Extratropical Highlights –June 2020

 

1. Northern Hemisphere

The 500-hPa circulation during June featured above-average heights over the eastern North Pacific Ocean, central Canada, Europe, the central North Atlantic, and Scandinavia (Fig. E9). Below-average heights were observed over southern Alaska and western Europe.

The main land-surface temperature signals during June included above-average temperatures in the north-central U.S., Scandinavia, western Russia, eastern China, and central Siberia (Fig. E1). The main precipitation signals included above-average totals in the northwestern, south-eastern and Gulf Coast regions of the U.S., eastern Europe, and China, and below-average totals in the south-central U.S. and eastern Canada (Fig. E3).

 

a. North America

The 500-hPa circulation during June featured above-average heights over the eastern North Pacific Ocean and central Canada, and below-average heights over southern Alaska (Fig. E9). These anomalies were associated with an overall amplified wave pattern across North America, including enhanced jet stream winds over the northwestern U.S. (Fig. E10).

These conditions contributed to exceptionally warm surface temperatures in the north-central U.S., with large areas recording departures in the upper 90^th percentile of occurrences (Fig. E1). They also contributed to above-average precipitation in the northwestern, southeastern and Gulf Coast regions of the U.S. (Fig. E3).

 

b. Eurasia

The 500-hPa circulation during June featured a split flow pattern coming into Europe, in association with above-average heights over Scandinavia and below-average heights over western Europe (Fig. E9). This pattern contributed to above-average temperatures in Scandinavia and western Russia (Fig. E1), and to above-average precipitation in eastern Europe (Fig. E3).

Over eastern Siberia, a highly amplified ridge at 500-hPa (Fig. E9) was associated with anomalous southwesterly flow that extended into the polar region. This pattern contributed to well above-average surface temperatures throughout the region, with many areas recording departures in the upper 90^th percentile of occurrences (Fig. E1).

Over the eastern half of China, exceptionally warm (Fig. E1) and wet (Fig. E3) conditions were observed during June. These conditions were associated with anomalous upper-level divergence (Fig. T23) situated downstream of the mean 500-hPa trough (Fig. E9), and with anomalous southwesterly winds at 850-hPa (Fig. T20), both of which reflected an enhanced Southeast-Asian monsoon.

 

2. Southern Hemisphere

The 500-hPa height field during June featured above-average heights over Australia, New Zealand, and the high latitudes of the South Atlantic (Fig. E15). Below-average heights were observed over the high latitudes of the eastern South Pacific Ocean. This overall pattern contributed to anomalously dry conditions in both western and eastern Australia (Fig. E3).