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WEATHER FORECASTING SERVICES


FEATURE SPONSOR


THUNDERSTORM WARNING FOR WIND TURBINE OPERATIONS Bad weather is a significant cause of


installation and maintenance delays to both on and off shore windfarms. Whilst no one can prevent the arrival of a thunderstorm, early warning of its development and location ensures that key personnel are prepared for the possibility of a quick change to their activities


PRIORITY DECISIONS


Since overhead lightning means an end to ground activities, early warnings allow weather-sensitive tasks to be prioritised ahead of the approaching storm and all personnel and equipment kept safe. Equally as important for minimising downtime, thunderstorm warning systems which monitor the storm’s trajectory allow these activities to restart quickly after a storm passes.


HELICOPTER HAZARDS In addition to the disruption of ground operations, thunderstorms represent a real hazard for helicopters used to support offshore windfarms. It is not only the lightning which represents the danger, but the severe turbulence, wind shear, icing and damaging hail. Early detection and location of thunderstorms allows air traffic to be managed for the safety and comfort of those on board.


For example, thunderstorms are noted as a major cause of offshore helicopter accidents, as demonstrated by the Oil & Gas UK Health and Safety Report 2013 (for period 1992-2012): “For accidents caused by external factors, 86 per cent of them were because of weather related events, including five lightning strikes and an encounter with a water spout…”


WARNING SYSTEMS Thunderstorm warning systems can be either individual, stand-alone units positioned at the airport or helipad, or formed from a network of sensors spread out over hundreds of kilometres


40 www.windenergynetwork.co.uk


and operated by national weather services or private companies. Single site detectors have an advantage of being dedicated to the area around the site, so usually offer the greatest chance of detecting all local lightning activity compared to a third party network, which needs to reach a compromise between lightning detection efficiency and broad geographical coverage, especially for offshore sites.


Being located and owned by the customer, stand-alone detectors have no on-going data subscription costs, delays or reliance on internet access. Whilst regional networks typically provide greater individual lightning location accuracy, stand-alone sensors are designed to have sufficient accuracy to reliably identify which reporting zones around the site a thunderstorm occupies (distant, vicinity or overhead).


FORESEEING DANGERS


Whilst most thunderstorms drift into the user’s area of interest, some form directly over the site. If only lightning detection is used, the site will have no warning of this overhead threat until the first lightning flash occurs – which may


strike the site itself or nearby aircraft. With this in mind, UK-based meteorological instrumentation design company Biral recently developed a stand-alone thunderstorm warning system tailored for airport and helipad use, the BTD-300. An important feature of the BTD-300 is its unique ability to detect the presence of strong electric charge in the air or on falling raindrops, both of which can warn of the potential for overhead lightning activity before the first flash is produced.


Even if no lightning results, this warning is used to infer that a Cumulonimbus cloud is over the site. This is a significant weather event in its own right and one which is very difficult to detect by any other means during the night when no lightning is produced. Cumulonimbus clouds are a threat to all aircraft due to severe turbulence, wind shear and airframe icing. This warning greatly aids the duty Met Observer.


Dr Alec Bennett PhD MInstP FRMetS CMet Biral


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