Weather Watch

In the end it was another warm month, especially by day, with temperatures 1.5C (nearly 3F) above the norm.

It was reasonably sunny, and dry as well, with just one-third to a half the usual rainfall. It was the driest May for 12 years.

For most of us, the last May to be either wetter or cooler than average was in 1997.

The depression over the Continent, which gave a dismal spell with north-easterly winds at the end of April, was pushed away south-east by a ridge of high pressure. It became fine and quite sunny, with only one or two showers on the first bank holiday Monday.

But another low was already advancing south-east towards Britain. Its associated fronts brought rain.

The depression settled over the country. It deepened remarkably for the time of year, more typical of autumn and winter, giving the lowest pressure for May in my logs by a large margin. It generated plenty of showers over the next three days, though these were well scattered over our region, with just the odd rumble of thunder and a little hail.

As the low withdrew across northern Europe, it again pulled down the north to north-easterlies that tend to plague us so much in the spring. This year has been no exception, and we were to endure a further week of them. The weekend was particularly miserable: misty, murky and drizzly - but it did pose an intriguing puzzle.

Where was the "hot spot" in the British Isles? With the breeze from the north-east, I would have guessed somewhere on the south coast, far away from the North Sea.

It was warm down there, about 17-18C (mid-60s F), but the answer was the Shetland Isles, the far northern tip too, at Baltasound. It reached 19C (66F) there, while we struggled to get to 10C (50F).

The situation was characteristic of the rare occasions when the Shetlands can be warmer than most of Britain. It was similar when Sumburgh, on the southern extremity, achieved the hottest ever temperature recorded on the islands, 27.8C (82F) in August 1910.

With a depression over northern Europe and winds circulating anti-clockwise around it, as ever in the Northern Hemisphere, hot air was drawn north over eastern Europe and then west across Scandinavia.

Here, it crossed the mountains and on descending, the airstream dried out and warmed up further due to the Fohn effect. With a relatively short sea crossing to Shetland, the airstream remained cloud-free and did not cool much.

So with essentially the same airmass affecting the North-East of England, why was there such a contrast in the weather?

In the first place, with the breeze coming to us via the southern Baltic and Denmark, there was no mountain range to help dry it out. In addition, the much longer sea track enabled it to pick-up plenty more moisture, producing those leaden skies, and reduced its temperature close to that of the North Sea, which, off our shores, is hardly any warmer than the Atlantic around the Shetlands.

Here, for our hottest days in summer, we look for a southerly drift from France via central Britain. The nearer you are to the coast, the more brisk it should be, to keep those chilly sea-breezes at bay.

After the dull spell, things slowly cheered up. Pressure rose slowly and steadily. By the 16th, an anticyclone was sitting in the South-West Approaches. A westerly flow became established and, with plenty of sunshine, the highest temperatures of the year were measured.

Weak fronts introduced cloudier conditions, then a more active trough took some patchy, heavy rain south-west across our area as winds again turned north. It brightened up, but clear skies led to a widespread ground frost, even a late air frost in those localities prone to it.

Another fine, sunny weekend followed and the mostly dry weather persisted during the next week as the high re-asserted itself over western districts, though it was more cloudy at times. Despite the breeze blowing from a northerly quarter still, daytime temperatures weren't far from typical values for the time of year, though there were a few more ground frosts at night.

Towards the end of the last week, the high transferred towards Scandinavia. This allowed Atlantic frontal systems to move in from the south-west. These brought a lot of cloud but mainly just sprinkles of rain.

The spring was mild, around 1C(2F) above what we'd expect. Only that of 2001 has been on the cool side in the last eight years. It was quite dry in the west of our region but fairly wet in the east, largely because of the drenching in mid-April.

MAY TEMPERATURES & RAINFALL at CARLTON IN CLEVELAND

Mean max 6C, 61F (+1C, +1.8F)

Mean min 6.4 C, 43.5F (-0.1 C, -0.2F)

Highest max 22.3C, 72F, 16th

Lowest min 0.4C, 33F, 22nd

Total rainfall 20mm, 0.8ins (-22, -0.9ins)

Wettest day 8mm, 0.3ins, 20th

No of rain days with 0.2mm (0.01ins) or more: 7 (-6).

(Figures in brackets show difference from 21-year mean, 1984-2004)