August
2003
The heat is on - statistically speaking
By BBC Weatherman David
Braine |
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| You
could become a Spotlight weather watcher |
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Hotter
than the summer of 1990... how do we know? I've been asked many times,
how do we know how hot it is, how cold, who had the most rain, and
especially with August's heat-wave, how do we establish if it's a
record or not? |
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It was
Benjamin Franklin who first realised weather moved and that weather
observations in one place could help predict what the weather might
do somewhere else.
Today, forecasting the weather is very complicated, covering small
scale events such as light showers - to the largest scale like global
warming.
To cope with these problems, a world-wide solution is needed: a network
of weather observing stations.
Feeling Hot, Hot, Hot
Just as you would take the temperature outside or look at the
barometer to get a reading from your garden, so do millions of other
people all over the world.
Under the guidance of the World Meteorological Organisation (WMO)
based in Geneva in Switzerland, every hour in every country around
the world weather observations are made and sent via computer or telephone
to various hubs and then onto the forecasters and their computers.
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| Measuring
rainfall |
Weather
observations on land, sea and in the air are received in a standard
code and include temperature, pressure, wind and rainfall amongst
the readings.
These readings are from standard instruments, all taken in the same
way all around the world. The WMO sets these standards and guidelines.
Most of the instruments have to be placed in a weather screen, called
a Stevenson screen, which looks a bit like a beehive.
These shade the thermometers from direct sunlight and, with louvered
doors, make sure only a gentle wind can blow over them.
As a result, all the temperature readings around the world can be
directly compared to each hourly observation of the many millions
taken under the same standard conditions.
So if your thermometer over the last few days recorded 104F and yet
the highest was 95F (officially) in your area it may be because it
was exposed to direct sun or was near concrete etc.
Wind is measured using an anemometer. The anemometer cups have to
be a standard 10 metres above the ground and at least 10 times the
height of any obstruction away from it.
There are similar strict guidelines on how to measure rainfall, snow,
and so on.
Man Over Machine
Over recent years there's been a move to automate weather observations,
with some partial success.
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technology doesn't account for some of the human factors |
Up until
quite recently the human input was considered important, with the
observer checking all the parameters including cloud height, type
and structure, as well as describing the weather, for example light
drizzle or haze.
Unfortunately, doing away with the human input (a cost-saving measure)
means these important parameters can no longer be observed.
Weather Watching
Across the South West there are only a fraction of the 'old style'
observing stations left. So often when looking at the automated stations,
the forecaster is missing some of those important little bits of additional
information.
As technology advances we'll eventually have webcams and visiometers
(laser visibility measuring devices), but for the moment we don't….
making life for the forecaster much more difficult.
In fact with computer model products and increased automation we are
in danger of losing the most important forecasting tool, our own eyes.
You can't forecast anything unless you know what the weather is like
right now.
One of the ways you can help is to let us know of the weather
conditions where you live. If you have a weather station and regularly
take readings why not become one of our local weather watchers.
To find out more, send me an email: spotlightweather@bbc.co.uk |
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