Welcome to South Hereford Weather Station - Did you know ! About our Weather ?

Did you Know !!

Our Weather
IT’S SOMETIMES SAID that if the sun shines today, it’s weather, and if it shines for a year, it’s climate. This may be an over-simplification, but it’s basically true: when the weather forms a definite pattern over a period of time, you can begin to talk about climate.
Britain’s climate is temperate, meaning we rarely experience very hot or very cold temperatures. It is also maritime because of our proximity to the ocean. As a result we experience clear changes in the weather from season to season. Generally, Britain has warm summers, cold (though rarely very cold) winters, and long, coolish, unsettled springs and autumns. It’s a climate of variety, not extremes.
Nevertheless, although the average Briton may normally experience a small range of temperatures compared with the resident of Vladivostok, the British climate more than makes up for this in other ways.

UNUSUAL WEATHER CONDITIONS
Perhaps the most famous examples of unusual weather conditions in Britain are the harsh winter of 1962—3, and the long drought of the summer of 1976 and the great storm of October 1987. Each of these events broke new records, and established the weather as the subject of daily conversation, almost to the exclusion of everything else. Each event passed into popular mythology; and just as everyone old enough can remember what they were doing when President Kennedy was shot, so most Britons can recall where they were on Friday 16 October 1987, when the nation awoke to unprecedented devastation.
In fact, although generally the British climate is temperate, there is an astonishing variety in our geographical and seasonal changes, and record temperatures, as the table on the facing page shows.
It’s worth noting that the record high and low temperatures both occurred in the last two decades, as did the warmest and coolest summers — indicating that something strange may be happening to our climate, but more of that later (see The Future).

REGIONAL BRITAIN
There are wide regional variations in weather throughout Britain (as you can see from the table on the facing page). While the western and northern side of Britain is drenched in rain, the east and south-east is suffering the worst drought for almost three centuries. On average, Sty Head in the Lake District receives about 4300 mm (170 in) of rain each year, but St Osyth in Essex, roughly 500 km (300 miles) away, only has about 509 mm (20 in). As a rule of thumb, our rainfall tends to increase to the north and west.

Given the relatively small size of Britain, it’s surprising how regional our weather is. The key to this variety is our geography. The British Isles lie sandwiched between the north-west edge of the world’s largest landmass, Eurasia, and the Atlantic Ocean. So Britain is caught between the extremes of hot and cold weather from the Continent, and warm moist weather from the Atlantic.
Another reason for the range of weather is the variety of our landscape. The west is wetter than the east because of the high land stretching down the west of Britain. As air in Atlantic depressions hits the west side of Britain the air is lifted up over the high land, which increases the rainfall on the windward side of the high land (as shown in the diagram). As the air descends, a ‘rain shadow’ forms because the air has already dropped much of its water.
The more extreme weather tends to occur in mountainous regions where it is often cloudy, wet and windy. The weather in north-west Scotland is particularly severe because of the frequent passage of deep depressions.

The regional patterns for temperature are slightly different. The main factors determining the distribution of temperature are a place’s height, latitude and nearness to the coast, particularly the west coast — temperatures are lower inland than near the coast in the winter and warmer inland in the summer. In winter the coldest areas are parts of the Grampian and Tayside regions of Scotland, and the least cold are the extreme south-west of England and the Channel Islands. In July the warmest areas are around London and the coolest are parts of Scotland. Areas near the coast are less warm than inland areas, the opposite to winter, and the temperature decreases from south to north.

