This is high desert country. The Oaxaca valley is 6,000 feet elevation surrounded by 9-12,000 foot mountains. Winter days are high 60’s to mid-70’s, and can sometimes inch up to the 80’s, especially in a sunny, protected corner of a bougainville draped patio. I recommend dressing in layers, especially if you’re out for the day and will continue on into the evening after the sun goes down without benefit of a stop back at your place of lodging. Nights can get down to the low 50’s or high 40’s. Brrr, chilly. I always wear cushy wool or polypropylene socks because they allow my feet to breathe and stay warm, even if they get a little damp from too much hiking around. My Keene low-rider hiking boots can keep me going on the cobblestone streets or dirt trails for a good 12 hours with reasonable comfort. These are the basics that I take for the winter visits:
wool socks, long-sleeve wool or polypro T-shirts, a fleece vest, wool sweater, wool or chenille scarf, synthetic quick-dry hiking pants with secret hiding place pockets for money and passport, a long-sleeve cotton dress, outer jacket, sun hat for days, knit cap for evening, sunglasses, extra reading glasses, sunscreen, moleskin. You may even want to pack a pair of shorts and bathing suit — it’s tropical hot at the coast.
The daytime sun is strong enough to dry your clothes on a line the same day, even within hours, so there’s no benefit to packing more than you need. The shopping is GREAT in Oaxaca and the surrounding villages and prices are VERY reasonable, so what you don’t bring you can easily buy. Don’t forget, there’s Sam’s Club in Oaxaca and Fabrica de Francia that even carries Liz Claiborne! It’s not the end of the earth.