Extratropical Highlights –July 2023

 

1. Northern Hemisphere

The 500-hPa circulation during July featured above-average heights over much of North America, Greenland, the North Atlantic Ocean, the North Pacific Ocean, and the Mediterranean (Fig. E9). Below-average heights were observed across Europe, Scandinavia, over the Laptev Sea, and central Canada (Fig. E9). Of note, records indicate that globally speaking, July 2023 was the hottest month on record.  The main land-surface temperature signals include above-average temperatures for the western half of North America, Europe and Asia (Fig. E1). The main precipitation signals include above-average totals in eastern North America, United Kingdom, Scandinavia, and regions across Russia, and below-average rainfall totals across the southern U.S., Alaska Panhandle, and eastern Canada (Fig. E3).

 

a. North America

The 500-hPa anomaly pattern over North America featured strong ridging over northern Canada and Alaska, as well as weaker ridging over much of the western U.S., and weak troughing over central Canada (Fig. E9).  This pattern ushered in strongly above-average temperatures across the western and southern U.S., western Canada, and the interior of Alaska where much of these areas recorded temperatures in the 90th percentile of occurrences (Fig. E1).  The U.S. Southwest recorded 30 consecutive days where temperatures reached or exceeded 110F, breaking the previous record of an 18-day streak.  July featured a drier than average start for the Southwest Monsoon where departures from average were in the lowest 10th percentile of occurrences (Figs. E3, E5, E6).  Below-average rainfall was recorded across the Gulf Coast and North Plains while much of the Northeast and Mid-Atlantic Seaboard recorded above-average rainfall (Figs. E5, E6).  The Northeast in particular recorded rainfall in the highest 90th percentile of occurrences (Fig. E5).  According to the U.S. Drought Monitor, the Northwest and Southwest have recorded either no change or a Class 1 Degradation in drought status for the month of July.

 

b. Eurasia

Across the northern half of Eurasia, troughing was the main feature in the anomalous 500-hPa height pattern, with a maxima occurring over the North Sea and the Laptev Sea (Fig. E9). Across the rest of Eurasia, anomalous 500-hPa heights were either near-normal or weakly positive (Fig. E9). Despite the weak ridging pattern, much of Eurasia recorded significantly above-average temperatures with many areas exceeding the 90th percentile of occurrences (Fig. E1). Above-average rainfall was recorded across the United Kingdom, Scandinavia, and parts of central Russia (Fig. E3).  Above-average rainfall was also recorded across southern Asia (Fig. E3).  Many of these same locations recorded rainfall in the highest 90th percentile of occurrences (Figs. E3, E4).

 

2. Southern Hemisphere

The 500-hPa height field during July featured a mixed pattern of above- and below-average height anomalies across the Southern Hemisphere.  The main features were strongly above-average heights off the coast of Antarctica, centered near the Bellingshausen Sea, and strongly below-average heights off the coast of Antarctica in the southern Indian Ocean (Fig. E15).  Near the Tropic of Capricorn, ridging was featured over Australia, parts of southern Africa, and central South America (Fig. E15). Warmer than average temperatures were recorded for much of South America and eastern Australia with many areas reaching the highest 90th percentile of occurrences (Fig. E1). Drier than average conditions were observed across Argentina, Brazil, and the southern tier of Australia where many of these areas recorded rainfall in the lowest 10th percentile of occurrences (Fig. E3).