After a bout of unsettled weather, Britain is poised to experience a spell of unseasonably warm weather, with temperatures predicted to reach 21C (70F). Weather maps are turning a glorious orange, signaling the arrival of what is being described as a "proper Indian Summer".

The Met Office defines an Indian summer as a warm, calm spell of weather occurring in autumn, especially in October and November. While the precise origins of the term are debated, it is believed to have originated in the eastern United States. It may have been linked to the practice of Indigenous Americans using the favorable conditions for hunting. The term gained popularity in the UK in the early 19th century.

This welcome change follows the passage of Storm Amy, which brought strong winds and heavy rain to parts of the country. As the storm subsides, a ridge of high pressure, sometimes referred to as a "Bermuda ridge," is expected to build, ushering in milder conditions.

Jim Dale, a meteorologist for British Weather Services, anticipates temperatures could reach 21C in the south of England, with the rest of the country experiencing temperatures in the mid to high teens.

The shift in weather patterns will bring variable cloud cover and the potential for overnight fog, which should clear by morning. The high-pressure system will keep Atlantic storms at bay for most of the country, although the extreme north may still experience some cloud and rain.

The unseasonably warm weather is attributed to a combination of factors, including a stable area of high pressure and the position of the jet stream. High pressure systems create settled conditions, while a shift in the jet stream allows the high pressure to dominate without disruption from Atlantic weather fronts. Sea temperatures around the UK are also still relatively warm from the summer months, which can help to moderate coastal temperatures.

While daytime temperatures are expected to be pleasantly warm, some chilly nights with isolated frost are possible. The Met Office indicates that temperatures will be near average overall.

This "Indian Summer" is expected to last from late September through October, and possibly into early November. However, the Met Office notes that towards the final third of October, there will likely be a transition to more unsettled conditions across the UK, and with a greater chance of rain, showers, and possibly strong winds.

Although the long-range forecast suggests a change in the latter part of October, for now, many Britons can look forward to a period of settled, warm weather, and a chance to enjoy the autumnal scenery.