THE schoolwalk on Thursday was wet. My daughter was back in her winter shoes, her winter coat zipped up against the wintry weather.

As we scooted around the puddles, lime tree seed pods helicoptered about us, and I found myself playing my favourite September sport: trying to catch autumnal leaves, browning around the edges, as they spiralled down to earth.

It has been like that all week, but Thursday was special. Thursday was St Swithin's Day:

St Swithin's day if thou dost rain

For 40 days it will remain

St Swithin's day if thou be fair

For 40 days 'twill rain nae mair.

Swithin was a monk in Hampshire during the 800s. He was a trusted counsellor of King Egbert of the West Saxons, and he may even have built a cathedral at Winchester.

It is said that on his deathbed, he requested that he be buried outside where "the sweet rain of heaven" could tumble down upon him from the eaves of his own cathedral.

This came to pass, and Swithin was so content that he performed many miracles from beyond the grave. In fact, so many that the monks decided to dedicate a golden shrine to him inside the cathedral.

To complete the shrine, on July 15, 971, they moved his bones to pride of place within it. As the monk's ceremony began, a torrential storm broke outside and it rained for the next 40 days. This was Swithin crying in dismay at what had been done to him.

Hence St Swithin is the patron saint of drought relief, and hence the rhyming weather predictor which has been recited in this country since Elizabethan times.

Many European countries have similar saint-related rainy rhymes. In France it is St Medard's day on June 8 - St Medard is known as "le matre de la pluie" as when a sudden shower inundated his congregation he remained perfectly dry because an eagle had spread its wings over his head.

The Belgians regard rain on St Godelieve's Day of July 6 as the start of a wet spell, and the Germans fear inundation if it rains on the Day of the Seven Sleepers on July 27.

Which is all very wet and, of course, wildly inaccurate.

The cause of the daily schoolwalk drenching is the jet stream, a ribbon of wind shooting along 30,000ft up at a top speed of 315mph. It is formed where the cold air of the North Pole meets the warmer air of the tropics.

It was discovered during the Second World War. The Japanese were onto it first, using it to whizz gas-filled balloons laden with bombs over to north-west America.

British pilots flying between the US and the UK noticed that their return journeys were invariably quicker. Transatlantic jets today use the high altitude winds to save time and fuel.

Usually the jet stream blasts straight over the top of Britain, keeping all the nasty wet weather to the north of us. This year, it has sunk slightly south, allowing depression after depression to drench us on the walk to school.

But look to the sky to see if the jet stream is returning and summer is arriving. Because if, in July, there is enough blue in the north-west skies to make a pair of Dutchman's breeches, fine weather is on its way.

And look to the ground for a longer-term forecast. Because, as everyone knows, if the ant hills are high in July, winter will be snowy.