Long range weather forecast for the Western Isles. 17 September 2020.

Good afternoon all this is a new blog idea that I am trying out. If it proves popular I will keep doing it. I have had a few people asking about longer range forecast updates. If this proves popular I will do it once a twice a week and will cover a forecast period of day 4 to day 10. In this update coving from Monday 21st September until Wednesday 30th September.

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. We will be using the main two computer models for this. The ECMWF which is based in Reading and the GFS which is the American based global model.

This comes from the GFS 12z run and ECMWF 00Z run. I will refer to EC to save on typing.

Monday 21st September

Seems to be some solid model agreement that a band of heavy rain will move across the islands on Monday. Heavy rain for the afternoon and into the evening. Staying mild with winds gusting to 40 mph.

Tuesday 22nd September

High pressure attempts to build back in but more rain is expected to move across the islands with the EC going for more rainfall than GFS. Some decent spells of sunshine and brisk winds but lighter than Monday.

Wednesday 23rd September

Some differences come into play here the EC suggest an area of low pressure stays further with less in the way of rain for us. However the GFS brings stronger winds and heavier rain across the islands. Something to keep an eye on but a long way off.

Thursday 24th September

More differences here the low pressure system is brought across the South of the UK bringing showery rain to us in the Western isles by the EC. The GFS brings it further North across Northern Ireland. Northern England and Southern Scotland which would bring more rain for us. But as we are talking about a low pressure system that doesn’t even exist it’s all theoretical.

Friday 25th September

Both models have agreement on some sort of cold plunge after the low pressure passes the UK with cold air coming in from the North. The GFS suggest a shot of heavy rain as a leaving present from the area of low pressure.

Saturday 26th September.

The EC gives us a nice hint of a ride of high pressure and some more settled drier weather. The GFS gives us more rainfall and a hint of snow on the Scottish highlands.

27th, 28th, 29th and 30th September.

This is well into the silly range as the EC doesn’t even go this far out. The GFS keeps things fairly settled with high pressure dominates but fairly breezy.

Hope you have enjoyed its quite wordy but any feedback is useful.

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