Here's what I would do.
I've done this for a looping time-lapse animation, so here's how I did it to make it look smooth.
Take each image of the sequence (ie - image1, image2, image3) and create separate graphic symbols for each (insert gif/jpg/whatever) then convert to symbol (f8) and name appropriately.
Im sure you know how to do all this, I'm just being explicit in an attempt to be clear.
Create a movie clip - clouds
Layer1 - image1
Layer2 - image2
Layer3 - image3
There are 2 methods:
1 - time-lapse / movie mode
layer 1 - frame 1- the keyframe for image 1
layer 2 - frame 1 empty, frame 2 has keyframe
layer 3 - frames 1+2 empty, 3rd frame has keyframe of last cloud sequence
To prevent the jump, create a 4th layer (bottom-most layer) and put a keyframe of clouds1 under the clouds 3
Tween the image3 image from 100%alpha to 0% alpha (using OUT or IN to acheive the desired effect).
End the movie
Make sure that each image is only on the stage for 1 frame (or however many frames you want them to last depending on your framerate and the framerate of the source clouds animation)
2 - Fading animation
Do the same as method 1, except, tween all images to fade out over the previous image.
Remember to do the keyframing tip i gave you for the looping sequence (insert keyframe before final keyframe, remove final keyframe for a better loop).
You may want to experiment with this layout, as these methods work differently (visually) with different types of images and animations.
I've linked a small screenshot for example.
Let me know if you need anything else -
Tim
Referring URLs
www.swiftcec.com/uploads/clouds_animation.gif