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Why does Frontal Snow mostly occur in the same few geographical locations?

  • 28-01-2021 2:57pm
    #1
    Banned (with Prison Access) Posts: 2,254 ✭✭✭ Nqp15hhu


    If we look at recent or prior events, where a warm front will head north, frontal snow usually occurs in South Ulster.

    From memory we usually have at least two or three of these “events” each winter.

    I have identified three different types of events:
    - A warm front moves into cold air, stalls and is pushed south by the colder air. Usually this stall occurs over south Ulster. Precipitation is usually orientated on a NW to SE orientation, so snow will reach as far north as Letterkenny (at times) in the west but will be dry in Derry and Belfast. For example, the frontal system last week that brought snow to letterkenny brought clear skies to my location.
    - A warm front moves into cold air and pushes across the island, only to stall further ahead. This usually occurs in a system that moves from SW to NE and the stall usually occurs over SW or South central Scotland. With the snow being around that general geographical area.
    - A slider low. This usually occurs over the south of Ireland, moving from Galway south across to Wexford.

    I can only think of one recent event where the stall occurred over Northern Ulster.

    18th January 2013: https://www.metcheck.com/WEATHER/gfs_reanalysis_1871_now.asp

    Produced about a foot of snow here on the hills above 200 metres. The low was orientated on a NW to SE orientation so was more of a slider low.

    Looking ahead we have a front coming through on Saturday morning. Initially this was supposed to be snow over me, but has trended south over time and is now probably going to be over South Ulster. Again.

    The same general pattern reoccurring over time. With rare frontal snow in North Ulster. I would love to know why this occurs time and time again.

    Is it something to do with the jet-stream’s orientation? Something to do with the influence of cold air in Scotland??


Comments

  • Moderators, Science, Health & Environment Moderators Posts: 15,178 Mod ✭✭✭✭ Gonzo


    In short, there is nowhere better positioned for cold weather and snow than Scotland when you look at the British Isles. They are further north than Ireland, Northern Ireland, England and Wales.

    They have the advantage of being part of a significantly larger landmass compared to Ireland. Apart from being further north, they are also further east which also helps. Much of Scotland is mountainous so that's another advantage.

    If you look at the UK mainland most of it is more prone to frontal snow than Ireland due to it's positioning, it's more sheltered from the Atlantic, it has a bigger land area and has the cold continent directly to the south with little sea modification when it comes to southerly winds. Southerly winds can be cold for them in the winter if the continent is also cold, but for us they will always be mild as we have a large areas of sea/ocean to our north, west and south.

    This also helps them massively in the summer. Southerly winds can bring plumes of heat up from France and Spain directly into England, but the same southerly winds will be off a cool sea for us.

    As for Northern Ireland, it's not much different than the republic, it may be further north, but it is more influenced by the warm Atlantic than any other part of the UK with the exception of maybe south-west England and Wales. It is further south than Scotland and further west so generally has the same difficulty in getting snow just like much of the republic. Northern Ireland does come out better with northerlies of course when they are cold enough as north facing coasts make up the majority of the NI coastline and snow showers can get as far south as County Down if conditions are right. Just like easterlies, the northerlies have to be properly cold to bring snow to low levels including coastal areas with as little Atlantic modification as possible.


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