1) Aleatory 2) Capricious 3) Changeable 4) Dicey 5) Erratic 6) Fluky 7) Freakish 8) Idiosyncratic 9) Impulsive 10) Indecisive 11) Indeterminable 12) Random 13) Risky 14) Sporadic 15) Tricky 16) Undeterminable 17) Unforeseeable 18) Unstable 19) Untrustworthy 20) Variable 1) Aleatory 2) Capricious 3) Changeable 4) Difficult 5) Episodic 6) Excitable 7) Explosive 8) Freakish 9) Hard to forecast 10) Highly strung 11) Inconsistent 12) Irregular 13) Moody 14) Not capable of being foretold 15) Not predictable 16) Occasional 17) Uncertain 18) Unforeseeable 19) Unknown in advance 
[adj] - impossible to foretell 2. [adj] - unknown in advance
adjective unknown in advance; `an unpredictable (or indeterminable) future`
not predictable; not to be foreseen or foretold: an unpredictable occurrence.