Extratropical Highlights –October 2022

 

1. Northern Hemisphere

During the month of October, major teleconnection indices were primarily near-normal while SST anomalies across the tropical Pacific remained below normal and signaling La Nina conditions (Figs. E7, T18). The 500-hPa circulation during October featured primarily above-average heights for much of the Northern Hemisphere with the strongest departures from normal occurring in the North Pacific Ocean and a wave-train feature across the North Atlantic Ocean (Fig. E9).  The main land-surface temperature signals include above-average temperatures for western North America, eastern Europe, and Russia (Fig. E1). The main precipitation signals include below-average totals in eastern and western regions of North America and around the Mediterranean Sea, and above-average totals in Russia (Fig. E3).

 

a. North America

The 500-hPa circulation during October featured above-average heights along the western and eastern coasts of North America and a slight tilt toward below-average heights over the Ohio Valley (Fig. E9). This pattern contributed to above-average temperatures for western Canada and Alaska, as well as across central Canada and toward the east (Fig. E1). With the exception of the West Coast, much of the U.S. recorded near-normal temperature conditions for the month of October (Fig. E1). The amplified ridge pattern led to widespread below-average rainfall for the Great Plains and most of the West Coast states, as well across the Southeast and Ohio Valley (Fig. E6). Precipitation totals were above normal for the Southwest and Northern Rocky states like Montana, where some of these areas recorded rainfall in the 60th percentile and greater (Figs. E3, E6).

 

b. Europe and Russia

A wave-train feature was predominant across the North Atlantic Ocean ending with an amplified ridge over Europe (Fig. E9). Across Russia the 500-hPa circulation was predominantly near-normal except for Northern Russia where moderate above-average heights were recorded over western Siberia and moderate below-average heights were recorded over eastern Siberia. The main temperature signals include large departures from normal for most of Europe and Russia where some areas recorded temperatures in the 90th percentile of occurrences (Fig. E1). The main precipitation signals were areas of above-average rainfall near the Kara Sea and for the area between the Kamchatka Peninsula and Chukchi Mountains, and below-average rainfall across the Mediterranean countries (Fig. E3).

 

b. West African monsoon

The west African monsoon season extends from June through October, with a peak during July-September. During 2022, the west African monsoon system was enhanced as early as March and continued thru October (see Sahel region, Fig. E4), with area-average rainfall totals reaching the 100^th percentile of occurrences in the Spring, and again in September, before reducing to the 60th percentile for October.

 

2. Southern Hemisphere

The 500-hPa height field during October featured an anomalous wave pattern across the South Pacific Ocean with a maxima of above-average heights between Australia and Antarctica, and a minima over the Bellingshausen Sea (Fig. E15).  The South African monsoon season runs from October to April. During October 2022, this area recorded below-average precipitation, with many locations recording totals in the lowest 10^th percentile of occurrences (Fig. E4).  The main precipitation signals include above-average rainfall in eastern Australia where rainfall was recorded in the 90th percentile of occurrences, and below-average rainfall for southern Africa which reached the lowest 10th percentile of occurrences (Fig. E3).

The Antarctic ozone hole typically develops during August and reaches peak size in September. The ozone hole then gradually decreases during October and November, and dissipates on average in early December (Fig. S8). By the end of October 2022, the size of the ozone hole was just over 20 million square kilometers, which is well above the 2012-2021 average size of 12 million square kilometers.

Polar stratospheric clouds (PSCs) were near zero and near-normal (Fig. S8) while the vortex area remained above average (Fig. S8). This highly anomalous ozone hole and vortex is not associated with a sudden stratospheric warming (Fig. S4, see September thru October).  The 50-hPa height anomalies show well-below average heights over Antarctica (Fig. S1).