Extratropical Highlights –March 2021

 

1. Northern Hemisphere

The 500-hPa circulation during March featured highest above-average heights across the central North Pacific, with moderate above-average heights across the eastern half of the U.S., Gulf of Mexico region, and northern portions of the North Atlantic Ocean and below-average heights stretching from northern Canada into northern and central Russia (Fig. E9).

The main land-surface temperature signals during March included above-average temperatures throughout central and eastern portions of Canada and the U.S., southern Eurasia, as well as the central and eastern portions of Russia.  (Fig. E1). The main precipitation signals included above-average totals in the central regions of the U.S., the northern and western portions of Russia, and in the vicinity of Egypt and the western Sahara (Fig. E3).

 

a. North America

The 500-hPa circulation during March featured highest above-average heights across the central North Pacific, with moderate above-average heights across the central and eastern portions of the U.S. and Canada, the Gulf of Mexico and adjacent regions, and below-average heights across Alaska and adjacent portions of Canada.  (Fig. E9). This pattern was associated with an anomalous jet stream pattern across the North Pacific Ocean and enhanced subtropical jet stream across southwestern and central U.S. (Fig. T21).

These conditions were associated with well above-average surface temperatures across the central and eastern portions of Canada and the U.S., with departures in many regions exceeding the 90^th percentile of occurrences (Fig. E1). They were also associated with above-average precipitation from the Great Plains to the upper Midwest in the U.S.  (Fig. E3). In these regions, the most significant precipitation anomalies were observed with totals in the 90^th percentile of occurrences (Fig. E5).

 

b. Eurasia

The 500-hPa circulation during March featured moderate above-average heights across Iceland to western Europe, thru Saudi Arabia, India, China, and Japan, and the northeastern flanks of Eurasia, where the largest departures from normal are observed, and below-average heights stretching from northern Canada into northern and central Russia toward the vicinity of the Caspian and Black Seas.  Lowest below-average heights are near the East Siberian Sea and the northwestern region of Russia. (Fig. E9).  This pattern ushered in warmer conditions for the southern and eastern portions of Eurasia and enhanced storm tracks across a southwest to northeast tilt in central Eurasia (Figs. E1 and E3).

 

2. Southern Hemisphere

The 500-hPa height field during March featured moderate above-average heights across southern South America and the south Pacific Ocean with highest departures from normal over the Southern Ocean and adjacent portions of Antarctica.  Below-average heights in the southeastern portion of Australia, and the southern portions of the Atlantic Ocean, Indian Ocean, and Pacific Ocean, specifically near the Ross Sea where the largest departures from normal are located (Fig. E15). In southeastern Australia, above-average precipitation was recorded during March (Fig. E3). This increased rainfall resulted from increased storminess linked to enhanced upper-level westerlies (Fig. T21) and cyclonic streamfunction anomalies (Fig. T22) across the region.

The South African monsoon season runs from October to April. During March 2021, precipitation was below-average in the eastern half of southern Africa and above-average in the western half (Fig. E3).  For the monsoon region, area-averaged rainfall totals were below average for March 2021 (Fig. E4). In the preceding 3 months, area-averaged totals had been at the 80th percentile or above following a drier than average start to the 2020-2021 rainy season (Fig. E4).