I am going to take him to vet, but wondering what this might be? The weather is horrible windy and wet but he will be an inside dog. he was neutered 4 days ago.

Upper respiratory infections are common after anesthetic on shelter animals. Stress, poor nutrition, etc. don't make for the healthiest animals and then they have the stress of surgery. and of course kennel cough is almost a guarantee in shelters. The good news is that both of these are usually self limiting. in extreme cases they can be problematic but most of the time you just need to keep the pup isolated (don't want to give it to another dog) and quiet. Vet will probably put it on antibiotics or other meds as a precaution but usually time and supportive care is all that is needed. enjoy your new friend!!!