Here is an idea, an outline now, have to work on the details.
If you judge the weather on TZ-1 to be too unfavorable for you to bomb the target you may change the altitude and go lower.
1. Enter the Target Zone.
a) Roll on TZ-1 for Weather. If you judge the weather to be unfavorable to you go to b).
b) Roll on Mission Planning Table 2 (MP-2) Mission Altitude.
c) The result on MP-2 is the altitude for the new weather condition from TZ-1. If the result is your altitude, the new weather is lower. If the result is higher, the weather is at your altitude.
Example: The new weather condition on TZ-1 is Bad. Your altitude is Column C, 10000 feet. The c)-roll on MP-2 says Column C.
I thought I had time to finish this post today... I will post this short message, and then come back and edit it. Here is an image which I am using to illustrate my idea and to help me think about how to use the existing rules and tables... It may also be helpful to you to see what he steps in the Target Zone are. It is small though...