IT was almost inevitable that after two record-breaking months, the weather would return to nearer the norm. However, with a final fling during the last week, May too, overall, became quite sunny and mild. With our area faring better than most of Britain, it was the warmest May for four years, the sixth consecutive one to be warmer than usual. It was generally only slightly on the wet side.

Temperatures were consistently average until the last week. Then, as the wind backed into the south, summer arrived early. Although it became considerably warmer and more humid, the mercury marginally failed to reach the heights achieved in mid-April.

Whereas in the previous two months the accent was on warmth during the day, in May it was the nights that were particularly mild due to the cloudier skies and stronger breezes. There was a lone, widespread, ground frost early on the 15th, as the wind died down and skies cleared following a brief incursion of cool north-westerlies.

It may have been cloudier than in March and April, when amazingly we had double the ration of sunshine, but it was still sunnier than normal.

Not surprisingly, spring was very sunny and the warmest in my 20 years of data here at Carlton, near Stokesley, with the mean maximum being an incredible 1C (2F) above the previous highest. The lack of northerlies, usually most common in spring, helped here. Also, there was one solitary day with sleet falling. The lowest number with sleet or snow in any spring before was six, last year.

The changeable spell that became established during the last week of April continued throughout May. Several depressions, one after another, often fairly deep, tracked north-east. Consequently, winds were mostly from the south-west and frequently brisk.

Frontal systems brought longer periods of rain, but since the parent lows tended to be slow-moving, there were gaps of several days between them. In the shelter to the east of the Pennines, they produced only modest rainfall. An exception was on the 2nd when a depression crossed our region, giving a wet, miserable day, the first like it since February.

Between the fronts, there were a couple of dry interludes, from the 5th to the 9th and again during the final week, when high pressure nudged closer to the South-East. Otherwise, with the lows relatively close, there was an abundance of showers. They tend to develop vigorously over the land anyway at this time of year due to the buoyant thermals created by the sun as it nears the peak of its strength.

Indeed, some were torrential, with hail and a few rumbles of thunder. Sleet fell on the 10th, though mainly on the higher hills. On the 13th, several places, including here at Carlton, experienced marble-sized hail. Even this size is quite scary if you're out in such a shower, so imagine what it is like when grapefruit-sized hail hurtles down. Many people are killed around the world by missiles of this calibre, especially in central China.

With lots of sunshine between the showers, there were plenty of opportunities to see rainbows. These form as the light from a point source, like the sun, passes through raindrops. These act like tiny prisms and refract the light, splitting it into the familiar colours. Reflections from other drops then shape the arc, which is displayed on a "screen" of rain further behind.

Rainbows vary greatly according to conditions at the time, providing a wealth of different effects. The lower the sun is in the sky, the higher is the arc of the bow, so that they are at their most spectacular at sunset. However, around the middle of the day in late spring and summer, you cannot see a rainbow unless you are standing on a hill and looking down. From an aeroplane you might be lucky enough to observe a complete ring.

The larger the raindrops, the brighter are the bows. Very fine droplets give a virtually white arc, as may rarely be seen in fog. Additional, paler bows may be present just inside the primary one, either merged with it or slightly detached from it. A "secondary" bow sometimes appears with a much larger diameter, with the colours reversed, but more feint. At night, the moon can produce pale, usually colourless arcs.

MAY TEMPERATURES

& RAINFALL

at CARLTON IN CLEVELAND

Mean max. - 16C, 61F (+1C, +1.8F)

Mean min. - 7.9C, 46F (+1.4C, +2.5F)

Highest max. - 24.7C, 76.5F, 31st

Lowest min. - 0.7C, 33.5F, 15th

Total rainfall. - 53mm, 2.1ins (+9mm, +0.35ins)

Wettest day. - 7mm, 0.3ins 19th, 20th

No of rain days, with 0.2mm (0.01ins) or more. - 17 (+4)

(Figures in brackets show the difference from the 20-year mean, 1984-2003)