Is there a way to transition between 2 textures? I have searched extensively and all the help seems to be having 2 textures next to each other and making a smooth transition between them. This is NOT what I want. I want to have 2 cloud textures overlapping and have 1 see invisible and the other one opaque. I then want the opaque one to slowly disappear as the other one becomes visible or even have them blend into each other as they change from one to the other. Is this possible?
You may want to consider MixRGB or Mix Shader node to achieve this effect. 

In the example gif I provided I plugged two different noise textures into a MixRGB node to blend between them, you could animate the 'Factor' slider using a 'value' node. You can also Change the mix dropdown to another blend type, such as add, multiply, or overlay (similar to blend types in photoshop). The resulting mix is then plugged into the Base Color for the Principled BSDF Material.

Hope this helps.