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 9th September to Tuesday 14th September
So the EC is suggesting that low pressure will dominate the weather across the UK on Thursday with it moving Northwards. Bringing rain and showers to the islands and these will be heavy at times with brisk winds. Onto the Friday and the low pressure system clears away to leave a showery start to the day for the Western Isles before becoming drier and brighter with sunshine and cloud. Winds easing as well. Becoming cooler after a warmer mid week. For the Saturday and low pressure sits to the South West of the UK high pressure to the East. For us in the Western Isles it would be a showery morning and afternoon but high pressure would build in later in the day to give fine dry conditions to end the day. Sunday and the high pressure declines away Northwards and showers will push across the UK but for us in the Western Isles it should be a mainly dry day with sunshine and cloud. Light winds. For a week on Monday the EC is suggesting that there will be a slack airflow across the UK with sunshine and cloud and a few scattered showers for the Western isles. a band of heavy rain will move westwards but not expected to reach the Western isles before the end of the day. For the final day Tuesday low pressure sits out far to the West which will bring rain and showers across the Western Isles with some heavy rain a times. Winds possibly reaching gale force.
GFS – Thursday 9th September to the Saturday 18th September
So the GFS is suggesting that a couple shallow areas of low pressure will move across the UK on Thursday this will bring breezy conditions to us in the Western Isles with rain and showers. Friday the low pressure systems clear away and behind high pressure attempts to build in. For us in the Western Isles we would see rain and at times this would be heavy before becoming drier and brighter later. For the Saturday, Sunday and Monday the GFS is suggesting that high pressure builds back across the UK with fine dry weather and light winds. Plenty of sunshine and variable amounts of cloud with some light evening rain on the Saturday for us in the Western Isles. Tuesday again high pressure dominates but some showers moving down from the North to start the day for the Western isles but this clearing to leave a fine dry and sunny end to the day. The final four days of this time period and the GFS is still showing high pressure in charge with fine dry and sunny weather but towards the end of the time period winds will increase and some showers would move in with some rain for the Saturday as low pressure moves in from the South West.
Due to active hurricane season there is some uncertainty and lower confidence in the long range forecast.
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