The water evaporates from the land and ocean, condenses, falls back to earth as precipitation, and the water that descends over land either returns to the air by evaporation or plant transpiration, or it flows back to sea via streams and rivers. This movement is called the water cycle.

Today we know the amounts of water at each stage in the cycle and that, on average, a water molecule spends 9-10 days in the air between the time it evaporates and its return to the surface. Of all the water on Earth, only about 0.35 percent is in the air at any time, yet it is this small amount which brings us all our clouds, fog, rain, snow and hail. If precipitation were distributed evenly, every place on Earth would receive 857 mm (33 and three quarter in) a year. In fact, about 77 percent of all precipitation falls over the sea. The rest descends over land, but some places receive much more than others, water is often scarce in many parts of the world, such as deserts.Next Week......Water and WeatherThe answer to last week's question: 100-200 mph.This week's question: How much precipitation falls over the sea:A/ 66%.B/ 77%.Good Luck.Glossary: Angular Momentum: The energy of motion of a spinning body or mass of air or water. Its value depends on the mass of the body, its radius spin, and its rate of spin.Weather for coming week Monday 28th January-Friday 1st February.High pressure early on replaced by a large low pressure system as the week moves on.Monday into Tuesday dry and mild, then light rain later Tuesday with increasing winds.

Wednesday sunshine and squally hefty showers after early frost in parts.

Thursday some wind and rain.Friday colder with sunshine and showers, some wintry in places.Maximum temperature 6-10c 43-50f.Minimum temperature 1-6c 34-43f.Last Week's Observations (Monday-Sunday)Highest day temperature............14.0c 57f on Wednesday 23rd January.Lowest night temperature...........minus 0.3c 32f on Sunday 27th January. Wettest day..................................1.2 mm Monday 21st January.