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 covering from Thursday 19th August until Saturday 28th August.
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 ( European Centre for medium range weather forecasts) which is based in Reading and the GFS (Global forecasting system) 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 19th August
For next Thursday the EC is suggesting a slack airflow across the UK with high pressure rain and showers. For us in the Western isles a mixture of sunshine and cloud with mostly light winds. The GFS on the other hand has an area of low pressure to the West of the UK bringing spells of ran and showers to parts of the UK for us in the Western isles we are going to see a mixture of sunshine and cloud. Some decent and prolonged sunshine with mainly light winds.
Friday 20th August
Some good model agreement for next Friday. Both the EC and GFS has an area of low pressure to the South West of the UK which would bring rain and showers again to large parts of the UK. The GFS has the low pressure a little further South West then the EC. Both models keep conditions fine and mostly dry across the Western Isles with some decent and prolonged spells of sunshine. Winds would be mostly light. However the EC has the winds slightly stronger then the GFS. The odd scattered shower would be possible.
Saturday 21st August
Some slight model differences for next Saturday. The EC moves the area of low pressure mentioned above across the UK. For us in the Western Isles we would see brisk winds with sunshine and cloud. Occasional scattered showers but most places would be dry. The GFS keeps low pressure close to Ireland bringing further rain to parts of the UK. For us in the Western Isles it will be a largely fine and dry conditions with sunshine and cloud. A few scattered showers. Winds again will be brisk.
Sunday 22nd August
Again further model differences for next Sunday. The EC builds high pressure across the UK. For us in the Western Isles we would see fine and dry conditions with sunshine and cloud. Winds would be light and the odd scattered shower would be possible. The GFS keeps low pressure in the Irish sea bringing further spells of rain for parts of the UK for us in the Western Isles we would see mainly fine and dry conditions with sunshine and cloud. Winds will be light.
Monday 23rd August
Some slight model differences again for next Monday. The EC keeps settled conditions for much of the UK but an area of low pressure forms across central parts during the day. For us in the Western Isles we will see a mixture of sunshine and cloud with a few scattered showers. Winds would be light. The GFS keeps high pressure across Scotland with low pressure for South East England. Fine and dry conditions for us in the Western Isles with sunshine and cloud. Winds would be light. Decent and prolonged sunshine.
Tuesday 24th August
Little change for the Tuesday. The EC keeps things mostly settled across the UK mainly fine and dry with some rain at times. For us across the Western Isles we would see fine and dry conditions. Some sunshine and cloud. Winds would be light. The GFS keeps high pressure close to Shetland extending across the Western Isles with some decent and prolonged sunshine. Variable amounts of cloud. Winds would be light.
25th, 26th, 27th and 28th
Now this is the really long range. So take it with a large amount of salt and is the silly range. So the GFS is suggesting that the first two days of the time period would be fine and dry with sunshine and cloud. Rain and showers with more unsettled conditions for the final two days of the time period.
Thanks for reading any feedback is welcome our feature photo comes from Jane Maciver of Stornoway