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 6th May until Saturday 15th 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.
Thursday 6th May
There is good model agreement for next Thursday with rain moving down from the North across the Western Isles and this will be heavy at times. Some early rain could fall as sleet for a time with snow on the hills of mainland Scotland. Winds gusting to gale force at times and feeling bitterly cold in the wind. Both the EC and GFS have agreement on this.
Friday 7th May
Some slight model differences between the EC and the GFS. Both models suggest that we will see a slack airflow across the islands with sunshine and showers. Breezy but not as strong as the previous few days. Both models bring low pressure system towards the UK. The EC brings in the low to the South West of the UK and rain moves in later. The GFS has a low pressure system in the channel bringing rain here.
Saturday 8th May
Big differences for next Saturday. The EC brings the low pressure over Ireland and this would bring heavy rain over the Western Isles with some sleet and snow. Along with blustery winds. The GFS has the low pressure moving into the North Sea. For us in the Western Isles we are going to see a day of sunshine and showers. These will be wintry at times. Feeling cold.
Sunday 9th May
Again model differences. The EC suggests slow moving low pressure close to ireland. Further spells of rain and showers across the Western Isles. These would be heavy at times. Some sunny spells and brisk winds. The GFS on the other hand suggests high pressure to our far North West with a cold airflow with sleet and snow showers. Rain at times with a brisk winds.
Monday 10th May
Some good model agreement from both the EC and the GFS. The low pressure system will clear away from ireland according to the EC and high pressure builds in. A showery start then drier later. The GFS suggest a showery start but high pressure builds in and becomes drier and brighter with lighter winds.
Tuesday 11th May
Again model differences. The EC send a low pressure in from the East which would bring heavy rain across the islands and blustery winds. The GFS shows high pressure across the UK and it will be fine and dry with sunshine and cloud with lighter winds.
12th, 13th, 14th and 15th
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 a mixed spell of weather changing between high pressure and further spells of rain.
Featured photo – Looking towards St Kilda taken by Cat Wright