South-west and southern England is protected by the warm Atlantic, but on occasions Shrewsbury gets lower temperatures than Kent if the polar Continental airstream sweeps across England. The same applies to hot weather. The hottest air comes off the Continent and so Kent can be hot and dry when everywhere else in Britain is colder. If hot air does travel across Britain it makes places like Cheltenham very hot — the highest official temperature recorded in the United Kingdom was in Cheltenham on 3 August 1990, at 37. 10C (98.80F).
The western and northern parts of the British Isles also usually lie close to the normal path of the Atlantic depressions. Consequently their winters tend to be mild and stormy while the summers are wet and cool. Overall, the south of the British Isles is usually warmer than the north and the west is wetter than the east. The eastern lowlands of England have a climate similar to that on the Continent (drier, with a wider range of temperature than in the north and west). However, the winters are not as hard as on the Continent.
The severest thunderstorms roar into the south-east of
England. Some summer storms start by drawing hot air off the
Continental landmass. But they also pick up moisture as they
cross the Mediterranean or Bay of Biscay, and as they leave
France they only have a short hop across the English Channel

before they hit land again and reheat, triggering the thunderstorms. Cornwall also suffers from thunderstorms, especially during the daytime. It’s suspected that because Cornwall is a long peninsula with sea on three sides and air moving in from the sea over the land, it has a good feed of moist air for thunderstorms. If conditions are calm the storm stays in one place, which accounts for the most extreme local thunderstorms, such as at Camelford, Lynmouth in 1952 and Martinstown, Dorset on 18 July 1955 (see pages 98—9).
The impact of the weather on the way we live is quite marked. Agriculture on the west side of the country consists more of grasslands and rye which can tolerate wet weather, while the east side grows more cereals, such as oats, barley and wheat which needs less rain. The warmer weather in Kent supports fruit growing while the colder north supports hardier crops such as rye and oats. The south-west is warm and wet, and supports dairy herds and fruit growing in sheltered places. However, the severe drought of the east and south has now brought calls to pump the surplus water of the north and west over to irrigate farmland and replenish the reservoirs in the east and south of Britain.
Other local factors can give rise to unexpected variations in temperature and rainfall for places even a few miles apart. In big cities like London the average temperature is consistently 1—20C (1 .8—3.60F) warmer than the surrounding countryside. This is because buildings retain heat at night, and because of wasted man-made heat from buildings.
Other odd spots can be found where there are special landscape features. One of the coldest places in Britain is in Rickmansworth, just outside London. Normally as you move up hills the temperature falls, but if it is a good clear night in winter and a location is surrounded by long hill slopes all around then the cold air slides downhill just like water. Rickmansworth sits in amongst the Chilterns and the surrounding cold air spills down into the town and keeps it cold. The locality holds the lowest monthly average temperature in the whole of the United Kingdom, with — 80C (170F) recorded in December 1935. Such frost hollows are not uncommon.

Weather is closely related to pressure systems (and of course, subsequent airstreams) — recall how earlier it was mentioned that most of the simple home-type barometers have types of weather on their faces. One of these instruments is well worth having, to be warned of weather changes before they appear in your locality. There are four systems you need bother about.
To put you completely in the picture, in met terms the high pressure centre is usually known as a ‘high’ but officially it is called an ‘anticyclone’. The low pressure centre is usually known as a ‘low’ but is officially called a ‘depression’ — very apt as its weather is always depressing! How they form can be complicated enough but when they form is left to a ‘power from above’.

Depression
Let’s talk about ‘old misery guts first. Perhaps one way of explaining its formation is that air in the upper regions of the atmosphere can suddenly increase in speed and before the air behind it can catch up you can have a sort of ‘gap’ where temporarily there is relatively less air.
Remember when we talked about two glasses of water joined together? In this case, as Nature endeavours to equalise things, apart from a horizontal flow we would now have a vertical flow as the air from the surface ascends to fill the ‘gap’ taking place above. In this case it does so very gradually and in no way as fast as even the lightest wind. The result of the rising air is a decrease of pressure at the surface, thus producing a ‘low’ as we shall call it.
Next remember when we talked
about what happens to rising air? It cools, does it not? And, if it is moist enough, it can condense into water particles which eventually could grow into water droplets big enough to fall to Mother Earth.
Well with practically all lows this is just what happens. A low is therefore very much associated with bad weather capable of continuous rain/sleet/snow and high winds when it is known to be deep (or intense), that is, the isobars are close together. How long it will affect you depends entirely on how fast the centre is travelling and where you are located in relation to it. Sometimes it can be stationary which is not helpful if it is directly above you.
How do we know one is coming? The obvious answer is when a barometer is indicating a positive decline in pressure.

