The WAT chart is - as j_t said it - just a certification requirement. The only information you can deduct from it is:
1) Operating on "inside" of the WAT envelope - the aircraft is a SFAR23/FAR25 (don't remember which the J31 is
) aircraft
2) Operating on "outside" of WAT envelope - the aircraft is an experimental aircraft.
The WAT tables provide absolutely no information on weather you will be able to depart/land at any specific airport under a specific set of weather conditions. Therefore, operationally, they are of very limited interest. Yet - some manufacturers (Raytheon/Beech for one) headline these WAT graphs as
"
MAXIMUM TAKE-OFF WEIGHT to achieve takeoff-climb requirements...". The unsuspecting / less well educated in-duh-vidual may be led to thinking that this graphs actually give you the restricting take-off weight...
Brgds,
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