Navajo has several words that differ between regions. Such is the case with snow.
Since the creation of state lines, the word yas has generally been used by people who live on the western side of the Arizona/New Mexico border. On the eastern side, zas is employed more commonly.
Using either word can give a conversational partner or group some context as to the general area one comes from. This is a reliable distinction because most people use a particular word form throughout their life.
For me, it’s yas.