Long range weather forecast for the Western Isles – 4th July 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 8th July until Saturday 17th July.

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 8th July

Some good model agreement for next Thursday with both the EC and the GFS building high pressure across the UK. Both models show a rash of afternoon and evening showers breaking out across most of the UK. For us in the Western isles it should be a mainly fine and dry day the odd isolated shower is possible. The GFS has more in the way of sunshine compared to the EC which keeps us more overcast. 

Friday 9th July

High pressure continues to dominate the weather across most of the UK for next Friday. Both the EC and GFS are in good agreement about this. There are some slight differences with EC keeping things drier with sunshine and cloud across the Western isles with light winds. The GFS on the other hand has more in the way of cloud after a dry start and a weather front pushes in as we go into the afternoon and evening bringing with it some rain for a time. 

Saturday 10th July

Some model differences for next Saturday. The EC brings rain and showers to much of the UK with low pressure moving along the channel. For us in the Western isles we would see a fine and dry day with sunshine and clouds Winds would be light and feeling warm. The GFS on the other hand sends a band of mainly light rain across the Western Isles during the overnight period and then showers for the rest of the period along with brisk winds as an area of low pressure moves to our far North West. 

Sunday 11th July

Further model differences for next Sunday. The EC again keeps the high pressure dominated across the UK with sunshine and cloud with the odd scattered shower. Winds will be light. The GFS moves rain and showers across the Western isles during the morning with plenty of cloud along with brisk winds. Becoming drier and brighter for the afternoon and evening before the next system moves in. 

Monday 12th July

Once again model differences for next Monday. The EC suggests a showery airflow across the Western isles and much of the UK but these become confined to the North Sea as high pressure builds back across the UK from the West. The GFS sends an area of low pressure across the North Western isles which would bring heavy rain and winds gusting to gale force. A long way off as yet but with keeping an eye on the trend. 

Tuesday 13th July

Again further model differences. The EC has high pressure across much of the UK but some rain and showers move into the Western isles. High pressure builds in later in the day. Before another low pressure system builds to the West. The GFS has a low pressure system to our North and this would bring rain and showers along with brisk winds. Becoming drier and brighter with sunshine later in the day. 

14th, 15th, 16th and 17th July

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 a spell of wet and windy weather across the Western isles before becoming fine dry with sunshine and cloud with high pressure for the final 3 days. 

Featured photo comes from Murdo Macaulay

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