The west coast of Scotland weather has attracted vigorous comment for decades, from the positive by John Inglis in 1879: "The one thing certain about Scottish weather is that it cannot be called monotonous, and that is a great matter; probably if the country had the climate of the Sinaitic desert its scenery would be quite as dismal" to the negative by Frank Cowper in 1896: "I find I am constantly being blamed for the Scotch weather; but I do think statistics back me up, even if enthusiasm leads the devotees of the W. coasts to forget the rain and the endless alterations in the force of the wind. All those who have honestly written of the W. coasts have decried the abominable weather from Boswell and Dr MacCulloch to the compilers of the Admiralty Official Directions". Personally I am a 'devotee' and prefer the 'Scotch' weather to the unruly crowds of the south coast of England. As did CC Lynam in 1907: "Many people grumble at the Scotch climate. Our first experience of it gave us no cause for discontent: plenty of sunshine, lovely sunsets, unrivalled cloud effects, very few days of persistent rain". In the end it all boils down to getting out and about despite the weather just as Robert Buchanan did when he wrote in 1871 "To abide indoors on account of wet or lowering weather may do very well in Surrey, but it will not do in Lorne." but, as always, in the right kit which in his day was "a suit of thick tweed such as any cottar weaves, cut a stick from the nearest blackthorn bush, and sally forth in all weathers. Let your boots be just easy enough to let the water out when it has managed to get in, and you will be quite comfortable"
If you want the forecast, you could look at the sky, then at the barometer, and then back to the sky before passing judgment. Or you could do what the rest of us do, either listen to or more often bring up the relevant websites.
More and more I use the very useful and amazingly accurate xcweather app. giving wind, temperature and rain forecasts for up to seven days ahead. And windy.com. But less and less often, the Met Office (for the land forecast) along with the relevant sea areas: the inshore waters forecast from the Mull of Kintyre to Ardnamurchan Point, from Ardnamurchan Point to Cape Wrath, and the Minch. Contrary to some very strongly held beliefs, I find these Met Office forecasts very good. If anything they seem to over emphasise the likely problems, which is the right way round.
And you could take a look at the weather on the ground at the time by looking at various webcams in the area although I must confess I usually look at them to reassure myself that I did the right thing by staying put.