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 coving from Thursday 17th December until Saturday 26th December.
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 which is based in Reading and the GFS 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 17th December
Some model differences for next Thursday with the EC bringing spells of heavy rain across the Western isles and blustery winds. Winds would gust 30 to 40 mph. This would be associated with a low pressure system to our North West. A weak area of low pressure. The GFS keeps things dry for most of the day across the Western Isles before rain moves in later in the day. Lighter winds. An area of low pressure moves across the islands but weakening all the time.
Friday 18th December
Both the EC and GFS has good agreement with low pressure dominating our weather next Friday. The EC first brings rain during the early morning then further rain in the middle of the day before a dry end to the day. Low pressure sits to the South West of the Western Isles and another low pressure between Wick and Orkney this will bring blustery winds. The GFS brings showery rain and sunny spells for most of the day before a deeper area of low pressure brings in heavier rain later in the day.
Saturday 19th December
Both models have low pressure system in charge of the Weather in North West Scotland. The EC has a shallow area of low pressure across the Western isles with sunshine and showers. The winds would gust 40 to 50 mph. The GFS has low pressure closer to the West coast of mainland Scotland with blustery winds with spells of heavy rain at times.
Sunday 20th December
Again some model differences so the EC builds high pressure over the Southern half of the UK with blustery winds over the North. Here in the Western Isles it would be a day of blustery winds and squally wintry showers. The GFS has low pressure in the North sea and this would introduce colder air across the Western Isles but this is expected to be dry but breezy.
Monday 21st December
The EC has the brisk wintry and squally airflow persistiting for the first half of the day. Then winds increasing later with rain moving in and becoming heavy. Winds increasing. The GFS brings rain and showers across the Western Isles as a result of an area of low pressure to our far South West. Feeling milder.
Tuesday 22nd December
Good model agreement with low pressure system dominating our weather across the Western Isles with spells of rain which will be heavy at times. Winds would gust 30 to 40 mph. The low pressure system would sit to the far South West and bring spells of rain.
23rd, 24th, 25th and 26th December
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 suggests that cold air will move across the Western Isles on Christmas Eve with wintry showers on Christmas Day and then high pressure for the final two days of the time period. A lot can and will change between now and then.
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