The storms of October 2000

A major cyclogenesis (i.e. formation of a depression) took place on 26 October in the north-western part of the Atlantic Ocean - the result was a deep low pressure, anchored between Greenland and Iceland, and, over the next two days, an extensive cold front built up, stretching its way well towards the south-west. This became the 'birthplace' for the first in a series of highly potent wave depressions that tracked across the UK between 28 and 30 October.

The 'parent' low and its trailing cold front are clearly seen on the Atlantic infrared satellite image for 0600 UTC on 27 October (Fig. 1). Over the following few days, three 'daughter' depressions swept across the UK, bringing heavy rain, strong winds and further flooding in addition to extreme weather events such as tornadoes.

Figure 1. Infrared satellite image for 0600 UTC, 27 October

Figure 2. Radar image for 0700 UTC, 28 October

The first of the daughter depressions deepened quickly as it crossed the country during 28 October. It brought a milder 'tropical maritime' air mass, so, for a while, the passage of the warm front was accompanied by a period of heavy rain in many places, with up to 8 mm being reported in an hour across parts of the Home Counties. This rainfall can be seen on the radar image for 0700 UTC (Fig. 2).

During the afternoon, the cold front swept eastwards across Wales and England, accompanied by gale force winds as the depression continued to deepen. A tornado was reported in Bognor Regis shortly before 1700, resulting in local severe damage.

Later in the day, the centre of the depression turned towards northern Scotland and brought a spell of gale force winds to much of the north during the following 12 to 24 hours. The cold front had, by now, swept into the North Sea, so, clearer, chilly conditions prevailed across most of the UK overnight and into the first part of 29 October.

The visible satellite image for 1200 UTC (Fig. 3) shows most of the country still in the reasonably fair weather, although the dappled pattern of clouds indicates showers over some northern areas. Towards the south-west, a large bank of cloud can be seen, with the second depression forming over Eire and the third depression forming near 52° N, 30° W.

The veil of upper cloud ahead of the second storm spread very quickly north-east across Wales and all but the far north of England by mid-afternoon on 29 October. Rain set in soon afterwards, becoming steadily heavier and more persistent as dusk approached. By 1700, heavy rain had spread across much of the southern part of the country, accompanied by strong winds. Some of the strongest gusts were experienced across Wales and south-west England, e.g. 76 knots (87 m.p.h.) at North Hessary Tor on Dartmoor.

Rain continued to fall across southern areas during the early hours of 30 October and, during the second half of the night, the new and rapidly deepening depression crossed Ireland, the Irish Sea, Wales and then on into southern parts of northern England. The steep pressure gradient resulted in strong winds and widespread gusts of between 70 and 90 m.p.h.

As is most often the case, the strongest winds were experienced to the south of the centre of the depression, while most of Scotland, Northern Ireland and parts of northern England escaped with much calmer conditions. Wind speeds reached a peak in the early hours along the South Wales coast, touching 84 knots (96 m.p.h.) at Mumbles.

During the following few hours, the strongest winds transferred east, with the Isle of Portland in Dorset reporting a gust to 81 knots (93 m.p.h.) at 0600. The strongest winds accompanied the passage of the cold front that passed through London between 0600 and 0700, and cleared into the North Sea by around 0800. Langdon Bay near Dover registered a gust of 76 knots (87 m.p.h.) between 0600 and 0700, and, by 1000, this weather station had been reporting gusts to 60 knots (69 m.p.h.) or more for 16 hours. At inland locations, typical gust strengths were 50-70 knots (57-80 m.p.h.). Some structural damage accompanied these gusts, with trees brought down and roads and railway lines blocked.

Rain had fallen all night, so, by 0900, 24-hour totals of between 25 and 50 mm were commonplace, with locally 75 mm and more. Local flooding occurred and caused major disruption to commuters during the morning rush hour of 30 October. In a number of areas, the cumulative effect of these heavy storms brought the situation close to breaking point, and the heavy rain on 30 October resulted in much more serious flooding problems, in areas as far apart as Kent, Wales and Yorkshire.

Figure 4. Radar image for 0900 UTC, 30 October

Another area of severe weather developed as the depression crossed northern England and the pressure at its centre continued to fall. The warm and cold fronts formed a sharp apex, in between which was located a narrow band of warmer air from further south. Temperatures at some locations rose some 5-7 °C within the hour. But as the cold front crossed, the temperature fell dramatically.

The depression had by now developed a wrap-around of thick cloud, and heavy precipitation occurred to the west and north-west of the centre, as seen on the 0900 UTC radar image (Fig. 4). However, the precipitation, falling into the already chilly air, turned first to sleet and then to snow, and swept eastwards just to the west of the retreating depression. Locally, the temperature was observed to fall as much as 10 °C within one hour, and a short spell of quite heavy sleet and snow set in. Several roads were badly affected, notably those across the Pennines.

During the morning, the depression moved out into the North Sea, deepening even further, and, during the afternoon, storm-force winds were recorded over the North Sea, with some in excess of hurricane force. Later in the day, the storm finally began to lessen in intensity as it neared the south of Norway.

next: The passage of a depression - the example of 30 October storm