Turning Stormy? The weather across the UK and Ireland is set to become increasingly unsettled over the next few weeks as the north Atlantic jet-stream strengthens. A severe cold spell is forecast to affect north-eastern United States which will create a sharp thermal gradient across the north Atlantic generating an extremely intense jet-stream core. Current weather forecast models are predicting the jet-stream to reach speeds approaching 250mph by this Friday. Of course these winds will not be experienced at the surface but at a height of around 30,000 feet, meaning there will be a very strong tail-wind for eastbound transatlantic flights this week. A series of low pressure systems will develop across the North Atlantic this week in association with the strong jet-stream and will track rapidly east. The first major storm will track to the south of Iceland on Wednesday with its associated weather fronts bringing wet and windy weather to the Island, with the strongest winds affecting northern areas (Scotland). Weather forecast models suggest a brief respite on Thursday but there is increasing suggestion for it to become rather stormy across the UK from Friday and through next weekend. There is still great uncertainty with regards to the track and intensity of the storm systems but it is likely that northern areas of the UK will be at highest risk of seeing storm force winds. The upcoming unsettled weather marks a return to a similar weather pattern that dominated during the winter of 2013/2014 when a series of rapidly developing low pressure systems lashed the UK and Ireland. Last winter was the stormiest winter in over 20 years with a total of 12 major extra-tropical storm systems hitting the UK and Ireland. It was also the wettest winter since records began in England and Wales. Ensemble forecasting of Atlantic Storms Accurate forecasting of Atlantic storm intensity and track can prove very difficult, especially when the most dangerous field of winds is generally relatively small in size. A small deviation in track and intensity can lead to the severest winds moving to the north or south of the UK In order to correctly predict the track and strength of these storms it is necessary to use more than just deterministic forecasting tools. Ensemble forecasting tools offer an invaluable resource in providing probabilistic forecast data on potential storm intensity and track. The major ensemble forecasting system used by weather forecasters is the ECMWF (European Centre for Medium-Range Weather Forecasts) ensemble system which provides 51 different forecasts run from similar initial conditions. So instead of just one forecast a forecaster now has 52 different forecast solutions and therefore 52 different forecast storm tracks and 52 different storm intensity forecasts. Forecasters then group the different solutions and can decide on the most likely track of a storm. In certain situations the main weather forecast (deterministic forecast) may repeatedly miss out on a developing storm system while a number of the ensemble forecasts show a storm system. This provides critical information to forecasters who have the ability to warn the public that there is a risk of a potential storm impacting the UK even though the main operational forecast may not show the system. Be sure to keep up to date with the forecast here at WW over the coming days!
Posted on: Mon, 05 Jan 2015 18:21:21 +0000