Snowy planes

Risky business of weather forecasting

28 March 2012

Weather forecasting is not just a hugely complex process — it's actually impossible to get it completely right all of the time, says Dee Cotgrove, Met Office Head of Communications.

It's not the case that science cannot predict what the atmosphere (and weather) is going to do next, it's rather that the atmosphere itself doesn't know what it is going to do next. Here in the UK, for example, we often see finely balanced situations where the weather could go in many different directions. Therefore all forecasters deal in risk - looking at the chances of many different outcomes happening and deciding which is the most likely.

The Met Office is regarded as one of the most accurate forecasters in the world and research shows our forecasts are right six days out of seven. It's because we're trusted to give the best possible guidance that government agencies, the UK's resilience community and businesses across a range of industries act on our advice.

We saw this in action during the first major snowfall of the winter across England on February 4-5 2012. Well in advance of the event, we gave guidance to the UK public and our customers and issued Severe Weather Warnings. Many people rely on our advice for everything from deciding whether to grit roads to stepping up operations at hospitals to deal with those affected by cold weather.

"We can only make these decision based on the risk as it's presented to us by the experts - the forecasters. In this case, the forecast was spot on - snow arrived exactly when the Met Office said it would."
A spokesman for BAA

Based on our forecasts for 10 cm of snow, planners at Heathrow moved a well planned operation into action - which included cancelling 30% of flights in advance. A spokesman for BAA said: "Heathrow runs at 99.2% of capacity with a plane taking off every 45 seconds, so treating the runway or sending out snow ploughs will immediately have an impact on flights.

"We can pre-empt issues by cancelling flights ahead of time to avoid passengers having wasted journeys and to keep operations running smoothly despite challenging weather conditions.

"We can only make these decision based on the risk as it's presented to us by the experts - the forecasters. In this case, the forecast was spot on - snow arrived exactly when the Met Office said it would."

In early December 2011 we issued a red Severe Weather Warning, the highest possible, as we forecast a powerful Atlantic storm would affect Scotland. Police and the resilience community there took a series of preventative decisions based on our forecast - including closing schools and vulnerable transport links.

A gust of 106 mph was recorded on the Tay Bridge, with Scotland's Deputy First Minister Nicola Sturgeon saying at the time: "The conditions are exactly as predicted when the Met Office issued its red warning."

Central Scotland Police Emergency Planning said Met Office forecasts and updates: "are vitally important to us and are a great source of detail for warning and informing our communities."

These are two examples of success stories in the daily challenge of dealing with risk. However, whenever dealing with risk rather than certainty, there will inevitably come a time when the most likely outcome does not happen. If schools are closed for a storm that does not materialise (say, it narrowly missed the UK), or flights are cancelled for snow that never arrives (say, it falls harmlessly over the Channel instead) there will inevitably be criticism.

But it's important to realise that if a forecast appears to be incorrect, it doesn't mean it wasn't the best guidance or that decision-makers were wrong to take action based on the advice. Our forecasts are right six days out of seven, so in the long-run relying on those forecasts is the best way to make decisions to minimise the impacts of the weather.

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