Following Storm Ciara’s activity, the jet stream remains in a powerful state with high level upper atmospheric winds. Whilst this means that flight times from New York to London are likely to remain quicker than normal, it means that powerful low pressure systems are likely to spawn in the coming days.
That’s exactly what’s happening right now, actually, with several exceptionally deep areas of low pressure expected to form over the next 48 hours. Some, as deep as 920mb, may threaten minima pressure value records in the North Atlantic. These systems will begin to make inroads into the weekend, granted not at their strongest (or most deep), but certainly retaining enough power and moisture to produce some really quite disruptive weather across the UK.
Strong Winds
Wind gusts are likely to remain on the high side from Saturday (15th) through to Monday (17th), as Dennis will be quite slow to shift. Predicting exactly how powerful and where the strongest winds will occur is not possible at this stage, however it’s likely that much of the UK will be impacted with gusts of at least 50 to 60mph, however locally some places may experience 80 to 85mph, especially on coasts and hills. So whilst very strong winds are likely, more detail regarding which areas will experience the worst will be available nearer the storm.. i.e. tomorrow (Friday).
This following map (courtesy of Meteociel.fr) shows very strong (55-65mph) winds indicated by red colours throughout the UK on Saturday.
Heavy Rainfall
In many areas, river catchments are particularly saturated which means any additional rainfall will likely just flow downstream and become a potential flooding nuisance. Unfortunately, Dennis looks like being a big rainfall event to. The longevity of the system means that rainfall (where it falls) could really mount up. Most computer models suggest that between 2 and 4 inches of rainfall accumulation can be expected over the Welsh Hills, Pennines and hills of Western Scotland. However, much of England and Ireland, even to lower levels, could see between 1 and 2 inches of rainfall, resulting in a good risk of localized flooding elsewhere.
Met Office Warnings
Due to severe weather expected, the Met Office have issued a plethora of rainfall and wind warnings for the UK. Those associated with Storm Dennis last from Saturday through to Monday. Widespread yellow wind warnings have been issued for virtually the entire country, and yellow rainfall warnings have been issued for western and southern England and Wales. Amber warnings are now in force, for rainfall, for various areas. These include some southern Counties of England, and South Wales.
An Amber rainfall warning has also been issued for parts of North West England; Lancashire and parts of Cumbria. The heavy rain from Storm Ciara produced severe flooding in places here, expected to be potentially exacerbated by Dennis’s rainfall – orographically enhanced (meaning it is heavier on hills). This orographically enhanced “Hill rainfall” then enters river courses inundating lower levels.
Whatever you are doing this weekend, be safe. Storm Dennis looks like it could be a powerful system, producing some very difficult traveling conditions. Keep a close eye on Met Office warnings as these could be updated to include wider areas, especially the Amber warnings.