CLEAR SKIES CAUSE FROST HIGH PRESSURE High Pressure means that air tends to sink. Sinking air is compressed, warms up as a result and its relative humidity falls below saturation. Any clouds evaporate. Rainfall is unlikely, apart from occasional short, intense convectional storms due to insolation with lack of clouds in daytime. � In Britain, high pressure systems have clear skies, little or no wind, little rainfall and tend to be stable and slow moving. � Visibility is intially good, but rapidly deteriorates as dust is trapped by sinking air and is not washed out by rainfall. � Cloud cover is slight, resulting in a high diurnal ranges of temperature (hot days, cold nights). Due to the trapped dust particles and cold nights, dew, frost, fog or smog are common. � Air quality is low as all forms of pollution are retained in the lower atmosphere. FEW CLOUDS VISIBILITY IS POOR FOG & SMOG IS COMMON VISIBLITY REMAINS BETTER IN MOUNTAINS - LESS POLLUTION CLEAR SKIES LITTLE WIND

Credit 03 Credit 03

How to answer …… A Weather Question

How to answer …… A Weather Question

Synoptic Chart for the British Isles at 0700h on 31 August A yacht race from Wick to Stornoway was due to start from Wick harbour at 8.00am on 31 August At 7.00am the Met Office advised the race organisers to cancel the race. With reference to the synoptic chart, explain why this advice was given. 5 marks

A yacht race from Wick to Stornoway was due to start from Wick harbour at 8.00am on 31 August At 7.00am the Met Office advised the race organisers to cancel the race. With reference to the synoptic chart, explain why this advice was given. 5 marks What are the key words? place : see map direction : see map time : compare with map type of boat : think! change of plan! use the information on the map number of points to make

Link question to the map Where? 0700 h 31 August When? Wick and Stornoway From Wick to Stornoway Direction? Race due to start at 0800h Map is for 0700h

Study the map for information Centre of low pressure : likely to bring stormy weather Occluded front: broad belt of very heavy rain, low cloud and poor visibility Tightly packed isobars : strong winds South westerly winds Associated weather is moving west to east Warm mT air Cold mP air

Back to the question …. Why was the race cancelled? Competitors would risk very strong winds and therefore high seas Competitors would risk very strong winds and therefore high seas They would be sailing straight into the wind so it would be difficult to make progress They would be sailing straight into the wind so it would be difficult to make progress Temperatures would be low Temperatures would be low There would be heavy rain There would be heavy rain There would be thick cloud and probably poor visibility There would be thick cloud and probably poor visibility But this is not enough. Why not?

“Explain.. With reference to the map” Strong winds – close isobars Strong winds – close isobars Head winds – wind direction SW Head winds – wind direction SW Low temperatures – mP air mass Low temperatures – mP air mass Heavy rain – occluded front Heavy rain – occluded front Low cloud and poor visibility – occluded front Low cloud and poor visibility – occluded front 5 marks

Study the synoptic chart below and describe the likely weather conditions in Glasgow (G) and Lyon (L)

Miss Anything? remember to include wind, rain and temperature. What type of air pressure are they experiencing? Look at the spacing of the isobars. Glasgow will be experiencing periods of heavy rain with a short dry period in between. The winds will be high. Glasgow will be experiencing periods of heavy rain with a short dry period in between. The winds will be high. Lyon will be experiencing dry, sunny weather with clear calm skies. There will be low temperatures and possibly frost. Lyon will be experiencing dry, sunny weather with clear calm skies. There will be low temperatures and possibly frost.

Other topics to revise Air masses Air masses Weather instruments Weather instruments Station circles Station circles HP and LP HP and LP

Each of 4 zones has issues: Deforestation in the RAINFOREST Deforestation in the RAINFOREST Desertification in the DESERT Desertification in the DESERT Oil development in the TUNDRA Oil development in the TUNDRA Tourism in the Mediterranean and ocean pollution. Tourism in the Mediterranean and ocean pollution. LOOK over notes and check LOOK over notes and check