▁occur ▁when ▁temperature ▁decre ases ▁pole wards ▁( to ▁the ▁north , ▁in ▁the ▁northern ▁hem is phere ), ▁and ▁pressure ▁perturb ation ▁lines ▁t ilt ▁west ward ▁with ▁height . ▁Cy c log en esis ▁is ▁most ▁likely ▁to ▁occur ▁in ▁regions ▁of ▁cycl onic ▁v ort icity ▁ad ve ction , ▁down stream ▁of ▁a ▁strong ▁w ester ly ▁jet . ▁The ▁combination ▁of ▁v ort icity ▁ad ve ction ▁and ▁thermal ▁ad ve ction ▁created ▁by ▁the ▁temperature ▁gradient ▁and ▁a ▁low ▁pressure ▁center ▁cause ▁up ward ▁motion ▁around ▁the ▁low . ▁ ▁If ▁the ▁temperature ▁gradient ▁is ▁strong ▁enough , ▁temperature ▁ad ve ction ▁will ▁increase , ▁driving ▁more ▁vertical ▁motion . ▁This ▁increases ▁the ▁overall ▁strength ▁of ▁the ▁system . ▁She ar wise ▁upd raft s ▁are ▁the ▁most ▁important ▁factor ▁in ▁determ ining ▁cycl onic ▁growth ▁and ▁strength . ▁ ▁M odes ▁of ▁development ▁ ▁A ▁surface ▁low ▁can ▁have ▁a ▁variety ▁of ▁causes ▁for ▁forming . ▁Top ography ▁can ▁force ▁a ▁surface ▁low ▁to ▁form ▁when ▁an ▁existing ▁bar oc lin ic ▁wave ▁moves ▁over ▁a ▁mountain ▁bar rier ; ▁this ▁is ▁known ▁as ▁" lee ▁cy c log en esis " ▁since ▁the ▁low ▁forms ▁on ▁the ▁le ew ard ▁side ▁of ▁the ▁mountains . ▁ ▁Mes osc ale ▁con ve ct ive ▁systems ▁can ▁spawn ▁surface ▁l ows ▁which ▁are ▁initially ▁warm ▁core . ▁ ▁The ▁disturb ance ▁can ▁grow ▁into ▁a ▁wave - like ▁formation ▁along ▁the ▁front ▁and ▁the ▁low ▁will ▁be