mhensley said:
Can you jump up and attack something that is out of your reach? How do you resolve this and what are the attack modifiers for this?
Assuming that it is within reach of your weapon once you jump up and swing, then I would think it's possible. A liberal GM would probably allow it without even looking at the game mechanics. However, I think you are looking for game mechanics, so let's see.
If the GM declares that you have to Ready an action to attack an enemy in mid-move, then you can't jump and attack at the same time. Jumping is a move action, and an attack is a standard action, so you can jump but can't swing in time before landing if you Ready, since you can only ready a standard action. (This is by the strictest interpretation of the RAW.)
Assuming that the creature you are attacking is hanging above you, or has stopped at the end of its round within reach, then you can do the following:
First, make a Jump check to jump up in the air. This constitutes part of a move action, and your height is determined by your roll, per the Jump skill description.
Second, as a standard action, you may make a single attack against the target of your jump, assuming your weapon is in range of the target.
Since your move ended up in the air (unless you have Spring Attack), the RAW indicate that your next action must be a move action to complete the jump and land, per the Jump skill description (since Jumping is the action you have to do first in order to get high enough to attack).
Now, given that, how you do it in your game is up to you and those at your table. The above sounds a little silly to me, but it's my understanding of the RAW.
Given the above, I would suggest that you carry a ranged weapon for just such occasions as this one.
EDIT: Frank's post above (since he posted as I was writing my response and so I missed it) does point out that you may not even be able to attack in the air without Spring Attack, because the Jump skill obligates you to finish the movement with your next available action, hence you would land before you could even swing your weapon. Nice call, Frank. Yeah, either have the DM house rule it, or use a ranged weapon instead.
With Regards,
Flynn