Thinking of Scotland or Ireland and maybe Scandinavia in late October. Will the weather permit outside activities?
Yes, but it will be chilly and the days will be rather short. You'll want to bring warm layers and rain gear.
You can get weather history for various locations at Weather Underground. For example, here's the weather history page for Edinburgh Airport https://www.wunderground.com/history/airport/EGPH/2015/7/30/CustomHistory.html
Do you have rain gear? We went in July of this year and I have never been so wet in my life. Waterproof boots are a must. We didn't mind the weather as we are Vancouverites. But it is hit and miss whenever you go. Dress for the weather and go for it.
Also remember to protect your electronics- one of our cell phones died a majestic death on Skye through the pocket of a coat. It was that wet.
That said- loved it. .
Plan for the worst and hope for the best. I was in Scotland for 8 days in mid-October 2015 and the weather was positively lovely. Chilly mornings but 60 degree +/- afternoons, just a couple of light drizzles here and there never lasting long, and beautiful autumn sunshine.
One of the problems is that many of the historic sights such as Castles start to close for the season. Check with Visit Scotland and Historic Scotland online sites for specifics and money saving discount passes. In Ireland you could just Pub Hop. I'm sure you could find something fun to do in Scandinavia; if you can afford it.
I was in Scotland October of 2016. It was warmer than usual. I walked for miles every day. Almost everyday I ended up wearing a long Eddie Bauer sweater that was 30% wool, a scarf that was long enough to wrap around and tie (the wind you know) and some wool sock and boots. Layers. I had the rain gear and wool hat on standby. Next time I go I am going to purchase as I go. There are some really good outdoor shops in Edinburgh, Tiso is one.
I was just in Ireland in late October/early November, and it was lovely -- chilly, but lovely! :-) We were in Dublin, Galway, the Aran Islands (Inish Mor) and Belfast, and although there was a bit of rain occasionally, it wasn't bad at all.