Summer Set Fair

By early July the course of our summer can often seem set. If we have had a warm settled June water temperatures in our local seas may well have risen above normal and the weather pattern look set into a classic ‘blocked’ set up; the Azores high pressure may be well to the north of its usual position, extending well to the north east across the United Kingdom, with gentle south easterly winds pulling up some very warm air up from the heart of the sun baked European continent.

Conversely, we may have found that the unsettled weather we associate with a mobile Atlantic has not let up on us through June, bringing a regular supply of depressions, albeit weak ones, across us, more especially to the northern and western parts of the British Isles.

Such different patterns are a regular feature of our changeable patterns of weather across our maritime islands and the reason why those of us affected by the weather- which after all is probably most, if not all of us, in some way, should never be lulled into a sense of security that we really know what to expect from our summers on a year by year basis.

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History of the Weather

A short history of the weather

Since pre-historic periods men and women have looked to the sky and wondered what the weather was going to do- perhaps for planned hunting trip or drying pelts gathered from such a trip. Originally it was assumed that the sun ruled the earth’s weather and it was therefore worshipped as a god. Of course in many ways, arguably, we now know that premise to be more or less correct. It is worth remembering that during much of the Bronze Age period climatic conditions in the UK and Europe as a whole were much warmer than those we currently experience, allowing expansion and exploration northwards, although this trend was reversed during much of the cooler Iron Age period.

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Case Studies

Case study 1 Tropical Maritime airmass

This is probably the most common air mass that affects the British Isles, and it can do so at any time of the year, reaching it from near the Azores in the mid Atlantic Ocean, with low pressure to the north west and high pressure lying over France. Winds are south westerly and may be quite strong in winter. Having formed over relatively warm waters, it is also relatively mild or warm and very moist, at least in its lowest layers. As it approaches south-western and western parts of the British Isles it usually gives a lot of cloudy, damp weather with sea and hill fog. Although in winter it often stays dull and cloudy at low levels as the air mass crosses the country, in the summer insolation may be strong enough to dry out the air and warm it up quite substantially, giving some quite pleasant sunny weather by day in the eastern parts of both England and Scotland.

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Understanding Weather Processes

Understanding the weather map

One of the most important things anyone wanting to understand the weather can learn is how to recognise the salient features shown on a weather map.

The first thing a meteorologist will draw up on his or her chart (although nowadays nearly all maps are generated automatically by computers) are lines of equal pressure from observations. These are usually in millibars (mb) or sometimes inches.

We call lines joining points of equal pressure isobars. They are helpful because by creating them we can start to identify areas of high and low pressure at both the surface and aloft, that control our weather pattern. Pressure values are generally corrected to Mean Sea Level Pressure (MSLP) so that a standardised level can be shown, otherwise the observers height would affect the readings, as pressure decreases with altitude quite substantially.

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