Transcript revision weather

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.
LITTLE
WIND
CLEAR SKIES
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.
�
VISIBILITY IS
POOR
FEW CLOUDS
CLEAR SKIES CAUSE FROST
VISIBLITY REMAINS BETTER IN
MOUNTAINS - LESS POLLUTION
FOG & SMOG IS
COMMON
•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
What are the key words?
type of boat : think!
place : see map
A yacht race from Wick to
Stornoway was due to
start from Wick harbour
time : compare at 8.00am on 31 August
direction : see
map
with map
At 7.00am the Met Office
advised the race organisers
to cancel the race.
change of plan!
use the
information
on the map
With reference to the
synoptic chart, explain why
this advice was given.
5 marks
number of points
to make
Link question to the map
0700 h
31 August
Where?
Wick and Stornoway
Direction?
From Wick to Stornoway
When?
Race due to start at 0800h
Map is for 0700h
Study the map for information
Occluded front:
broad belt of
very heavy
rain, low cloud
and poor
visibility
Cold mP air
Tightly packed
isobars : strong
winds
South
westerly
winds
Associated
weather is
moving west
to east
Centre of low
pressure :
likely to bring
stormy
weather
Warm mT air
Back to the question ….
Why was the race cancelled?
• 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
Temperatures would be low
There would be heavy rain
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
• Head winds – wind direction SW
• Low temperatures – mP air mass
• Heavy rain – 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.
• 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
• Weather instruments
• Station circles
• HP and LP
Each of 4 zones has issues:
• Deforestation in the RAINFOREST
• Desertification in the DESERT
• Oil development in the TUNDRA
• Tourism in the Mediterranean and ocean
pollution.
• LOOK over notes and check
• http://www.scalloway.org.uk/phye1.htm