Just like a baby; They need warm clothes, blankets, and boots. They shouldn’t walk around outside if its any colder than 35F, and I’d say they should be in a sweater from 35-55F. But some chihuahuas shiver all the time, so it will be a learning process. Their feet should be protected from snow, and you should cuddle them to sleep under your blankets. Yes.
Thankfully, Washington doesn’t get too cold, but definitely colder than Texas.