You never know about October, let's say from the 15th to Halloween. In the last several years we've had hot Octobers and mostly t-shirt weather---in the Southern Apps.
In 2017 I did a trip from Oct 19 to Nov 8 and needed my capilene hoody top and my acrteryx rain jacket and saw alittle snow.
In 2016 I was out from Oct 15 to Nov 4 and it was t-shirt weather and the hoody with no snow.
In 2015 I went from Oct 18 to Nov 6 and started out in a t-shirt and silk long sleeve top.
In 2014 Oct 21 to Nov 10 I started in a t-shirt and ended up wearing full winter layers in a Halloween snowstorm.
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This is the general October outfit for backpackers.
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For the Halloween snow this is how they were dressed.
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And after a 2,000 foot hump this is what they looked like.
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This is at 5,000 feet in late October and shows how much crap I needed to stay warm---merino leggings, Icebreaker merino top, gloves, turtle fur cap etc.