Disclaimer: The information provided on this website is not and should not be taken as medical advice. You should always consult a veterinarian regarding your pet's health.
Yowling is a noise that a cat uses just for humans; meaning cats never yowl at each other. It is more aggressive than just a meow and it's their way of communicating to you that they want something or that they are stressed out.
If your cat yowls at you, the first thing to do is access the situation to see what the cause is. One of the most common reasons why a cat yowls is because it is hungry. So the first thing to do is check whether or not there is food in his/her bowl. Your cat could also be yowling because it is trapped behind a closed door and wants to get out of that room.
An example of this is when your cat follows you into the bathroom and is then trapped inside with you and wants out. Your cat could also be yowling for attention, which is especially true if you have been out all day. The worst case scenario is that your cat is yowling because he/she is in pain. If this is the case than you should take it to the vet as soon as you can.