Extratropical Highlights – June 2014

 

1. Northern Hemisphere

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

 

a. North Pacific/ North America

The mean 500-hPa circulation during June featured above-average heights across the high latitudes of the North Pacific and eastern Canada, and below-average heights extending southward from Alaska to the western U.S. (Fig. E9). Over North America, this anomaly pattern was associated with an amplified trough in the west, and a disappearance of the mean Hudson Bay trough. These conditions contributed to well above-average precipitation extending from central Canada to the U.S. Gulf Coast (Fig. E3), with the central U.S. and central Canada both recording totals in the upper 90^th percentile of occurrences.

Much of the U.S. northern and central Plains states recorded 175% or more of their normal rainfall for June (Fig. E6). This marks the first month since November 2013 that the Great Plains recorded above-average precipitation (Fig. E5). For the Midwest Region, June marks only the second month of well above-average precipitation since June 2013.

According to the U.S. Drought Monitor (http://droughtmonitor.unl.edu), this above-average precipitation helped to lessen drought conditions in the Midwest and central Plains states. The most significant improvements occurred in Nebraska, Kansas, and Oklahoma, where only small regions of extreme drought persisted at the end of the month. However, exceptional drought persisted in portions of northern Texas. Exceptional drought also continued in central California and northwestern Nevada, and severe or extreme drought extended across the U.S. Southwest, California, southern Oregon, central Washington, and southern Idaho.

 

2. Southern Hemisphere

The mean 500-hPa circulation during June featured above average heights over the central ocean basins, and below-average heights over the high latitudes of the South Pacific and south of Africa (Fig. E15). In southeastern Australia, exceptionally warm and dry conditions continued during the month. Temperature departures were generally within the upper 70^th percentile of occurrences, and precipitation deficits were in the lowest 30^th percentile of occurrences (Figs. E3, E4). Conversely, northeastern Australia recorded above-average precipitation during the month, which follows an extended period of below-average precipitation dating back to last June.