The Met Office has provided an explanation for a common yet often misunderstood winter weather phenomenon known as 'anticyclonic gloom'. This term describes the persistent, dreary conditions of grey skies, mist, and fog that can dominate the UK's weather during periods of high pressure, particularly in the colder months.
Anticyclonic gloom occurs when a high-pressure system settles over an area. While high pressure is often associated with clear, settled weather in summer, its effects are quite different in autumn and winter. During these seasons, the sun's lower angle and weaker intensity mean the ground cools significantly overnight. When a high-pressure system is present, it creates stable atmospheric conditions, preventing air from rising. This stability traps moisture, pollutants, and tiny water droplets close to the ground, forming extensive layers of stratiform cloud, mist, or fog.
This trapped layer of cloud acts like a blanket, reflecting what little sunlight there is back into space and preventing it from reaching the surface. Consequently, temperatures remain low, often hovering around 0°C to 5°C, and the air feels damp and raw. Wind speeds are typically very light, often below 10 mph, contributing to the stagnant feel of the air. The lack of air movement means that any pollutants emitted, particularly in urban areas, can accumulate, leading to poorer air quality alongside the visual gloom.
Across the UK, anticyclonic gloom can affect different regions. In England, particularly the Midlands and parts of the South East, it can lead to prolonged periods of fog and low cloud, sometimes lasting for days. Scotland and Northern Ireland may also experience widespread mist and low cloud, especially in sheltered valleys and coastal areas. Wales, with its varied topography, can see significant differences, with higher ground potentially breaking free of the cloud into brighter skies, while valleys remain shrouded.
The impact of anticyclonic gloom extends beyond just the visual. The persistent lack of sunlight can affect mood and wellbeing, a phenomenon often linked to Seasonal Affective Disorder (SAD). For drivers, reduced visibility due to fog and mist presents significant hazards, requiring extra caution on roads. The cold, damp air can also exacerbate respiratory conditions for vulnerable individuals. While there are no specific warnings for 'gloom', the Met Office issues yellow warnings for fog when visibility is expected to drop below 200 metres, which is a common feature of this weather type.
Understanding anticyclonic gloom helps explain why some winter periods feel relentlessly grey and cold, even without strong winds or heavy precipitation. It is a natural consequence of the interplay between high-pressure systems and the UK's geographical position and climate during the colder, darker months.
Source: Met Office