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Who provides and presents the
UK's TV weather forecasts? |
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The Met Office provides information for most of the TV weather
forecasts in the UK. On many channels, including national BBC,
the presenters are Met Office staff.
More
about TV weather forecasts
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How accurate are weather forecasts? |
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Forecasts for 24 hours ahead are correct about six times out
of seven, and today's three-day forecasts are as accurate as one-day
forecasts were 20 years ago.
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But why aren't all forecasts
correct? |
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While weather forecasts are becoming ever more accurate, it is
still very difficult to predict the detailed differences in weather
at a local level.
To get the forecast right every time, forecasters would need
to have an accurate picture of the weather simultaneously from
every part of the world, as well as computers powerful enough
to calculate detailed minute-by-minute changes throughout the
forecast period. The Met Office has some of the most powerful
computers in the world, but there are limitations on how much
up-to-date data can be collected and processed. For example, there
are fewer observations over ocean areas than for populated land
areas, and the models need observations at multiple levels in
the atmosphere — not just on the ground.
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Why is the UK's weather so difficult
to forecast? |
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Mainly because of its location. A region's climate
is largely determined by its distance from the equator and proximity
to the sea. The UK has a huge ocean to the north and west (the Atlantic),
and a large continent to the south and east (Europe), meaning that
subtle changes in wind direction can bring marked changes in weather.
The UK also lies near the 'battleground' of warm air from the tropics
and cold air from the poles, which spawns the vigorous depressions
and quiet anticyclones that also bring marked changes in weather. |
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Do 'old wives' tales' have any
truth in them? |
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| The famous weather folklore about St Swithin's Day is only
a myth, but there is evidence that some other tales do have
sound meteorological substance. |
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St Swithin's Day if it do rain,
for 40 days it will remain.
St Swithin's Day if it be fair,
for 40 days will rain no more.
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For example, 'Red sky at night, shepherd's delight; red sky in the morning,
shepherd's warning' has a valid scientific explanation to support it.
It relates to the morning sun (rising in the east) illuminating the
clouds of approaching weather fronts on the western horizon (shepherd's
warning) and the evening sun (setting in the west) illuminating clearing
clouds on the eastern horizon (shepherds delight). As most poor weather
approaches the UK from the west and clears towards the east and because
sunlight at low levels appears red due to it being scattered by dust,
this ancient weather folklore is supported by science. |
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How are weather forecasts produced? |
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Before a weather forecast can be made, knowledge of the present
situation is essential. The many data sources used include satellites,
ships, aircraft, oil rigs, buoys and balloons, weather radar,
as well as manned land stations around the world. Automation often
assists or replaces the human observer and can provide information
from inhospitable and remote areas.
Traditionally, meteorologists have relied upon observations taken
near the Earth's surface using instruments (e.g. barometers, thermometers,
anemometers and rain gauges) and visual observations (e.g. cloud
and weather type).
Important sources of upper-air information are the balloon-borne
instruments (referred to as radiosondes) which provide information
about the temperature and humidity through the atmosphere. Satellites
have arguably become the single most important observational tool
for weather forecasters.
All data are then fed into computers and the weather forecasts are
based on the solution of a set of mathematical equations (a numerical
'model') describing certain physical processes in the atmosphere.
All national meteorological services worldwide share the observational
data free of charge.
Even with greater computer power, improvements to computer models
and other technological advances, there is still an important
role for human forecasters, who have to make allowances for the
computer model's known problem areas, such as its ability to handle
smaller features like rain showers or localised fog or mist. They
also have to take into account any late observations, consult
the latest satellite and radar pictures and use their own knowledge
of local topography.
Learn about the
weather
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What sort of computers are used
in forecasting? |
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Some of the most powerful computers in the world are used by national
met. services. In 2005, the Met Office again upgraded its systems
to one of the world's fastest supercomputers - the NEC SX-8. This
supercomputer doubles the computing power of the two existing NEC
SX-6 machines. This is roughly equivalent to 8,000 top-of-the-range
desktop PCs.
More
about computers at the Met Office
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How do I find out whether this
is the hottest/coldest/wettest day of the year? |
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Call the Met Office's Press
Office. Figures for the day can usually be confirmed at about
1900 hours, seven days a week. |
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Who decides whether it is a white
Christmas? |
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Usually this is determined by Met Office observers on duty at the
locations that are bet on by the public. Each bookmaker has different
criteria, but the usual definition is 'a flake of snow observed to
fall at a location anytime between 0001 and 2359 hours on 25 December'.
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Why do we use Celsius rather
than Fahrenheit? |
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| The Celsius scale is the World
Meteorological Organization standard for temperature measurement,
and is used throughout the world by the meteorological community.
The numbers are usually represented in text as, for example,
20 °C. You can say 'Twenty degrees C' or 'Twenty
Celsius'. |
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From Celsius to Fahrenheit,
F = (9/5 x C) + 32
From Fahrenheit to Celsius,
C = 5/9 x (F-32)
where C is the value in Celsius and F is the value
in Fahrenheit.
Example: convert 10 °C to °F.
9/5 x 10 = 18, add 32.
Answer = 50 °F
Example: convert 100 °F to °C.
100 - 32 = 68, then 68 x 5/9.
Answer = 37.8 °C
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Can you tell me the sunrise and
sunset times for...? |
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For information about sunset and sunrise times, and moon phases and
times you should e-mail
the Royal Observatory in Edinburgh who will be happy to answer
your enquiry. Alternatively, visit the Royal
Observatory's web site. They can also be contacted on 0131 668
8100, preferably between 2 p.m. and 4 p.m. Monday to Friday.
If you know your co-ordinates on the globe, then you can get an individual
print-out from the US
Navy web site which provides sun and moon times anywhere on the
globe. However, you should note that the times given are all in GMT
(otherwise known as UTC). Your latitude and longitude in the UK can
be found by entering your postcode on the Streetmap
web site.
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