean trough axis, recorded anomalously warm and wet conditions during June. Area-averaged rainfall totals in the Midwest, Ohio Valley, Mid-Atlantic, and Northeast regions were all above the 80^th percentile of occurrences (Fig. E5), with many locations recording more than 175% of normal precipitation (Fig. E6).

 

b. Eurasia

The 500-hPa circulation featured above-average heights over central Europe, and below-average heights across over Scandinavia (Fig. E9). This pattern contributed above-average surface temperatures across Europe (Fig. E1), and to below-average precipitation in eastern Europe and western Russia (Fig. E3). It was also associated with a continuation of well above-average surface temperatures in central Siberia. This region has recorded warmer than average conditions for the past five months.

 

2. Southern Hemisphere

The mean 500-hPa circulation during June featured above-average heights in the middle latitudes and below-average heights at high latitudes (Fig. E15). At 200-hPa, anti-cyclonic streamfunction anomalies in the tropics and subtropics over the central South Pacific reflected El Niño (Fig. T22). The main surface temperature departures included well above-average temperatures across much of southern South America, and in both western and eastern Australia (Fig. E3).