Long range weather forecast for the Western Isles – 9th May 2021

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 13th May until Saturday 22nd 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 13th May

there is good model agreement next Thursday from both the GFS and the EC both suggesting that low pressure that has been dominating the weather across the UK moves away. Both have rain for the morning but this clears away. Allowing for drier weather with sunshine and cloud. The GFS has more in the way of cloud than the EC and both have a Northerly airflow setting up. 

Friday 14th May

again more good model agreement for Friday. The EC has high pressure dominating the weather. Winds still coming down from the North. A day of sunshine and cloud with a few scattered showers. The GFS on the other hand suggests a fine and dry day with sunshine and cloud with light winds

Saturday 15th May

good model agreement for Saturday with an area of low pressure moving in off the Atlantic bringing with it wet and unsettled conditions. The EC has a low pressure system of 1008 mb moving in and the GFS had a slightly deeper low pressure system of 998 mb. This would also bring rain and blustery winds. 

Sunday 16th May

some model disagreements for next Sunday. A North and South split for the UK weather. Better in the South. The EC moves the low pressure system away from Saturday and gives us showery conditions across the Western isles. The GFS moved the low pressure between Orkney and Shetland this would bring us brisk winds and a mixture of sunshine and showers. 

Monday 17th May

Again further model disagreements for next Monday. Unsettled conditions persist across the UK. For us in the Western isles, we would see rain and showers. A developing area of low pressure brings heavier rain across the islands. The EC moves the area of low pressure away towards Norway and the rain and winds abate. High pressure would build in with sunshine and cloud for later in the day. 

Tuesday 18th May

again further model disagreements for next Tuesday. The EC has a shallow and weak area of low pressure moving into Ireland. For us in the Western isles a few showers and plenty of cloud. The GFS on other hand pushes in a deeper area of low pressure past the West of the UK. Now plenty of uncertainty at this timeframe and the low pressure system is currently expected to stay our to sea and we would just see some rain and showers with blustery conditions.

19th, 20th, 21st and 22nd 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 for the final four days of this period, the situation looks to stay unsettled with more spells of rain and blustery winds as more areas of low pressure move across the UK. 

The featured photo is Carloway taken by Cat fitzsimions

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