The characteristics of anticyclones and the contrasting summer and winter weather they bring to the British Isles (AO1, AO2).

What this dot point is asking

CCEA pairs the depression (low pressure) with its opposite, the anticyclone (high pressure). You must explain what an anticyclone is, why high pressure brings calm, settled, dry weather, and crucially how that settled weather feels completely different in summer and in winter. The same pressure system gives hot, sunny days in July but frost and fog in January, and explaining that contrast is the key AO2 skill.

What an anticyclone is

Why high pressure means settled weather

The logic runs in a short chain you should be able to recite.

1. Air sinks in the high-pressure centre.
2. Sinking air warms and dries, so condensation cannot happen.
3. No condensation means little cloud and clear skies.
4. The gentle pressure gradient means light winds, so the weather is calm and settled.

Because depressions cannot easily push in, anticyclonic spells are persistent, which is why a settled period of weather often lasts several days.

Summer anticyclones

In summer the clear skies let the high sun heat the ground strongly.

• Hot, dry, sunny days with light winds and good visibility.
• Cool nights are still possible because clear skies allow heat to escape after dark, sometimes forming morning dew or mist.
• A long-lasting anticyclone can cause drought and water shortages, and intense heating can trigger afternoon thunderstorms as the air rises locally.

Winter anticyclones

In winter the sun is weak and the nights are long, so the same clear skies cool the ground rapidly.

Worked example: same system, two seasons

Common mistakes

Examples in context

Example 1. The blocking high and a heatwave. When an anticyclone parks itself over the British Isles in summer, it can block Atlantic depressions for a week or more. Day after day of cloud-free skies bakes the ground, reservoirs drop and hosepipe bans follow. The persistence of the high, not just one sunny day, is what turns settled weather into a drought, which is exactly the kind of impact CCEA asks students to explain.

Example 2. Freezing fog grounding flights. On a calm, clear winter night under high pressure, heat radiates away and the cold, still air near the ground reaches its dew point, forming dense freezing fog. With no wind to disperse it, the fog can sit over airports all morning, disrupting flights and roads. This links the anticyclone's clear skies and light winds directly to a real human impact.

Try this

Q1. In which direction do winds blow around an anticyclone in the northern hemisphere? [1 mark]

• Cue. Clockwise, outwards from the high-pressure centre.

Q2. Explain why anticyclones bring clear skies. [2 marks]

• Cue. Sinking air warms and dries, so water vapour cannot condense and little cloud forms.

Q3. Why do winter anticyclones bring frost and fog? [3 marks]

• Cue. Clear skies and long nights let heat escape, cooling the ground below freezing, while calm moist air forms freezing fog.