Extratropical Highlights – May 2014

 

1. Northern Hemisphere

The 500-hPa circulation during May featured above-average heights across the high latitudes of the North Pacific, northeastern Canada, and western Russia, and below-average heights over the central North Pacific, southeastern Europe, and the polar region (Fig. E9). The main land-surface temperature signals included well above-average temperatures along the west coast of North America, and western Russia (Fig. E1). The main precipitation signals included above-average totals along the U.S. Gulf Coast, Scandinavia, and eastern Europe, and below-average totals in southeastern Alaska, the southwestern and central U.S., southwestern Europe, and western Russia (Fig. E3).

 

a. North Pacific/ North America

The mean 500-hPa circulation during May featured a north-south dipole pattern of height anomalies across the North Pacific Ocean, with above-average heights at high latitudes and below-average heights in the lower extratropics (Fig. E9). Above-average heights were also present across Alaska and western North America (Fig. E9). This circulation contributed to warmer than average conditions across Alaska, and to warmer and drier than average conditions along the west coast of North America (Figs. E1, E3). Below-average precipitation was also recorded across the central U.S., while above-average rainfall occurred along the U.S. Gulf Coast and much of Texas (Fig. E3).

According to the U.S. Drought Monitor (http://droughtmonitor.unl.edu), precipitation deficits and drought continued across the U.S. central and southern Plains, with drought intensity ranging from severe – to – exceptional. Also during May, exceptional drought continued in central California and northwestern Nevada, and severe – to –extreme drought extended across the U.S. Southwest, California, and southern Oregon.

 

b. North Atlantic/ Eurasia

The mean 500-hPa circulation during May featured a broad trough over the high latitudes of the North Atlantic, and a sharp trough-ridge pattern extending across eastern Europe and western Russia (Fig. E9). This circulation was associated with exceptionally hot and dry conditions in western Russia in the vicinity of the Caspian Sea (Figs. E1, E3), and to above-average precipitation across Scandinavia and eastern Europe. Elsewhere an amplified ridge over the eastern North Atlantic contributed to below-average precipitation in southwestern Europe.

 

2. Southern Hemisphere

The mean 500-hPa circulation during May featured above-average heights over Antarctica and the central South Pacific, and below-average heights across the southern extratropics (Fig. E15). In eastern Australia, exceptionally warm and dry conditions were observed during the month. Temperature departures were generally within the upper 90^th percentile of occurrences, and precipitation deficits in some regions were in the lowest 10^th percentile of occurrences (Figs. E3, E4). Eastern Australia has recorded precipitation deficits in nearly every month since last May.