UK Met Office Issues Amber Warning for Extreme Heat Ahead of Heatwave

The Met Office has issued an amber weather warning for extreme heat across parts of the UK, ahead of a significant heatwave expected this week.

The warning, covering the South West, South East, the east of England, and sections of south Wales, will be active from 1am on Monday until the end of Tuesday. Forecasters predict the developing hot spell could lead to widespread impacts on people and infrastructure.

Meteorologist Max Deakin stated that temperatures could potentially reach the mid-thirties next week, following what is anticipated to be a very warm weekend for many.

The unseasonably hot weather is being driven by a significant area of trapped high pressure building in Europe, known as a ‘heat dome’, which is triggering scorching temperatures across the continent.

Here we explore what causes a heat dome and how a heatwave is defined.

What is a heat dome?

A heat dome is created when a high pressure area stays over the same area for days or potentially weeks, trapping very warm air underneath it, like a lid on a saucepan. Because hot air expands, it creates a ‘dome’ that bulges out.

This weather phenomenon causes temperatures to become hotter and hotter, building through the day and rise above what is considered normal, since warm air becomes compressed over a smaller region.

The ground warms as well and moisture evaporates, the RMS says, making it easier for temperatures to continue to rise.

These weather systems and their prolonged heat also increase the risk of wildfire and heat-related health problems, the Royal Meteorological Society (RMS) said.

Often these pressure systems move east to west, the RMS explains. Sometimes they can be blocked when the jet stream of strong winds high in the atmosphere weakens.

Large parts of central and northwestern Europe will be covered by these conditions the coming days, with temperatures expected to reach around 10C above mid-June averages, according to the Met Office.

Spain, France and Italy will see temperatures rise well into the 30Cs, and some areas could exceed 40C.

The UK will see a more varied and complex pattern, as the warm air from Europe attempts to move northwards and contrasts with low pressure in the northwest. This means northern and western parts of the UK will likely see repeated spells of rain due to the cooler weather front, while southern and eastern areas will see temperatures rise steadily.

What is the definition of a heatwave?

A heatwave is simply a prolonged period of abnormally high temperatures. What is considered an abnormally high temperature varies from place to place.

Several countries issued heatwave alerts ahead of the weekend including Spain, which experienced temperatures of up to 42C in parts.

In France, the meteorological office has issued an orange heatwave alert for nearly the entire country with temperatures expected to reach “scorching levels”.

In Mediterranean cities and towns, the French meteorological office expects temperatures of up to 40C, while only regions near the English Channel and the border with Belgium will experience temperatures below 34C. Paris is forecast to reach 37C on Monday and Tuesday.

Lisbon is forecast to reach 41C on Monday, while temperatures in Rome are expected to peak at 37C on Wednesday and Thursday.