In parts of the south-east of the US, a line of severe thunderstorms occurred last weekend and generated a series of isolated tornadoes spanning eastwards from Texas through to northern Florida.
Days of heavy rain fed by the storms left soils saturated, triggering localised flash flooding. One particularly devastating tornado in a south-eastern Alabama town left at least four people dead on Monday, and further fatalities were reported.
Elsewhere, in Mississippi, at least 20,000 people were left without power as strong wind gusts caused power outages.
In the mid-west and north-east US arctic air tracking eastwards over the Great Lakes created this week a phenomenon known as lake-effect snow. Lake-effect snow occurs as a colder air mass spreads across a body of water. The layer of surface air above this water is then warmed, so its moisture-holding capacity is increased. This new, less dense, air then rises, cools and condenses, releasing the moisture as heavy snow on the lee side of the lake.
The outcome of this has been travel delays, as snow showers have continued to develop further eastwards.
At many central and European ski resorts, however, there has been a shortage of snow over the past month, with high pressure in charge. But a shift in weather conditions is occurring.
As arctic air, along with low pressure, begins to surge into continental Europe through next weekend, temperatures will plunge, with these parts of Europe and the Baltic states getting their first significant batch of snow for 2017.
