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Introduction
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| Fig 1: Cars stranded in snow. |
Fig 2: Traffic on A30 at
Bodmin Moor |
| Snowfall caused 1,000 people to be stranded
in their vehicles in a six-mile tailback on the A30 road
at Bodmin moor for several hours on Friday 25 November
2005.
500 cars became trapped on the A30 at Bodmin Moor following
a crash which involved several dozen cars.
Helicopters and 4-wheel vehicles took stranded motorists
to stay in leisure centres overnight.
Teachers had to look after children after normal school
hours after they became trapped in schools.
68 of Cornwall’s 273 primary and secondary schools were
closed. |

Fig 3: Difficult driving conditions |
Areas affected
Impacts
| Peoples' health
and wellbeing
Despite the terrible conditions, the only injuries
to people involved a fire engine which came off the eastbound
A30 road on the way to answer an emergency call. One fire-fighter
was taken to hospital by helicopter with serious but not life-threatening
injuries.
Disruption to transport
Railway services were affected. Fallen trees on one of the
railway lines from London to Penzance caused trains to
be delayed.
People stranded at home/on the road/at
school
2,000 school pupils were stuck in schools and their teachers
had to look after them. Parents complained that it was difficult
to find out if their own children were safe and where they
were. Some school children were forced to stay at homes of
teachers and friends and in hotels.
A number of weather-sensitive outdoor events and some indoor
events such as pony show-jumping competitions were cancelled
on Saturday 26 November. | 
Fig 6: Snowbound vehicle |
Financial effects on
local economy
No exact figures are available for what the cost was, but
it is likely that the cost of the snow-event ran into several
hundreds of thousands or even millions of pounds for Devon
and Cornwall.
There was the cost of carrying out rescue operations
and setting up of emergency shelters.
The impact of people
not attending work and goods not being delivered to businesses
in the south-west of England is likely to have added to the
cost of the incident.
|

Fig 7: Train in snow |
Theory
Snow
Snow is a frozen type of precipitation. Precipitation also includes
rain, hail, sleet, fog etc. Snow normally occurs when precipitation
occurs and the air temperature at ground level is below about 2
°C. Snow is most common in the UK in the winter months. The snow
which affected the south-west of England on 25 November was an
unusual occurance in this month which is in the autumn season
(September 1 to November 30).
More information
Snow
Weather chart
Snow can occur when air reaches us from a northerly or easterly
direction, this helps to define the airmass.
| Figure 10 shows the weather chart at midday
on Friday 25 November 2005.
The blue arrows show the path
the Arctic air has travelled to reach south-west England.
Air is flowing anticlockwise around the area of low, so the
wind direction over the south-west of England is a northerly.
The airmass type is Arctic Maritime. This is a cold airmass
which often has periods of snow. The little cold front over
south-west England, shown by a line with triangles, indicates
where the snow is long-lasting and heaviest.
|  |

Fig 10: Weather chart for 1200 on 25 November
2005 |
| Satellite imagery
Figures 12 to 16 show visible satellite pictures from
1 p.m. to 5 p.m. on Friday 25 November 2005.
Alternatively, figure 11 shows an animation of the same
images.
The brightest white areas show where the thickest cloud
is and where snowfall is most likely to be falling. The
thickest cloud occurs over Bodmin moor at around 2 p.m.
and 3 p.m.
The satellite is sensing how much sunlight is being
reflected from the cloud. The darkening of the last image
is about the time of sunset at 5 p.m. The dark areas
of the picture over Exeter at 3 p.m. and 4 p.m. show
where the cloud has cleared.
|

Fig 11: Animation
of visible satellite images for 1-5 p.m.
on 25 Nov 2005
(click on the image for an animated version) |
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Fig 12: Visible satellite image for
1 p.m. on 25 November 2005
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Fig 13: Visible satellite image for
2 p.m. on 25 November 2005
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Fig 14: Visible satellite image for
3 p.m. on 25 November 2005
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Fig 15: Visible satellite image for
5 p.m. on 25 November 2005
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Fig 16: Visible satellite image for
5 p.m. on 25 November 2005
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| Radar imagery
Figures 18 to 25 show a sequence of radar imagery
from 11 a.m. to 6 p.m. on Friday 25 November
2005. Alternatively, figure 17 shows an animation of
the same images.
The legend, or key, shows the water equivalent in
millimetres (mm) per hour. 1 mm of water is about the
same as a 10 mm deep snowfall.
The radar imagery suggests
that the band of snow is moving westwards. It shows
that it snowed for most of the day over Bodmin Moor
before stopping around 6 p.m. It also suggests some
high rates of snowfall at times, shown by the pink
colours, e.g. 8.0-12.0 mm per hour. However, not all
of this snow accumulates as it can take a while to
settle on the ground. Also the radar does sometimes
overestimate the rate of snowfall. |

Fig 17: Animation of radar pictures
11-6 p.m. on 25 Nov 2005
(click on the image for
an animated version) |
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Fig 18: Radar picture for 11 a.m. on 25 November
2005
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Fig 19: Radar picture for
12 p.m. on 25 November 2005
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Fig 20: Radar picture for 1 p.m. on 25 November
2005
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Fig 21: Radar picture for 2 p.m. on
25 November 2005
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Fig 22: Radar picture for 3 p.m. on 25 November
2005
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Fig 23: Radar picture for 4 p.m. on
25 November 2005
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| Fig 24: Radar picture for 5 p.m. on 25 November
2005 |
Fig 25: Radar picture for 6 p.m. on
25 November 2005 |
| Air temperatures
Figures 27 to 32 show air temperatures from 12 p.m.
(midday) to 5 p.m. on Friday 25 November 2005.
Alternatively, figure 26 shows an animation of the same
images.
The temperatures of less than 1 °C (shown as yellow
and blue) indicate where it is cold enough for the
precipitation to most likely fall as snow.
The temperature remained below 1 °C for the whole
of this period on Bodmin Moor and over much of the
surrounding area. When the precipitation occurred,
it did fall as snow and, because the roads were so
cold, it was easy for it to settle on the A30 road
surface.
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Fig 26: Animation of
temperatures for 12-5 p.m. on 25 Nov 2005
(click on the image for
an animated version) |
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Fig 27: Temperatures at 12 p.m. on
25 November 2005 |
Fig 28: Temperatures at 1 p.m. on
25 November 2005
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Fig 29: Temperatures at 2 p.m. on 25 November 2005
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Fig 30: Temperatures at 3 p.m. on 25 November 2005
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Fig 31: Temperatures at 4 p.m. on 25 November 2005
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Fig 32: Temperatures at 5 p.m. on 25 November 2005
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| Snow depths
Figure 33 shows a map of snow depths from weather stations
taken at 9 a.m. on Saturday 26 November 2005.
Snow
depths tend to only be measured once per day at 9 a.m.
It is likely that, at the height of the event, snow depths
were greater, but that this may have melted overnight.
There may also be other locations, where there are no
weather stations, which had greater depths of snow. |

Fig 33:
Map of snow depths, in centimetres, from weather stations,
taken at 9 a.m. on 26 November |
| Figure 34 shows a satellite image for
1100 a.m. over the south west of England on Saturday
26 November 2005. The snow covered land surface is red,
uncovered land is green, and cloud is white. |
 Fig 34: Satellite image of snow
cover – red indicates snow |
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