Extratropical Highlights – February 2021

 

1. Northern Hemisphere

The 500-hPa circulation during February featured above-average heights across the central and eastern North Pacific, the Gulf of Alaska, the northwestern Atlantic, the northern pole region, and the mid-latitudes of Eurasia, and below-average heights over North America, the northeastern Atlantic, and the high-latitudes of Eurasia. (Fig. E9).

The main land-surface temperature signals during February included above-average temperatures over eastern Canada and mid-latitudes of Eurasia, and below-average temperatures across the western half of Canada, much of the U.S., and the high-latitudes of Eurasia (Fig. E1). The precipitation was above average in the Pacific northwest and the eastern U.S., and below average in the southwestern and central U.S., and eastern Canada (Figs. E3, E6).

 

a. North Pacific and America

The 500-hPa circulation during February was dominated by below-average heights over most of the U.S., and above-average heights over eastern Canada (Fig. E9). These anomalous circulations contributed to below-average surface temperatures in most of the U.S., with departures in the lower 10^th percentile of occurrences in the central U. S. (Fig. E1). Also, precipitation was above average in the Pacific northwest and the eastern U.S., and below average in the southwestern and central U. S. (Figs. E3, E5, E6). According to the U.S. Drought Monitor, dry conditions dominated much of the West and especially the Southwest and the Plains.

 

b. Eurasia

The 500-hPa height pattern featured above-average heights over the mid-latitudes of Eurasia and below-average heights over the high latitudes of Eurasia (Fig. E9). This pattern resulted in above-average surface temperatures throughout the mid-latitudes of Eurasia and below average over the high latitudes of Eurasia, with some areas recording departures in the upper 90^th percentile of occurrences (Fig. E1).

 

2. Southern Hemisphere

The mean 500-hPa circulation during February generally featured an overall increase of the meridional gradient with above-average heights in the middle latitudes and below-average heights over Antarctica (Fig. E15). Much of South America recorded above-average temperature and below-average precipitation during February (Figs. E1, E3), in association with the impact of La Niña (Figs. T18, T22, T25).

The South African monsoon season runs from October to April. During February, rainfall was above average for the region as a whole (Fig. E4). The most significant departures were observed in the southeastern portion of the monsoon region, with totals in the highest 70^th-90^th percentile of occurrences (Fig. E3). To date, the monsoon region has recorded above-average precipitation during November 2020- February 2021.