Re-Amplifying Upper Ridge To Extend European Drought

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Discussion: In September the super dry pattern of the 2018 warm season across Europe continued. Less than 50% of normal rainfall was observed across much of Southeast Europe, France and parts of north/northeast Europe plus Portugal into Spain and Italy.

The culprit is the stubborn upper level high pressure ridge locked-into the upper air pattern across Europe since last spring (Fig. 1) and amplifying during summertime due to the feedback to the atmosphere of widening dry soils. The upper ridge is the downstream result of the winter 2017-18 polar vortex lingering across eastern Canada to Greenland into the spring/early summer causing a vast region of cooler than normal ocean water to generate south of Greenland, east of the Canadian Maritimes and eastward toward Spain (Fig. 2).

The cool pool of water south of Greenland (and attendant cooler atmosphere above) maintained the mean upper trough through most of summer. Downstream from the lingering polar vortex the super ridge pattern evolved, anchored and strengthened over Europe causing the great drought of 2018.

What will it take to change this pattern? The cool ocean surface south of Greenland and the tendency for the polar vortex to be in that vicinity while downstream a warm/dry upper ridge causes European climate to stay dry and warm is not likely to change and likely worsens the next 2+ weeks (Fig. 3).

Fig. 1: The 500 MB anomaly pattern from May to September 2018 identifying a titanic upper ridge causing the summer drought.

Fig. 2: The Europe ridge was induced downstream from the polar vortex which lingered into summer 2018 across cooling SSTA south of Greenland.

Fig. 3: The ECM ENS (model) indicates the warm/dry upper ridge pattern of the warm season 2018 re-amplifies the next 2 weeks across Europe and Western Russia.