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 2nd September until Saturday 11th September.
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 2nd September
Good model agreement from both the GFS and EC showing high pressure across the UK. The EC has slightly more cloud with some light rain and drizzle but for the most part dry. The GFS has high pressure dominating as well with more in the way of sunshine and light winds. The EC has a very weak area of low pressure across central Scotland.
Friday 3rd September
Again more model agreement for next Friday with both the GFS and EC showing high pressure dominating across the UK. The EC has mainly overcast conditions with some sunny spells with scattered showers. But for most it will be mainly dry with sunshine and light winds. The GFS has a mixture of sunshine and cloud. Some decent and prolonged sunshine. Feeling warm. Brisk winds.
Saturday 4th September
Some slight changes for next Saturday. As high pressure relinquishes its grip. The EC show a mostly overcast conditions with some light rain and winds would be brisk across the Western isles. Rain moving in Ireland as high pressure moves away. The GFS shows a mainly fine and dry start to the day with sunshine and cloud for the Western Isles. A weakening weather front will bring spells of rain into the West of the UK. These will arrive as showers into the Western Isles later in the day.
Sunday 5th September
Model differences for next Sunday. The EC shows a mostly fine and dry day for us in the Western Isles with sunshine and cloud. Along with brisk winds. An area of low pressure will bring rain and and at times heavy rain into Ireland and Northern Ireland. The GFS has high pressure across South Eastern England and low pressure to the North West of Scotland. Overnight rain showers will impact the Western Isles Saturday into Sunday before a day of sunshine and cloud with brisk winds. Before further showers move in later in the evening.
Monday 6th September
Again some model differences for a week tomorrow. The EC keeps conditions fine and dry across the Western Isles with sunshine and cloud. Brisk winds. A band of rain becomes slow moving across the UK which would result in heavy and slow moving rain. The GFS has a dry night before a band of rain moves in from the West resulting in heavy morning rain and brisk winds. The band of rain would clear away during the afternoon to mostly fine and dry sunny conditions with brisk winds for us in the Western Isles.
Tuesday 7th September
Again some slight model differences the EC keeps areas of low pressure moving around large parts of the UK but for us in the Western Isles it should be mostly fine and dry with sunshine and cloud but those winds staying brisk. The EC has high pressure building across the UK. Winds would ease and it would be mainly fine and dry with sunshine and cloud for us in the Western Isles.
8th, 9th, 10th and 11th September
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 high pressure will give way to areas of low pressure move past to our North West bringing spells of rain and increasingly strong winds. Lot of uncertainty as yet and constant changes with the computer models but will keep an eye on. High pressure ridges do build in at times.
Our featured photo comes from Mairi Mac-Morrison taken at Stornoway Harbour.