Good afternoon and welcome to our long range forecast. This is posted either once or twice a week covering from 4 days ahead to 10 days ahead. In this update coving from Thursday 26th November until Saturday 5th December.
Please note there is not a lot of accuracy for this kind of time frame. Anything beyond 4/5 days out becomes really difficult and subject to change so we will be looking at trends. Mainly take with a large vat of salt. We will be using the main two computer models for this. The ECMWF which is based in Reading and the GFS which is the American based global model.
This comes from the GFS 06z run and ECMWF 00Z run. I will refer to EC to save on typing.
Thursday 26th November
Good model agreement with regards to next Thursday with high pressure in control across the UK. For us in the Western Isles we are going to se blustery winds. A dry start with the EC suggesting light rain moving in later in the day. The GFS keps the dry day. It would be a chilly day. The EC has high pressure centred over the North East of England and the GFS has it centered over Wales.
Friday 27th November
Some slight model disagreements here. Both the GFS and the EC has the high pressure system declining back into Europe. The EC keeps a band of rain out in the Atlantic and mainly dry for us in the Western Isles. However the GFS brings the band of rain across the Western Isles with a showery airflow behind it.
Saturday 28th November
Model disagreements again for next Saturday with the EC again keeping us mainly dry and with light winds. A slack airflow across the UK. The GFS introduces further spells of rain and strengthening winds which would bring gales. High pressure to the East of the UK and low pressure to the South West in this instance.
Sunday 29th November
Now both models develop an area of low pressure that would be run up from the Irish Sea. This would bring heavy snow into the highlands of Scotland. However the GFS builds in a shallow area of high pressure over Scotland. The EC does no. Both these scenarios would bring patchy rain and showers to the Western Isles and it would be breezy.
Monday 30th November
Model disagreements on this date with the EC bringing a dry start to the day for the Western Isles before rain and stronger winds would move in later in the day. The GFS on the other hand builds in the high pressure in further. Keeping things fine and dry with a mixture of sunshine and cloud with lighter winds.
Tuesday 1st December
Further model disagreements as we move into December. The EC develops two areas of low pressure that would bring wet and windy weather to the Western Isles with gales. The GFS keeps high pressure centred over the East coast of Scotland. This would mean fine dry and sunny weather for the Western Isles with light winds.
2nd, 3rd, 4th and 5th December
Now this is the really long range. So take it with a large amount of salt and is the silly range. The GFS keeps things settled across the Islands. A chance of some rain towards the end of the time period but nothing to extreme. No storms on the horizon.
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