Number of Storms This Season

On Monday the Daily Express reported a forecast by Accuweather which boldly predicted what we should expect for the number of storms this season.

Sadly it’s really not possible to forecast the number of storms the UK is likely to experience in any given winter season. The numbers that are out there in the media are really just speculation at best. Here is an analysis of a year’s worth of weather related headlines from that particular newspaper (done a few years ago but still relevant) which may be of interest.

Many official agencies issue broad brush seasonal forecasts and every year EuroTempest publishes summary assessments of these through the season starting from the beginning of November. So our next seasonal forecast is due out soon. Suffice to say that different agencies often contradict each other and even when there is consensus it’s generally in the very broadest and indefinite terms – e.g. an indication of a warmer winter than average being slightly more likely than a colder than average winter, and so on.

There is no official meteorological agency in the world that produces a seasonal UK windstorm forecast. Though rainfall is something that is forecast on a seasonal basis it’s again done in the very broadest terms and for example, a leaning towards the likelihood of above average rainfall for the season across the UK as whole doesn’t really say much useful about the likelihood of a significant flood event. As the Met Office put it; “the science, as yet, does not allow any outlook to provide specific detail on, for example, the number of nights of frost, days of rain or snow or the amounts of rain or snow we may see during the period,” and to that list of details can be added the number of storms that the Met Office is likely to name.

One challenge is that counting storm numbers really depends what you call a “storm”. We have seen other suggestions of up to 20 storms this season and, in fact, by some measures 20 storms may not actually be that unusual. EuroTempest issued wind alerts to our UK and Ireland clients for 18 different weather systems last season (Oct 2016 – Mar 2017 inclusive) which was actually a relatively quiet season in terms of impact. Only five of these weather systems were given names, though plenty also had yellow Met Office weather warnings associated with them. Also, the insurance impact of the majority of storms, named or otherwise, is generally relatively minor. For example, many of our alerts last season were green on our RAG scale, i.e. issued for awareness and reassurance that the coming system was unlikely to have a significant property/insurance impact – but significantly damaging systems were relatively rare, with only one storm (Doris) warranting a red alert from us.

Predicting the number of named storms is made even more complicated by the fact that whether or not a storm is named depends on more than just meteorological factors. Storms are now given a name when either Met Éireann (the Irish National Meteorological Agency) or the UK Met Office issue an amber wind warning. Amber wind warnings are issued on the basis of a forecaster’s assessment of the level of impact the wind is likely to have and the likelihood of that impact occurring. Though the meteorological agencies strive for consistency it is, to an extent, a subjective assessment. Furthermore, “impact” in this assessment is primarily about public safety and as such can vary with such (not necessarily strictly meteorological) factors as the time of day at which peak winds are expected. For example, if peak winds are expected at rush hour or on a weekend or Bank Holiday (when people may perhaps be more likely to be outside) potential “impact” may be assessed as being greater than if peak winds were expected in the middle of a weekday night and this may be enough to tip a yellow warning into an amber one. “Impact” as considered from a public safety point of view and “impact” from a property damage/insurance point of view are often quite different things.

There were five named storms last season, which was unusually quiet, and eleven in the previous season (the first season that UK Met Office or Met Éireann names were used), which in many ways was a fairly typical autumn/winter season. The Daily Express article suggested that there may be 10-13 named storms this coming season (11 in the headline) so effectively what they’re actually saying is that the coming season will be pretty normal.

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2017-10-25T10:20:49+00:00 October 25th, 2017|