Welcome to the our long range forecast for the Western Isles. This is our twice weekly update covering up to two ahead. We look at trends and patterns. Usually posted on a Thursday and Sunday.
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.
EC – Thursday 16th September to Tuesday 21st September
The EC is suggesting that high pressure will still be across the UK on Thursday but low pressure will move towards the UK as the day goes on. A dry start for us in the Western Isles with sunshine and cloud but winds will increase with rain moving in and it will become heavier later in the day.
Into Friday and the band of rain moves across the UK with a new area of low pressure forming towards the East coast of England for us in the Western Isles some overnight rain which will clear away as low pressure clears away. A ridge of high pressure builds becoming fine and dry with sunshine and cloud.
For the Saturday the bridge of high pressure gives us a fine and dry start to the day with sunshine and cloud but the next area of low pressure will bring further rain and showers later in the day. High pressure builds again across the South East of the UK.
Sunday spells of rain which would be heavy at times as the area of low pressure moves across Scotland with brisk winds for us in the western Isles.
Into Monday and the low pressure moves across Scotland and after a showery start conditions would become more settled across the Western isles as ridge of area of pressure builds in again. But more rain moving in later in the day before the next area of low pressure moves in.
Tuesday the above area of low pressure moves across Scotland bringing some heavy and at times persistent rain with a risk of gales for us in the Western Isles. The rain would last throughout the day.
GFS – Thursday 16th September to the Saturday 25th September
The GFS is suggesting for the Thursday that high pressure is in charge across the UK to start the day with sunshine and cloud but a band of rain in association with an area of low pressure to the North West will bring rain later in the day along with increasing winds.
Into the Friday the band of rain clears away but high pressure ridge will bring that will gives us a drier and fine day with brisk winds. The band of rain will die out as it moves across the UK.
Saturday and Sunday we are going to see a mixture of sunshine and cloud with brisk winds. Possibly gale force at times with rain and showers.
Monday low pressure moves into Ireland then into Southern England it will bring some rain and showers to the Western Isles with some sunshine. Later in the day high pressure builds across Northern Scotland resulting in drier and sunnier weather to end the day.
Tuesday a fine and dry day with sunshine. Decent and prolonged sunshine and it would be breezy. As high pressure strengthens.
The final 4 days of the time period and high pressure would dominate mainly fine and dry the first 3 days. With a slight chance of rain. But later in the day on Friday a band of rain would move down from the North and bring increasing winds and showers for the Saturday.
Due to active hurricane season there is some uncertainty and lower confidence in the long range forecast then normal.
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