15 Oct 2012

The Great Storm of 1987 – how forecasting has improved since then

The Great Storm of 1987 left a swathe of death and destruction across southern and eastern parts of England. Although forecasts in preceding days mentioned that very windy weather was expected, they failed to capture the severity of what occurred.

Whilst the government praised the authorities and emergency services for their efforts in helping those affected by the storm, weather forecasters faced questions as to why the severity of the storm had been underestimated.

Following the storm, an internal Met Office enquiry was carried out, scrutinised by two independent assessors which identified changes that should be made to improve forecasts.

Weather chart at 6am on 16th October 1987 – courtesy of the Met Office

What went wrong with the storm?

Whilst weather computer models had been suggesting very windy weather in the days before the storm hit, the general thinking was that the zone of damaging winds would stay over the English Channel and northern France.

However, as can happen with rapidly developing storms, the forecast can change slightly at relatively short notice – mainly because of small details that have been badly assimilated by the weather computer models. Despite being small details, they can end up having a sizeable effect on the outcome.

Why did forecasters underestimate the severity of the storm?

The storm developed quickly over the Bay of Biscay – an area where aside from satellite imagery, there were very few weather observations available.

This meant that whilst the low pressure was forming as expected, there was a lack of measurements of wind strength until it approached southern coastal parts of the UK.

In effect, although it was known that very windy weather was on the way, the fact that the winds were more severe than initially thought only became clear with very little notice.

Forecasting improvements since 1987

Since October 1987, a number of improvements have been made. Some came as a result of an enquiry after the storm and others because of developments in science and technology over time.

In the 1980s, the Met Office supercomputer was capable of 200 million calculations per second, increasing to 1 trillion per second by 1997.Today, the latest IBM computer crunches through a whopping 100 trillion calculations every second.

This continuing increase in computing power over time has allowed the weather models to not only become more detailed (higher resolution) but to be run more frequently.

In October 1987, the detailed forecast that focused on the UK ran just twice a day. Today it is run four times a day and at a much higher resolution, allowing more local detail to feature in forecasts.

The number of weather observations at sea to the south and west of the UK has also improved significantly during the last few decades. There are now automated floating buoys that are able to feed a variety of weather information into the network – ensuring that forecasters get a feel for a storm before it reaches land.

As well as an improvement in observations at the surface, satellite imagery has also become much better than it was 25 years ago.

Not only is satellite imagery more detailed and of greater frequency, it can also be assimilated into weather computer models as a source of information.

This allows the weather computer models to get a better sense of the state of the atmosphere from which it can build on to get a more accurate forecast.

Better warnings and communication

There is no doubt that over the past 25 years the communication of weather has improved immensely.

This has partially been achieved by developments in computer graphics which give weather presenters the tools to tell the weather story in a better way, but also by an improved severe weather warnings system.

Post October 1987, the warnings system was overhauled to focus on tiered warnings that were linked to the severity of the weather expected, as well as making the potential impacts clear to the public as well as authorities.

During the nine years that I’ve been presenting the weather, I’ve noticed a huge change in how people consume weather information.

Previously TV and radio were the most popular choice, but in an age of computers and smart phones, the thirst for weather information is increasingly satisfied by websites, apps and social media.

How has accuracy improved?

Improvements in science and greater computing power have led to significantly more accurate forecasts.

Whilst the forecast still goes a little wrong on occasions, today, a Met Office four-day forecast is as accurate as a one-day forecast was three decades ago.

Given how rapidly computing power increases and constant developments in the understanding of our atmosphere, it will be interesting to see how much forecasts will have improved in another 30 years.

If you have any memories or pictures of the Great Storm of 1987, I’d love to hear from you. The easiest way to get in touch with me is on Twitter – @liamdutton

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