( Tornadoes ( ( can ( ( ( happen ( at ( ( ( ( any hour ) ( of ( the day ) ) ) and ) ( ( any time ) ( of ( the year ) ) ) ) ) ) , ) ( though ( they ( ( ( ( ( are ( ( most common ) ( in ( the spring ) ) ) ) , ) especially ) ( during ( ( May and ) June ) ) ) ( in ( North America ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Tornadoes)) (VP (MD can) (VP (VB happen) (PP (IN at) (NP (NP (NP (DT any) (NN hour)) (PP (IN of) (NP (DT the) (NN day)))) (CC and) (NP (NP (DT any) (NN time)) (PP (IN of) (NP (DT the) (NN year)))))) (, ,) (SBAR (IN though) (S (NP (PRP they)) (VP (VBP are) (ADJP (ADJP (RBS most) (JJ common)) (PP (IN in) (NP (DT the) (NN spring)))) (, ,) (ADVP (RB especially)) (PP (IN during) (NP (NNP May) (CC and) (NNP June))) (PP (IN in) (NP (NNP North) (NNP America)))))))) (. .)))
Tornadoes can happen at any hour of the day and any time of the year, though they are most common in the spring, especially during May and June in North America.
(ROOT (S (NP (NNS Tornadoes)) (VP (MD can) (VP (VB occur) (PP (IN in) (NP (DT any))))) (. .)))