In August and September 2008 there were major floods in parts of the UK when exceptionally large amounts of rain fell in very short periods. We have looked back at what happened, meteorologically, and also at our own forecasts and warnings during both periods.
Our findings highlight that for 15-16 August and 5-7 September we issued accurate forecasts and timely warnings of severe rainfall. Working closely with the Environment Agency, which has responsibility for hydrological forecasts, we kept emergency responders informed throughout both events.
The Met Office's short-range ensemble prediction system, known as MOGREPS, provided exceptionally good guidance of both the amounts of rain and the location of the area most at risk during the September event. MOGREPS is designed to provide risk assessment and uncertainty information for the short-range forecast in the first two days, with particular interest in severe, high-impact weather.
As well as predicting high probabilities of heavy rain in south-west England and south Wales, it later pinpointed the area just inland of the coast in north-east England and south-west Scotland, close to Morpeth, as having the highest chance of significant rainfall, more than 20 mm in six hours.
August
On 16 August prolonged heavy rainfall led to many areas in Northern Ireland being flooded.
| Met Office forecast timeline - August 2008 | ||
|---|---|---|
 |
Advisories of a moderate risk of a severe weather event on Saturday 16 August, issued via our website | |
| 15 August | Advisories upgraded to early warning of severe weather, with up to 60 mm of rain in places | |
| 16 August, 3 a.m. | Flash warnings, including the risk of flooding, issued, valid until 6 p.m. | |
| 16 August, 5.30 p.m. | Flash warning extended to 10 p.m. for County Antrim and County Down | |
Weather conditions
 |
| Surface synoptic analysis, Saturday 16 August at 1200 UTC |
The start of August had been very wet. In the week preceding the heavy rainfall of 16 August parts of Northern Ireland, and Scotland, had localised flooding. Some areas in Northern Ireland recorded their monthly rainfall averages – around 70 to 80 mm or three inches - between the 11th and 15th.
Surface flooding had already resulted in road closures during the 12th. Further heavy and locally thundery downpours occurred on nearly every day during the week of the 11th-15th.
This had all resulted in the ground being saturated and river levels being high.
On 16 August a slow-moving frontal system brought torrential rainfall as it north-east across Northern Ireland
Impacts
- More than two inches (55-65 mm) of rain fell widely across many central and eastern parts of Northern Ireland
- Highest official rainfall total was 74.8 mm (three inches) at Portglenone (Ballymena) in 12 hours - a one-in-90-year event. An unofficial rain gauge in Ballyclare Co. Antrim recorded a 24-hour total of 88.9 mm (three-and-a-half inches) - a one-in-150-year event
- Widespread disruption included 37 road closures, a train derailment and collapsed bridges
- A newly opened underpass in Belfast was completely filled with flood water – up to 15 feet deep at times
Met Office actions
- Warnings issued three days before the event
- On 15 August our Public Weather Service advisor in Northern Ireland held a teleconference with emergency planners and local authorities
- On the morning of 16 August relevant agencies informed by text message that there was significant risk of surface flooding in eastern parts of Northern Ireland during Saturday afternoon and evening
- Ongoing conferences held with Gold Command (emergency centre) during the event
- Media briefed
- Government departments were briefed
While the rainfall on 16 August was capable of causing surface flooding, close consultation with the Environment Agency alerted us to the fact that the problem would be greatly exacerbated by the pre-existing state of the ground and high river levels created by heavy rain throughout the previous days.
September
Heavy rainfall between 5 and 7 September resulted in many parts of England and Wales being flooded.
| Met Office forecast timeline - September 2008 | ||
|---|---|---|
 Figure 1: Radar image 12:00 5 September |
31 August | First indication in medium-range guidance of large rainfall totals on Friday 5 September, focused on SW England and Wales |
| 2 September | Advisory for heavy rain for SW England, Wales and central southern England issued via website | |
| 3 September | Early Warning for heavy rain on Friday in SW England, Wales and parts of central southern England issued to public and relevant agencies. Advisory for heavy rain for NE England issued via website | |
| 4 September | Early Warning for heavy rain updated with 80% risk of disruption to south-western parts of the UK, issued to agencies in south Wales. Early Warning issued for NE England for Saturday. Advisories issued for other areas, including advisories eastern parts of Northern Ireland and parts of southern Scotland. Totals expected to exceed 50 mm (two inches) in places. | |
| 4 September (p.m.) | Early warning for SW UK upgraded to Flash warning and extended to other areas. | |
| 6 September | Flash warnings issued for more than 60 mm in part of the UK, across the high risk areas during the day. | |
Weather conditions
 |
| Surface synoptic analysis, Friday 6 September at 1200 UTC |
An area of low pressure that moved north-eastwards across the UK on 5 and 6 September brought prolonged heavy rainfall to many areas, especially south-west England, Wales, south-west Midlands and north-east England. The event was in two clear phases. The early phase was from a combination of frontal and convective rainfall, which affected Wales and part of south-west England on Friday. The second phase took place on Saturday/early Sunday over Northumberland due to very prolonged heavy frontal rainfall, driven in on a strong north-easterly wind.
Impacts
- Widespread disruption and more than 1,000 homes damaged - particularly in south Wales and Northumberland
- River Wansbeck burst its banks, flooding Morpeth
- Train services in Wales disrupted because of a landslip
- Liscombe, Somerset recorded 74.6 mm (almost three inches) in 24 hours on 5 September, more than a month's rainfall
- Albemarle, Northumberland recorded 112.0 mm (four-and-a-half inches) in the 72 hours from 09:00, 4 September to 09:00, 6 September, most falling in 48 hours
Met Office actions
- Our Public Weather Service advisors were in attendance or contact with Gold Commands in Gloucester, Wales and Northern Ireland
- Formal conferences held between our Chief Forecaster, our emergency response team and the Environment Agency
- Press Release issued
- Liaison between Met Office and Environment Agency press teams and the media continually briefed.
- Government departments were briefed
