( Tornadoes ( ( ( ( ( can ( appear ( ( any time ) ( of year ) ) ) ) , ) but ) ( are ( ( most common ) ( during ( the ( spring ( and ( summer months ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Tornadoes)) (VP (VP (MD can) (VP (VB appear) (NP (NP (DT any) (NN time)) (PP (IN of) (NP (NN year)))))) (, ,) (CC but) (VP (VBP are) (ADJP (ADJP (RBS most) (JJ common)) (PP (IN during) (NP (DT the) (NN spring) (CC and) (NN summer) (NNS months)))))) (. .)))
Tornadoes can appear any time of year, but are most common during the spring and summer months.
(ROOT (S (NP (NNS Tornadoes)) (VP (MD can) (VP (VB occur) (PP (IN in) (NP (DT any))))) (. .)))