Beware the deep midwinter: The current cold snap gives a chilling taste of what may lie ahead, Steve Ward writes

CAN YOU remember the last time we had a real winter, when frost flowers patterned the windows for weeks on end and the local lake was transformed into a scene from a Brueghel painting? Perhaps, though, snow in November may be a harbinger of things to come.

A run of mild winters, even in this Greenhouse Age, should have fooled no one. Winter's reputation has been continually renewed down the centuries. Maybe the next Big Freeze is just around the corner. The current cold snap suggests that it might be.

This year has proved an interesting one for meteorologists. Weather patterns have been disturbed and many places around the world have experienced torrential rain and floods. The recent upward temperature trend has faltered and in Britain a cool wet summer was followed by a cold wet autumn.

And all this against a background of the greatest explosion on the planet for more than 80 years. In June 1991 Mount Pinatubo, a volcano in the Philippines, blew itself apart and spewed gas and dust into the stratosphere, screening out the sun's heat and cooling the planet. Perhaps it is time to remind ourselves of the worst that winter can bring.

When rain turns to snow and frost grips the land, the world is transformed. All that is needed for this to happen is a change in the wind, as the past few days have dramatically shown.

Out to the west of Britain is a 3,000-mile-wide storage heater - the Atlantic Ocean, fed by the tropical waters of the Gulf Stream. If the top layer was cooled by only 0.1C to a depth of one metre, the heat released would be sufficient to raise the temperature of the air lying above it by 10C. Transported on a south-westerly wind, this bounty of the ocean will melt the snow in Moscow.

But when the prevailing wind fails to prevail, winter can move in on us with a vengeance.

Imagine a spring-like day in mid- winter. Drifts of leaves, yellowed and veined, decay in the hedgerows. Eager daffodils push up through the soil. And among the bare limbs of a gnarled oak, a blackbird is moved to song. Arms linked, an elderly couple stroll across bedewed grass and pause in the unexpected warmth of the pale January sun. The year is 1947.

What happened next is part of meteorological legend. A wind from east of Moscow brought back the Ice Age. For those who experienced it, the winter of 1947 was the winter.

Winter's worst struck when the country was least prepared, in the aftermath of war. When food and fuel were in short supply and rationing a fact of life, the weather succeeded where the Luftwaffe had failed. Britain was brought to a standstill, paralysed by non-stop blizzards, immense snowdrifts and freezing temperatures night and day. The army was drafted in to fight a new enemy.

During one exceptional spell in mid-February, the mercury remained continuously below freezing for two weeks and ice floes became a navigation hazard in the North Sea. Between 22 January and 17 March snow fell somewhere in Britain every day. From Dartmoor to the Highlands, farms and villages were cut off for weeks on end. The sun failed to shine.

Remarkable as the winter of 1946-47 was, in many respects that of 1962-63 surpassed it. Freezing temperatures set in before Christmas and by the evening of Boxing Day, deep snow blanketed the country. Many people would not see their gardens again until March. Moorhouse in the Pennines set a record with a five-week continuous freeze.

For temperatures to average below freezing through an entire month in Britain, as in February 1947, is a rare event. In two centuries there have been only about 20 such months. In 1963 there were two sub-zero months back to back. January 1963 was generally the coldest month in Britain since at least 1814; while to find a colder winter overall, you have to go back to 1740.

But the winters of 1947 and 1962-63 came nowhere near challenging Britain's record minimum temperature, which was set in 1895. The very cold and snowy winter of 1979 reached -24.6C, but it was 1981-82 that proved sensational.

On 12 December 1981, at Shawbury in Shropshire, the mercury fell to -23C, setting a new record low temperature for England. The next night the temperature, falling from a daytime maximum of only -12C, dropped to -24.9C. Only a month later and after a milder interlude, Shropshire again recorded Arctic temperatures. Newport established a new English record of -26.1C.

It takes a special kind of place to set records for winter cold: a frost hollow. On certain nights, when conditions are favourable, temperatures are turned upside down. When deep snow insulates the ground and the night is calm and clear, the air loses heat faster than a house without loft insulation. Cold air, being heavy, sinks down the hillsides and collects in valleys and hollows where the cold intensifies. Britain's frostiest frost hollow is the Scottish village of Braemar.

More than 1,000 feet above sea level, Braemar lies deep in the valley of the river Dee in Grampian and collects cold air from the 4,000-foot mountains. In the winter of 1981-82 Braemar came into its own. Every night for a week the mercury dropped below -16C and on five nights below -20C. 0n 10 January the Highland village equalled its own long-standing British record set in 1895. The minimum temperature was - 27.2C. The maximum was only -19.1C.

If the prospect of bleak midwinter makes you shiver in anticipation, I can offer some cold comfort. As an island, Britain can never experience the real extremes of cold possible on this planet, not unless the surrounding seas freeze over. The remotest frost hollow is no more than a couple of hours' drive from the ocean storage heater.

As the winter months approach, we can only speculate on what still lies in store. October blanketed parts of Scotland with the earliest snow for half a century and November's temperatures have tumbled to January levels. And while it might be comforting to know that we are not in the deep-freeze premier league, Britain's winter cocktail of raw cold and biting winds, howling blizzards and overcast skies, freezing fog and stinging sleet is in a league of its own.

The author teaches geography at a school in Sheffield.