Extratropical Highlights –August 2016

 

1. Northern Hemisphere

The 500-hPa circulation during August featured above-average heights over the high latitudes of both the western and eastern North Pacific, the northeastern U.S., Europe, and western Russia, and below-average heights over the central North Atlantic and the polar region (Fig. E9). This overall pattern projected strongly onto several teleconnection patterns, including the positive phase of the East Atlantic (+2.1) and Polar/Eurasia (+2.4) patterns and the negative phase of the North Atlantic Oscillation (NAO, -2.2) and East Atlantic/ West Russia (-3.3) pattern (Table E1, Fig. E7).

The main land-surface temperature signals during August included above-average temperatures in Alaska, western Canada, the eastern U.S., Europe, western Russia, and China (Fig. E1). The main precipitation signals included above-average totals in the southern and central U.S., and below-average totals in the Pacific Northwest and northeastern U.S. (Fig. E3).

 

a. North America

The 500-hPa circulation during August featured above-average heights over the Gulf of Alaska and the northeastern U.S., along with a broad trough across central North America (Fig. E9). This pattern was associated with above-average surface temperature in Alaska, western Canada, and the eastern U.S. (Fig. E1), with departures exceeding the 90^th percentile of occurrences in both southwestern Alaska and the eastern U.S.

Precipitation during August was above average across the southeastern and central U.S. (Fig. E3), with area-average totals exceeding the upper 90^th percentile of occurrences in the Great Plains, Midwest, and Gulf Coast regions (Fig. E5). Precipitation was below average in the Pacific Northwest and northeastern U.S., with monthly totals in both areas falling into the lowest 10^th percentile of occurrences.

According to the U.S. Drought Monitor, exceptional or extreme drought continued across central and southern California during August. Extreme drought also persisted in portions of northern Georgia and northeastern Wyoming, and developed in western New York and portions of New England. Severe drought was evident in eastern Oregon, western Nevada, and northern Mississippi. Moderate drought was evident in eastern Oregon, the southern half of New Mexico, and western Arizona.

 

b. Europe/ western Russia

The 500-hPa circulation during August featured above-average heights over Europe and western Russia, and below-average heights over the central North Atlantic and the polar region (Fig. E9). This pattern projected strongly onto several teleconnection patterns, including the positive phase of the East Atlantic (+2.1) and Polar/Eurasia (+2.4) patterns and the negative phase of the North Atlantic Oscillation (NAO, -2.2) and East Atlantic/ West Russia (-3.3) pattern (Table E1, Fig. E7).

This overall pattern was associated with a continuation of above-average surface temperatures across Europe and western Russia, with the most significant departures exceeding the 90^th percentile of occurrences in western Russia (Fig. E1). Western Europe also recorded below-average precipitation during August, with totals in some locations falling into the lowest 10^th percentile of occurrences.

 

 

c. Northern Africa

The West African monsoon season, which lasts from June-September, has been well above average so far this year (Fig. E3). Area-averaged totals were above average during June, July, and August, with the June and July totals nearing the 100^th percentile of occurrences (Fig. E4).

 

2. Southern Hemisphere

The mean 500-hPa circulation during August featured above-average heights over Antarctica and south of Australia, and below-average heights over the high latitudes of the South Pacific and the central South Atlantic Ocean (Fig. E15). Surface temperature signals during August included above-average temperatures in southern South America and South Africa (Fig. E1).

 

The Antarctic ozone hole typically develop rapidly during August and reaches its peak size in September. The ozone hole then gradually decreases during October and November, and dissipates in early December (Fig. S8). During August 2016, the ozone hole intensified and reached 15 million square kilometers by the end of the month. This size is roughly the average for the 2006-2015 period.