( ( ( ( ( Tornadoes ( ( are ( ( ( ( most common ) ( in spring ) ) and ) ( least common ) ) ) ( in winter ) ) ) , ) but ) ( tornadoes ( can ( ( occur ( ( any time ) ( of year ) ) ) ( that ( ( favorable conditions ) occur ) ) ) ) ) ) . )
(ROOT (S (S (NP (NNS Tornadoes)) (VP (VBP are) (ADJP (ADJP (ADJP (RBS most) (JJ common)) (PP (IN in) (NP (NN spring)))) (CC and) (ADJP (RBS least) (JJ common))) (PP (IN in) (NP (NN winter))))) (, ,) (CC but) (S (NP (NNS tornadoes)) (VP (MD can) (VP (VB occur) (NP (NP (DT any) (NN time)) (PP (IN of) (NP (NN year)))) (SBAR (IN that) (S (NP (JJ favorable) (NNS conditions)) (VP (VBP occur))))))) (. .)))
Tornadoes are most common in spring and least common in winter, but tornadoes can occur any time of year that favorable conditions occur.
(ROOT (S (NP (NNS Tornadoes)) (VP (MD can) (VP (VB occur) (PP (IN in) (NP (DT any))))) (. .)))