An area of low pressure is forecast to develop somewhere between Scotland and Iceland later on Sunday and rapidly deepen into a deep depression as it moves to the north of Scotland on Monday morning. The numerical weather models having been simulating the development of this low for a number of days now, but the exact track of this low can’t be nailed for sure this far out.
This morning, the American GFS model has the centre of the low and tightest isobars/strong winds closest to mainland northern Scotland, whilst the European models (UKMO and ECM) have the centre of the low further north to the north of the Northern Isles. Suffice to say, all three solutions bring the risk of severe gales to parts of Scotland later on Sunday and through Monday. The chart below from the 00z GFS run shows winds gusting to 60-70 mph as winds veer northwesterly, though many areas could experience gales – particularly with passage of a cold front sweeping through later on Sunday. Cold polar air will be driven south behind the cold front, with the freezing level in the atmosphere lowering enough to allow some snow over the tops of the Scottish mountains by Monday morning.
So what’s fuelling this early Autumn wind storm? Well, with the increasingly shorter days and longer nights, the air is cooling down rapidly now across NE Canada and Greenland. While at the same time, warm moist air of sub-tropical origin is drawn north across the northwest Atlantic over the next few days, dragged up by Tropical Depression Gabrielle – which will track NE from Bermuda towards New Foundland by Saturday. The steep thermal gradient developing between the cold dry polar air to the north and warm moist tropical air to the south will help strengthen the jet stream over the North Atlantic, with a 180 mph+ jet streak moving out of NE Canada and NW Atlantic towards the UK over the weekend. A deepening area of low pressure looks to form in the left exit of this jet streak on Sunday. The left exit area of a jet streak tends to favour rapid deepening of lows, as wind aloft tend to diverge/spread out in this area which creates a kind of void or vacuum which must be filled, so air converges at the surface and rises creating a deepening area of low pressure towards the surface.
As well as high winds, the low will likely bring alot of rain ahead of it – particularly across windward western coasts across the north and northwest of Britain. So we will certainly be keeping a close eye on this system over the next few days.
