Morelia Butterfly Tour

My wife and I and friends are taking a weekend trip from Zihua to Morelia in mid February. We will be taking a tour to see the Monarch butterflies. We have been Visiting Zihua and Ixtapa for many years but this is our first visit to Morelia. If you have been to Morelia in mid February what would you suggest to bring along for clothing for the tour and evenings in Morelia in mid February ?
We are from a cold climate and typically we get into shorts and light clothing no matter what is happening in Zihua. Any advise on appropriate attire for the climate in February in Morelia is appreciated.