After a prolonged spell of cool conditions across much of Europe, a dramatic swing in temperatures is expected in the coming days as warmer air surges north into western and central parts of the continent.
A large blocking high over the North Atlantic and slow-moving low pressure across southern Scandinavia dragged Arctic air southwards last week, sending temperatures 10-15C below the seasonal average for more than a week.
Overnight frosts affected gardeners and farmers, including in France, where grape growers lit fires to protect vineyards. Such widespread and persistent cold weather has become increasingly rare in recent decades as Europe continues to warm faster than any other continent as a result of the climate crisis.
The cool, unstable air also combined with strong May sunshine to trigger widespread thunderstorms. Between 11 and 16 May, about 750,000 lightning strikes were recorded across Europe and the surrounding areas.
Serbia’s national weather and hydrological service issued red warnings for strong winds, heavy rainfall and hail. Over the weekend, an extension of low pressure farther to the north-west of Europe cut off the northerly flow and winds turned more westerly.
Later this week, a large area of high pressure is forecast to build across western parts of the continent, drawing in hot air from north Africa. By Friday, temperatures in countries including France and England could climb 15C higher than a week earlier, reaching the mid- to high-30s celsius in Spain and Portugal. Overnight lows in these regions may exceed daytime highs recorded last week.
Dramatic temperature contrasts are also unfolding across the US this week. In late spring, such swings can be especially pronounced. In the north-west, where temperatures soared to about 30C last week, cold air is sweeping south from Canada and interacting with low pressure to produce the region’s second winter storm of the month.
Significant snowfall is forecast across higher terrain in Wyoming, northern Colorado and north-east Utah early this week, with up to 46cm (18in) possible over the highest ground. Winds of up to 60mph (96km/h) are expected to whip up blizzards and create hazardous driving conditions in places.
Farther south-west, gusty winds and persistently low humidity have triggered red-flag warnings across several states, signalling a heightened risk of wildfires.
To the east, the sharp contrast between the cold air and warmer, more humid conditions across the central US is likely to fuel further thunderstorm development.
The Storm Prediction Center has warned of a 15% tornado probability for Monday across four central states, spanning a region home to almost 900,000 people.