Trough
The trough, as the name implies, can produce a ‘pig of a day’ with the same sort of weather as its
‘parent’ low, except that being only a tongue it can pass over you more rapidly.
Anti-cyclone

Here we come to ‘sweetness and light’ — but not always. Being a ‘high’ it is the reverse of a ‘low’, which means it has air descending and increasing pressure at the surface. Again the reverse is happening so that instead of the air cooling on ascent, this air warms on descent and will then be capable of holding much more water vapour. The result is relatively little or no condensation taking place and therefore there can be little or no rain.
Here at times you can experience glorious summer weather with endless sunshine in a cloudless sky but plenty of haze reducing visibility. The magnitude of its favours depends entirely on its size, strength, and how fast it is moving in relation to you.
The winds are usually light but
steady and strong around the outer extremities.
In winter, this system can paint a very different picture. The cold air is much closer to condensation point than in summer and fog is quite on the cards — almost certainly in the late afternoon to early morning from late autumn to spring. As fog likes virtually calm weather the likelihood is even greater. If the sun should conjure up enough warmth the fog can be lifted to become low stratus cloud which, when it is forming a blanket totally covering the sky, produces a miserable but dry situation called ‘anti-cyclonic gloom’.
How do we know an anti-cyclone is coming? Once again the answer is when a barometer is indicating a
having said that, they can be quite positive increase in pressure.

Ridge
Similar to a trough, but this time being a tongue of high pressure, a ridge can produce anti-cyclonic weather but it will naturally not last as long as its ‘parent’ high. Also, you are unlikely to experience those dead calm spells that can come with

Lightning path
How do we know a thunderstorm is coming? The short answer to this is the appearance of cu-nimb clouds and a hot sticky unstable atmosphere — hence so many thunderstorms occur in the tropical regions. In the temperate zone during summer they are most likely to occur when a high, which has given you such lovely weather over a week or even more, begins to break down — a barometer check will tell you this before the sky does so.
In the above situation, a thunderstorm needs an unstable atmosphere —
where air can shoot rapidly from the surface into the upper air. But there can be the situation where the stable atmosphere associated with the declining high will have been great for trapping haze near the surface and therefore you may not initially notice the gradual build up of cu-nimb clouds in the distance at first — the visibility being poor due to the haze. A distant rumble might be the first hint you get. When it finally reaches you, make no mistake, the sky will be very different to what it has been in previous days.

There is another cloud type that gives an indication of potential thundery conditions being triggered off at medium level. It has the name of ‘alto-cumulus’ and forms in a stable atmosphere, but when the suffix ‘cas’ is added (real name ‘castellanus’) it means that medium level instability is developing. There are two interesting foibles about alto-cu cas (Ac cas).
First, when it appears in the sky it does not mean that a thunderstorm will necessarily develop at that location
but usually one will occur within a hundred-mile radius. Second, it used to be called ‘castellatus’. For years I used this name until reprimanded one day. It appears that unknown to me the name had changed; on asking why I was told someone must have done it but no one knows whom’!
One way or another, thunderstorms are not pleasant but for those who cannot bear a heat wave they are a blessing. Now to some of the extremes in weather.

Violent Weather Thunderstorms
When ice particles in a cu-nimb c loud join together to form hailstones, as they rage up and down in the strong currents within this type of cloud an electrical charge is created which, when it becomes intensely powerful, breaks away to find earth (the electrical one). This break-away is called lightning and can be in two forms.
When its target is the ground it will be visible in a zig-zag pattern known as fork lightning. Should the target happen to be within another cu-nimb close by it will not been seen as a zigzag as it travels within the clouds from one to the other. It will vividly illuminate them, whereupon it is called sheet lightning. The frightening clap of thunder associated with the lightning is caused by what can best be described as the explosion that comes about due to the effect of the lightning’s intense heat on the immediate surrounding air.
the said ‘parent’ but you could be free from the winter fog or ‘gloom’ mentioned above. The ridge is usually a break between two frontal systems. Frontal systems play a major part in weather and are explained in the following chapter.