Eh, that is a tough one. The Tat聴or Tatshenshini River聴is known to be rough, technical聟and cold.
The Alpha SLSo layer up, Andrea. I聮d start with good lightweight wool, as it has good insulation properties even when damp or wet and in my experience is a better “regulator” of temperature than synthetics. The Bodyfit 200 Shakra Zip Top ($75) and matching leggings ($60) are an excellent start.
Then, a good heavy but snug layer, such as ‘s Capilene 4 Zip-Neck ($85), an “expedition weight” layer that will be your favorite piece. In many cases, the Icebreaker and Patagonia pieces, worn under a shell such as the Alpha SL ($300, made with Gore Pac-Lite) will be enough.
But for extra warmth, I like something that has fluffier insulation than fleece. Something like ‘s UL Thermawrap Jacket ($145) which has a smooth nylon shell for easy layering, and synthetic insulation for water-resistant warmth.
Gloves are the other critical piece. ‘s Women’s Gripper Gloves ($45) are a good start. Find some Woman’s Epic Gloves ($40) that fit over the Grippers. They’ll give you a shell for extra water and wind protection.
Buy a couple ten-packs of Graber聮s Hand Warmers ($10 a pack) as well. Just put them in your gloves for extra warmth.
I聮ll let your guide recommend the best footgear. Probably going to be a combination of neoprene socks and wool socks. Take plenty of dry socks!