My family is from there, so I've experienced Alamosa in just about every weather extreme over the last 31 years...

Sunny and warm during the day, absolutely freezing at night. Remember, you're at 7000+ feet. Jeans and a two layers up top (beanie just in case) should be good for the week. I've never seen snow on thanksgiving in Alamosa, it's usually sunny and in the 50s, however plan on high teens at night