When high pressure dominates the UK weather as it has done this past week, many expect crisp blue skies and sunshine.
But as seasoned forecasters know, especially in the colder months, high pressure can bring something quite different: anticyclonic gloom.
This term, increasingly popular in media and public discourse, describes a paradoxical weather pattern where high pressure leads not to brightness, but to persistent grey skies, mist, fog, and drizzle. It’s a phenomenon that’s both meteorologically fascinating and socially impactful, affecting everything from hanging the washing out to public mood.
What Is Anticyclonic Gloom?
Anticyclonic gloom occurs when a high-pressure system settles over the UK, creating a stable atmosphere that suppresses vertical air movement. This stability traps moisture and low-level cloud, preventing the usual mixing that would disperse fog and allow sunshine to break through.
Instead of the uplifting weather often associated with high pressure, we get:
- Stratus and stratocumulus clouds lingering for days.
- Light winds, which fail to clear the cloud.
- Low sun angles, especially in autumn and winter, which lack the strength to burn off the gloom.
- Surface moisture condensing into fog and drizzle.
READ MORE: Met Office 10-Day Trend: High pressure dominating, but for how long?
The result is a blanket of dull, grey weather that can persist for days, particularly in inland areas and valleys where cold air pools and fog becomes entrenched.
November 2024: A Textbook Example
The first half of November 2024 was a classic case of anticyclonic gloom. A robust high-pressure system over continental Europe extended its ridges across the UK, locking in a stagnant air mass for over ten days.
During this period:
- Virtually no sunshine was recorded in many locations.
- Temperatures remained mild, but the atmosphere was saturated with mist, fog patches, and drizzle.
- Dense fog was widespread and persistent, particularly in low-lying areas.
- On the 6th, sites across England, Scotland, and Northern Ireland recorded record-breaking maximum temperatures, despite the lack of sun.
This paradox, mild temperatures with no sunshine, underscores the complexity of anticyclonic gloom. It’s not cold and stormy, but it’s far from pleasant.
Why does it happen?
The mechanics of anticyclonic gloom are rooted in atmospheric physics:
- High pressure causes air to sink, warming it slightly and compressing it.
- This sinking motion inhibits cloud dispersal, especially when the air near the surface is moist.
- Radiative cooling overnight leads to fog formation, which then struggles to lift during the day.
- Lack of wind means pollutants and moisture accumulate, reinforcing the gloom.
In summer, high pressure often leads to sunshine because the sun is strong enough to burn off cloud. But in winter, the sun’s lower angle and shorter duration make it ineffective against the entrenched cloud layers.
READ MORE: The UK land observation network: Underpinning weather and climate understanding
Why it matters
Anticyclonic gloom isn’t just a meteorological curiosity, it has real-world implications: Forecasting challenges arise, as cloud behaviour under high pressure is difficult to model accurately. Transport and aviation can be disrupted by persistent fog, especially in busy corridors like the Midlands and southeast England.
For weather communicators, it’s a term that resonates. It captures the paradox of dull weather under high pressure, helping the public understand why a “good” forecast can still feel gloomy.
From Gloom to Storms
Interestingly, the gloom of early November 2024 gave way to dramatic weather later in the month. As the high pressure retreated westward, depressions moved in from the north, bringing snow, frost, and eventually storms.
On the 23rd, Storm Bert swept across the UK with rainfall totals exceeding 120mm in parts of England and Wales, and gusts reaching 80mph over northern Wales and the south coast. Just days later, Storm Conall brought more wind and rain to southern England.
This transition from anticyclonic gloom to active storm systems illustrates the dynamic nature of UK weather, and the importance of understanding the subtleties of high-pressure systems.
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