We’re just entered Spring – which is a time of year where the weather is especially unreliable. In this article, we’ll examine this season, and consider what meteorological surprises it might spring upon us.
In Britain, the climate is temperate. This means that the temperature is neither very hot nor very cold – however much the British might grumble about it. In London, the average annual temperature is around ten degrees Celcius – but this figure varies only by around seven degrees throughout the year.
In Springtime, we’re moving toward this average (and indeed, beyond it as we progress toward summer). The average minimum temperature is between four and eight degrees, while the maximum runs through the mid-to-high teens.
That said, this is a time of year where the Atlantic has already lost much of its heat (more on that later), and so the British spring depends entirely on direct sunlight. If it’s a cloudy day, then you can expect it to be cold outside.
While the season is predominantly dry, we can expect heavy intermittent showers later in April and May. In some cases, thunderstorms descend – but these storms are nowhere near as powerful as their counterparts on the continent.
Why is this the case?
Latitude is among the foremost influencing factors when it comes to the temperature on the ground. Broadly speaking, the nearer on planet Earth you are to a pole, the colder you’ll be, while the nearer to the equator you are, the warmer you’ll be. In the Northern Hemisphere, it’s the north that’s cold, while the south is warm. This is true on a planetary scale, but it’s also true if you zoom into the geography of a specific small landmass like the British Isles. The temperatures we seen in northern Scotland, then, are generally cooler than those we’d find in the south of England.
This is because of the angle of insolation. At northerly latitudes, sunbeams strike the earth at a different angle. Their effect is therefore spread over a greater area, and is much less potent.
Of course, latitude alone cannot explain the temperature in Britain. After all, we’re at the same latitude as Alberta, Canada, whose residents have to endure winters of minus fifty degrees, and annual snowfall that’s sufficient to bury a small car. Clearly, there are other factors at work.
Climate, after all, is determined by a myriad of intertwining forces, each exerting a small amount of tug on the others. And in Britain, the effect of the enormous body of water surrounding us cannot be understated.
The sea affects the climate in Britain in two main ways. Firstly, it acts as an enormous heat sink. When sunlight strikes the sea, it warms it. This heat energy stores up during the summer, and releases during winter. This helps to blunt the edges of the summer and winter temperature extremes. This is why the west coast of the UK and Ireland are generally colder than the east, thanks to the influence of the Atlantic.
The second mediating effect comes courtesy of the Gulf Stream, a warm current of water which carries water from more equatorial climates. This current is around seven degrees warmer than the surrounding water, and goes a long way toward heating Britain during the winter.
We should also consider the effect of altitude. As everyone knows, mountaintops are much colder than plains – that’s why they’re capped with snow during the winter (and often, all year round). But why should this make a difference to the temperature? Well, the air pressure is reduced at altitude, because of the reduced weight of air overhead. This means that air molecules are less likely to collide and produce warmer temperatures.
The British Isles, for the most part, are rather flat. There are no mountains which even approach the heights of those on the European mainland. The only partial exceptions to this rule lie in the Scottish Highlands. These peaks have a tremendous say in the local climate, and combine to create winters that are far colder than those endured just a few miles south. If you’re planning a hiking trip in Scotland, then, you should be prepared for chilly weather.
Finally, it’s worth considering the direction of the wind. Generally speaking, when the wind is blowing from the south, it will bring with it warm air from the equator. When it’s blowing from the north, it will bring with it the cold air from the Arctic.
Of course, now that we know what to expect from the British spring, we’re still left with a decision to make about it. If you’re out and about in Britain, particularly if you’re making a trip through the countryside, then you’ll need a range of products at your disposal to cope with the range of possible weather conditions. Since the temperature is so influenced by cloud cover, and the rainfall so intermittent and unpredictable, it’s wise to pack a waterproof coat, and possibly an umbrella – as well as a t-shirt for when the weather picks up.
In very early Spring, snowfall is not-unheard of, and temperatures can still drop to below freezing during the night, making an ice-scraper a worthwhile addition to your backpack. This year, however, we seem to have moved beyond that possibility.