Extratropical Highlights –March 2020

 

1. Northern Hemisphere

The 500-hPa circulation during March featured above-average heights across the central North Pacific, the eastern half of the U.S., and in the vicinity of the Caspian Sea, and below-average heights across the polar region and the southwestern U.S. (Fig. E9).

The main land-surface temperature signals during March included above-average temperatures throughout the central and eastern U.S. and throughout Eurasia (Fig. E1). The main precipitation signals included above-average totals in the central U.S. and northwestern Russia, and below-average totals in the northwestern U.S. (Fig. E3).

 

a. North America

The 500-hPa circulation during March featured above-average heights over the central North Pacific and the eastern half of the U.S., and below-average heights in the southwestern U.S. (Fig. E9). This pattern was associated with highly anomalous jet stream patterns, including a westward retraction to Japan of the East Asian jet core, and a markedly enhanced subtropical jet stream across the southwestern and central U.S. (Fig. T21).

These conditions were associated with well above-average surface temperatures across the central and eastern U.S., with departures in many regions exceeding the 90^th percentile of occurrences (Fig. E3). They were also associated with above-average precipitation from the southwestern U.S. to the upper Midwest (Fig. E3). The most significant precipitation anomalies were observed in the Great Plains and Midwest regions, were area-averaged totals were in the upper 90^th percentile of occurrences (Fig. E5). Both of these regions have recorded well above-average precipitation for the past three months.

 

b. Eurasia

The 500-hPa circulation during March featured above-average heights across central Russia and below-average heights in the polar region (Fig. E9). This pattern was associated with a pronounced on-shore flow of milder marine air into northern Europe, and with a confinement of polar air to the very high latitudes. These conditions contributed to a continuation of exceptional warmth across Eurasia, with much of central and western Russia recording departures in the upper 90^th percentile of occurrences (Fig. E1). For northern Europe and much of Eurasia, this represents a continuation of exceptional warmth that has persisted for several months.

 

2. Southern Hemisphere

The 500-hPa height field during March featured above-average heights over the southern South Pacific and Indian Oceans, and across southern South America, and below-average heights in the polar region (Fig. E15). In southeastern Australia, well 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 2020, precipitation was below-average in the south and above-average in the north. For the monsoon region as a whole, area-averaged rainfall totals were below average (Fig. E4). Previously, area-averaged totals had been below average during the first five months of the 2019-2020 rainy season.