Weather in the British Isles

What Weather in the British Isles covers

Weather in the british isles is examined in Unit AS 1, Physical Geography. It covers how precipitation forms, air masses affecting the British Isles, the polar front and the birth of a depression, the life cycle of a depression, and its fronts, the sequence of weather as a depression passes, anticyclones in summer and winter, isobars, wind, and the front symbols on a synoptic chart and station circles, recognising systems, and satellite images.

The 8 subtopics

Each one has its own page. CCEA AS Geography students sit this topic in the first year.

• How precipitation formsDew point, stable and unstable air and how orographic or relief precipitation forms.Open →
• Air masses affecting the British IslesWhat an air mass is and how it is named, why it changes character as it travels, and the source region, track and weather of each type that reaches the British Isles.Open →
• The polar front and the birth of a depressionWhat the polar front is, where the jet stream sits above it, how a kink in the front becomes a depression, and why depressions arrive in families.Open →
• The life cycle of a depression, and its frontsFirst stage in the life cycle of a depression, mature stage of a depression and cold occlusion and a warm occlusion.Open →
• The sequence of weather as a depression passesHow pressure, temperature, wind, cloud, precipitation and visibility each change at a station as a whole depression passes overhead.Open →
• Anticyclones in summer and winterSurface winds in an anticyclone in the Northern Hemisphere, blocking anticyclone and why does it matter and weather of a summer anticyclone in the British Isles.Open →
• Isobars, wind, and the front symbols on a synoptic chartSynoptic chart and letters L and H.Open →
• Station circles, recognising systems, and satellite imagesReading wind, cloud and weather off a station circle, telling a depression from an anticyclone on a chart, and what visible and infrared satellite images each show.Open →

What you need to know

Answer each one before you reveal it.

Take Weather in the British Isles further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Depression vs Anticyclone

  Depression: an area of low pressure with rising air and unsettled conditions. Anticyclone: an area of high pressure with sinking air and settled conditions.

• Veering vs Backing

  Veering: the wind changing direction clockwise. Backing: the wind changing direction anticlockwise.

• Warm front vs Cold front

  Warm front: the leading edge where warm air rises gently over cold. Cold front: the trailing edge where cold air undercuts warm steeply.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is precipitation, and in what forms does it reach the ground?

   Model answer

   Precipitation is any form of water, liquid or solid, that falls from cloud and reaches the Earth's surface. It includes drizzle, with droplets under 0.5 millimetres, rain, sleet, which is partly melted snow, snow, and hail, which is layered ice formed in vigorous cumulonimbus updraughts. Dew and hoar frost are not precipitation, because they condense directly onto surfaces rather than falling from cloud.

2. 2

   What has to happen before precipitation can fall?

   Model answer

   Air containing water vapour must be made to rise. As it rises it expands and cools, and once it has cooled to its dew point it is saturated. The vapour then condenses onto tiny hygroscopic condensation nuclei such as dust, salt or pollution particles to form cloud droplets. Those droplets must grow large and heavy enough, by colliding and coalescing or by ice crystals growing at the expense of supercooled droplets, to overcome the updraught and fall. Remove any one of these stages and there is no precipitation.

3. 3

   What is the dew point?

   Model answer

   The dew point is the temperature to which a parcel of air must be cooled, at constant pressure, for it to become saturated, that is for its relative humidity to reach 100 per cent. Cooling it any further forces condensation. Warm air can hold far more moisture than cold air, so it can reach a much higher dew point, but the dew point of any particular parcel depends on how much vapour it actually holds: warm dry air has a low dew point, and saturated air has a dew point equal to its own temperature.

4. 4

   What is relative humidity and why does it rise as air is lifted?

   Model answer

   Relative humidity is the amount of water vapour actually in the air expressed as a percentage of the maximum the air could hold at that temperature. Lifting the air does not change how much vapour it contains, but the air expands and cools, and cooler air has a smaller capacity. The same quantity of vapour therefore represents a larger fraction of a shrinking capacity, so relative humidity climbs until it reaches 100 per cent and condensation begins.

5. 5

   What is the dry adiabatic lapse rate and why does it have the value it does?

   Model answer

   The dry adiabatic lapse rate is the rate at which a parcel of unsaturated rising air cools purely because it expands into the lower pressure around it, with no heat exchanged with its surroundings. It is close to 10 degrees Celsius per 1000 metres. A descending unsaturated parcel warms at exactly the same rate as it is compressed.

6. 6

   What is the saturated adiabatic lapse rate and why is it lower than the dry rate?

   Model answer

   The saturated adiabatic lapse rate is the rate at which a parcel of air that has already reached dew point cools as it continues to rise, and it is roughly 5 to 7 degrees Celsius per 1000 metres. It is lower than the dry rate because condensation is taking place inside the parcel and releases latent heat, which partly offsets the cooling caused by expansion. This is why saturated air, once it starts to condense, can keep rising more easily.

What is inside Levo

Six ways to work the same material.

Weather in the British Isles revision questions

Is Weather in the British Isles examined at AS in CCEA Geography?

Yes. It sits in Unit AS 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.

What does Weather in the British Isles cover in CCEA AS-Level Geography?

8 subtopics: how precipitation forms, air masses affecting the british isles, the polar front and the birth of a depression, the life cycle of a depression, and its fronts, the sequence of weather as a depression passes, anticyclones in summer and winter, isobars, wind, and the front symbols on a synoptic chart and station circles, recognising systems, and satellite images. Each one has its own page with questions and model answers.

How is Weather in the British Isles organised?

By the CCEA 3910 specification, subtopic by subtopic, so it matches the order you are taught it in.