Create a basic Animation to show the rain drop animation
1.Open a new flash document on layer1 draw a cloud or take a cloud in the timeline.
2.Insert a new layer2 & draw the raindrops using brush tool at this time select the brush shape as line & draw the more than one raindrop on layer2 & select the color from fill color option.
3.Insert an again new layer3 & draw the lightning bolt or take the Lightning bolt.
4.Select the raindrop layer2 & click on any frame30 or as per your choice & press f6 (insert keyframe), right click on frame1 & choose create motion tween click on any frame in between selected frame e.g. (click on frame15 in between frame1 to frame30). & press f6(insert keyframe) & change the position or move the position for raindrops also click on selected frame(e.g. Frame30) & also change the position or move the position for raindrops.
5.Select layer1 i.e. cloud & select the same frame & press f6(insert keyframe)
6.Select layer3 i.e. lighting bolt & select the same frame & press f6 (insert keyframe) & also click in between the frame1 & frame30 (i.e. frame 15) & press f6.
7.Save your work & test the movie