Extratropical Highlights –April 2019

 

1. Northern Hemisphere

The 500-hPa circulation during April featured above-average heights over the western and eastern U.S., and Scandinavia, and below-average heights over the central North Pacific and the high latitudes of the North Atlantic (Fig. E9).

The main land-surface temperature signals included above-average temperatures in Alaska, much of the continental U.S., and Europe (Fig. E1). The main precipitation signals included above-average totals in the northwestern, central, and northeastern U.S., and portions of southern Europe, and below-average totals in northern Europe and Scandinavia (Fig. E3).

 

a. North America

The 500-hPa circulation during April featured above-average heights over the western and eastern U.S., along with a broad trough over the central U.S. (Fig. E9). This circulation contributed to above-average surface temperatures across Alaska much of the continental U.S. (Fig. E1). It also contributed to above-average precipitation in the northwestern, central, and northeastern U.S. (Fig. E3). According to the U.S. Drought Monitor, the continued restoration of soil moisture levels in the western U.S. has eliminated the extensive, extreme drought that had plagued much of the region during the past year.

 

b. Europe and Scandinavia

The 500-hPa height pattern during April featured a high-amplitude blocking ridge over Scandinavia (Fig. E9). This pattern resulted in a continuation of above-average surface temperatures throughout Europe (Fig. E1), along with below-average precipitation in northern Europe and Scandinavia (Fig. E3).

 

2. Southern Hemisphere

The 500-hPa height field during April featured above-average heights over the southern half of Australia and the central South Pacific Ocean (Fig. E15). In southern Africa, the monsoon season runs from October to April. During April, rainfall was above average for the region as a whole (Fig. E3). This makes April the only month in the 2018-19 monsoon season in which precipitation was appreciably above average (Fig. E4).