Call this May? What is wrong with the weather?

Ground frost, late blossom, icy winds but no rain: it's all down to a freakish failure of the prevailing winds, writes Geoffrey Lean

It's a warm wind, the west wind, full of birds' cries;

I never hear the west wind but tears are in my eyes.

For it comes from the west lands, the old brown hills,

And April's in the west wind, and daffodils.

Not this year, it wasn't. John Masefield's warm westerlies hardly showed up last month, nor have they put in an appearance so far in May. Indeed, the poet would also have remained unusually dry-eyed in March, February, January, December, November - and so on, right back to, and including, last April.

For the westerlies - as defining, and important, to Britain as the monsoons are to India - have virtually vanished over the past 13 months. There has, according to leading meteorologists, been nothing quite like it for at least 30 years.

"The prevailing west-south-west has not been prevailing for the last year," the Meteorological Office said ruefully last week.

Weathermen say that the strange disappearance of the westerlies explains the weird phenomena of the past year - including last summer's heatwave, the long drought, the biting winter, this chilly spring, and the unusually fine blossom of the past weeks. They even claim that it should take the blame for forecasters getting it wrong so frequently.

North and north-easterly winds have dominated the year instead of the westerlies. They brought snow to the Surrey stockbroker belt on Thursday. They have caused frost warnings almost every night so far this month. And they blighted the Bank Holiday, causing a 10 per cent rise in air travel to warmer climes and freeing the roads from most of their traditional congestion.

They have also been behind what the Institute of Hydrology last week called "an extremely intense drought". The 12 months to April, it says, were the fifth driest in the 228 years for which records have been kept. Only two months - September and February - produced above-average rainfall: in a few districts in northern England every single month has been unusually dry.

So far, May has been one of the driest months on record - one site, in Essex, has recorded only 1 per cent of average rainfall. Reservoirs are low in five of the 10 water company areas, with Yorkshire, the North- west and the South-west particularly badly hit. With warmer weather expected before long, increasing evaporation, there is little chance of stores replenishing and a great one of further restrictions.

Meteorologists have no difficulty in explaining how the westerlies have failed, but they have no idea of why. It has happened through a reversal of normal weather patterns.

Usually, low pressure dominates the area near Iceland and there is a big area of high pressure near the Azores. This combination, which has been particularly strong over the past 10 years, propels the westerlies across Britain. For the past 13 months, however, this pattern has been upside down, with high pressure to the north-west of us and low pressure to the south-west.

This has drawn down north and north-east winds over Britain: this month, for example, they have been coming across the still-cold North Sea. And they have been dry. The fronts bearing rain have been passing to the north of us to hit Scandinavia, or to the south to bring unusually wet weather to Spain, Portugal and Morocco. And the weather seems to have set into this pattern, blocked into position by the stable cyclone and anti-cyclone.

"If you get a high pressure and a low pressure in a certain position, the pattern becomes blocked like this, and it can be very, very difficult to move away from it," says the Met Office. "That is what is happening at the moment and has been now for many months. Every time a block has broken down, this has only been temporary. There has been an unsettled spell for a week or two, and then the block appears again."

David Parker, a climate research scientist at the Met Office, cannot remember so long a period of north and north-easterly winds for nearly 30 years. The last time it persisted for a whole year was in 1968-9, Dr Parker says, although there were shorter periods in the Eighties.

Philip Jones, of the climate research unit at the University of East Anglia, says that the pattern has played havoc with predictions. "Most weather forecasting for two weeks or so ahead breaks down when a situation like this occurs," Dr Jones says.

The computer models used by the forecasters are "always trying to set up the prevailing westerly situation" and can never tell how long the block is going to continue. "Nobody can say when this pattern is going to end, or why it is happening," Dr Jones says.

Terry Marsh, who runs the national hydrological monitoring programme at the Institute of Hydrology, says that he personally feels that the unusual weather is connected with global warming and that the water industry, in particular, should take this into account. And last week, James Oatridge, director of environmental and corporate controls at Severn Trent plc, said that the industry was having to "face up" to climate changes, and to the possibility that droughts "might become a more frequent occurrence in future decades".

However, Dr Jones says that computer models predict that global warming would instead have the opposite effect to the present weather pattern, and would actually strengthen thewesterlies.

Whatever the cause, the unusual weather is having a strange effect on nature. Daffodils and bluebells have been late in appearing and frogs have been tardy in mating. And it seems to have been a remarkably good year for blossoms.

English Nature, the Government's official wildlife watchdog, thinks that last year's good summer may have set trees up to blossom well, while the recent cold weather has preserved the blooms.

And it adds that the late spring may have "telescoped" the usual process so that different trees, which would otherwise have staggered their flowering, have all blossomed at the same time, magnifying their impact.

Meanwhile, says the Met Office, westerly winds are predicted for tomorrow, but it will not hazard a guess as to how long they will last.