Heavy and thundery rain across Ireland and the UK

  • Thunder and lightning near the iconic London Eye (Photo courtesy of Lewis Whyld/PA Wire/Press Association Images).

    A radar image of Ireland from Friday, 27th June showing the distribution of showers across the country (screenshot from raintoday.co.uk).

    Another screenshot of the heavy, thundery rain moving up from the south towards the UK (screenshot from raintoday.co.uk).

    A shot of a Mesoscale Convective System developing in south-west Francce (photo courtesy of the MeteoEarth weather app).

  • Heavy and thundery rain across Ireland and the UK
    27.07.2013 13:42

    Following the recent hot and sunny weather across the UK, the weather has taken a dramatic turn as widespread showers and thunderstorms developed over many areas.

    The high pressure that brought the settled weather last week has drifted towards Scandinavia, losing its influence on the UK’s weather. Low pressure systems then moved in with showers and longer spells of rain across many areas. Across Ireland, heavy and thundery showers brought flash flooding to many places. Numerous reports of funnel clouds (cone shaped clouds that reach towards the ground from the base of a cloud-usually associated with tornadoes) were sighted with one reported small tornado on Friday, 26th July in the west of Ireland. Figure 2 from the MeteoGroup radar (www.raintoday.co.uk) show the distribution of showers across Ireland on Friday the 26th where scattered heavy showers brought locally torrential downpours to many places.

    Across Scotland, the showers tended to merge into longer spells of heavy rain. Much of England and Wales experienced thundery activity at the start of the week but it tended to stay largely dry from midweek onwards.

    The Spanish Plume and its possible impact on the UK

    As the week progressed, computer model output seemed to suggest that a plume of warm air, derived from eastern Spain, would move towards northern France that brought some locally heavy rainfall. This air derived from more southern latitudes and is commonly known as a Spanish Plume. Spanish Plumes form when a ‘plume’ of very warm air ahead of cooler air moves towards north-west Europe bringing heavy and thundery showers to many places.
    As the plume reaches north-west Europe, the atmosphere becomes unstable with the warm air in mid-levels of the atmosphere. As the cooler air from the cold front overruns the warm air, instability causes vigorous convection within the plume which then causes a series of organised thunderstorms to develop. If there is significant wind shear (i.e. a change of wind direction with height) then hail, gusty winds and even tornadic storms are possible. Figure 3 from 13:30 on Saturday the 27th, shows the thunderstorms associated with this plume edging into southern England bringing frequent lightning strikes and locally heavy rainfall.

    The week ahead…

    The forecast for the next few days looks fairly unsettled across the UK as rain edges north into northern England and Scotland over the rest of this weekend. A low pressure system in the Atlantic is expected to bring further heavy showers and longer spells of rain to many areas towards the start of the week that may bring further thundery conditions, particularly in northern and western areas. South-eastern England is likely to have the best of the warm, sunny weather.

    Elsewhere in Europe

    The Spanish Plume that spread into northern France helped develop a Mesoscale Convective System (a group of thunderstorms organised in a system on the scale of around 100km; as shown in the MetoeEarth weather app; Figure 4). This system moved into northern France bringing some locally torrential rain and frequent lightning, as well as gusty winds. In fact, as the storms evolved through Friday evening, a gust of 102mph was recorded at Pauillac, western France. The storms continues to move in the Benelux countries and north-west Germany on Saturday. In eastern parts of Germany and Central Europe though, it will be exceptionally hot with temperatures expected to get into the mid to high thirties.

    By: Seán Penston