The Weather Map
Well before we had
weather maps we had experience which led to old wives tales, remember that “Red
Sky at night, Shepherds delight” was one of those?
Think about why it
came about and the implications concerning those shepherds.
Science has taken a
role in the development of knowledge
which we can use to our advantage.
Remember rule one! We
cannot YET change the weather, and activities especially in the UK are Weather
dependant.
The Science of
weather is NOT EXACT!
Where do we get the
Info? Weather stations all
around the world. They get it from recording data from fixed sites,
free balloons are released carrying radio Sondes and then share the
data with other units. Computer links and programs speed the
process around the world.
The old TV weather
chart seems to be a thing of the past and the new generation of computer
graphics is not all its cracked up to be.
Training and
knowledge can keep you ahead of the game so it's worth knowing what a cold
front is and what it means to you whether you are an aviator, golfer, sailor
or just having a picnic.
Let's start with the way the weather develops.
Moisture in air makes it lighter, (less dense)
(yes! Water molecules are smaller and lighter than the other gases they
replace);
Warmer air is lighter (hot-air rises, doesn't it?)
So warm, moist air is much lighter than the same amount of cold, drier air.
Warm, moist air exerts less pressure since it is
lighter.
Cool, dry air exerts more pressure since it is heavier.
Pressure regions
around the globe are defined as High pressure or Low pressure.
1013.2 millibars, or 29.92 inches if you are dealing in old money or are
American, is called a Standard pressure.
I have never been told but assume pressure above that is high and below is
low. I would need to check that fact …
Whatever it is a relative imbalance of pressure causes air to flow from high
to low pressure 4
Wind!
Big fall in
pressure 4big wind such as in a typhoon.
The area of Low
pressure is called a Depression.
Remember that
“Depressing” is bad and so is the weather.
Looking on a
weather chart lines of pressure are usually marked at 2 millibars
between each line.
If you see a map with lots of lines on then there is a big Low, or as we
learnt … Depression, so the weather is bad.
The other situation
is a map with few lines….less of a pressure gradient and the
weather can therefore be described using
the term SET FAIR!
With High
pressure in Europe the skies are clear with few clouds. In simple
terms you get a nice clear summer's day, or a cold crisp winter's day.
Climatology is
another branch of the science of weather so I will not delve too far into
that. Let's just hint that different things can mean the same, Typhoon
and Hurricane are the same deal, they just happen in different regions of
the world. So moving on …..as the adverts say better call your local
HSBC branch for local info.
In a Depression
….Bad weather brings clouds. The
clouds are formed when differing lumps of air meet up.
A cold air system from the Artic meeting with warm tropical air will force
the hot air to rise….condensation takes place and the more water vapour
in the air, the more clouds are formed.
So before we get too
heavy on this topic here's a tip:-
In general weather systems in the
Northern Hemisphere move from West to East due to the Earth's rotation.
Common sense tells us that what Ireland gets is coming our way soon.
Stewart Luck
Taking a look at a Weather Chart
|
 |
Conditions:-
High pressure over most of the UK (1039 mb is very high for summer),
which means 'heavy' dry air;
Widely-spaced lines (isobars) so light winds;
'Heavy' air so it gets stagnant and may become hazy;
Not much cloud so hot weather in summer, and frosty winter nights with
lots of stars visible.
But wait a bit - what's that out to the West, where our weather comes
from? That 'thumb-print is a depression. Enjoy the dry weather
while it lasts! If we are lucky the High pressure will push it North
of Scotland.
Thanks very much to the Met Office for the picture. |