Smooth Window Resize

I am looking to animate the form shrinking. [not sure if this is the best way to describe it] 
I have a list that changes based on user selection.
When the list grows i scroll to the bottom to keep the next button in view. [using jQuery scroll to, to make this animated]
When the size of the form shrinks its not smooth, so i was wondering how i would animate this and make it a little smoother.
eg: Max scroll is 1000. [all fictitious #] 
User selects option 1: max scroll is 1500[jQuery Scroll To 100%]
User selects option 2: mas scroll becomes 1000 [would like to smooth the transition just dont know ware to start]
 
 
THANKS IN ADVANCE!!!!!
 
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