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 Monday 3rd May until Wednesday 12th May
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.
Monday 3rd May
Good model agreement for next Monday that a deep area of low pressure will rattle in off the Atlantic bringing strong winds and rain to much of the UK. The EC tracks the low a bit further south so the very worst of the stronger winds would miss us on the Western Isles and we would see rain and showers. Brisk winds and some snow falling over the higher ground of mainland Scotland. The GFS tracks the low pressure further North between us and North Ireland. This would give us some very heavy rain and brisk winds which could reach gale force for a time before clearing away late evening.
Tuesday 4th May
Some good model agreement from both the EC and the GFS which moves Mondays low into the North Sea. This will allow colder air to move down from the North. We are going to see a day of sunshine and showers some of these will be wintry showers moving across the islands. Brisk winds and feeling cold. The GFS runs a secondary low across the Southern half of the UK.
Wednesday 5th May
Some model differences for next Wednesday. The EC continues the strong wintry airflow across the Western Isles with sunshine and showers. Again some of these wintry at times and it would feel cold. The GFS has the cold and wintry airflow moving down from the North to start the day but this airflow eases late morning. We will then mainly see a fine and dry day with sunshine. A next area of low pressure moves in from the West bringing rain into North West England and Northern Ireland.
Thursday 6th May
Again further model differences. The EC has low pressure over Scandinavia. This will drive cold air down across the Western Isles. A day of sunshine and showers these will be heavy at times with some sunny spells at times it would be breezy. The GFS on the other hand suggests that low pressure will move around North West Scotland and bring rain and showers. The rain heavy at times with blustery winds.
Friday 7th May
Some slight model agreement for next Friday. Both models suggest that an area low pressure will move in from the South West. The cold airflow will cut off from the North. The EC shows a deep area of low pressure moving into South West England with strong winds and heavy rain. For us in the Western isles we are expecting to see a showery start to the day but becoming fine and dry day later with sunshine and cloud. The GFS has a much deeper area of low pressure moving into Ireland. This would bring strong winds and heavy rain. This rain could move into the Southern half of the Western Isles. Mainly fine and dry further North you are.
Saturday 8th May
Some model differences for next Saturday. The EC brings the low pressure across the UK and slowly weakens bringing rain and showers. For us in the Western Isles we would see a day of brisk winds and sunshine and showers. The GFS moves the strong area of low pressure across the UK. We would see brisk to strong winds across the Western Isles along with some heavier rain later in the day.
9th, 10th, 11th and 12th May
Now this is the really long range. So take it with a large amount of salt and is the silly range. So with the GFS it suggests that high pressure will build in behind the above mentioned low pressure system. Then for the final 3 days of the time period we would see further low pressure systems bringing rain and blustery winds.
Featured photo from Isi Oakley at Aird Mangasta