It is very hard to separate from your GIF animation where the GIF is looping and where a potentially sharp transition happens.
Although it's using the SkeletonAnimation component, you can have a look at the example scene Spine Examples/Getting Started/5 Basic Platformer. Here the Hero skeleton only uses the jump animation during the rising (where velocity.y > 0) part without any jump-start intro-part. Typically you want a very short transition (to achieve direct input feedback) which is fine when left to the animation transition blending.
I'm not sure why you would want to use a blend tree depending on vertical velocity here, typically you will only play animations in succession: first rising, and then falling, then a landing/impact animation. My guess is that your blend tree will cause problems since the JumpLand animation is not a loop which can start at any time, is that right?
