( ( Snowstorms ( affecting ( Northeastern ( United States ) ) ) ) ( often ( ( ( get ( their moisture ) ) ( from ( air ( ( moving ( north ( from ( ( ( ( the Gulf ) ( of Mexico ) ) and ) ( ( cold air ) ( from ( air masses ) ) ) ) ) ) ) ( ( coming down ) ( from ( the Arctic ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (NP (NNS Snowstorms)) (VP (VBG affecting) (NP (NNP Northeastern) (NNP United) (NNPS States)))) (ADVP (RB often)) (VP (VBP get) (NP (PRP$ their) (NN moisture)) (PP (IN from) (NP (NP (NN air)) (VP (VBG moving) (ADVP (RB north) (PP (IN from) (NP (NP (NP (DT the) (NNP Gulf)) (PP (IN of) (NP (NNP Mexico)))) (CC and) (NP (NP (JJ cold) (NN air)) (PP (IN from) (NP (NN air) (NNS masses))))))) (S (VP (VBG coming) (PRT (RP down)) (PP (IN from) (NP (DT the) (NNP Arctic))))))))) (. .)))
Snowstorms affecting Northeastern United States often get their moisture from air moving north from the Gulf of Mexico and cold air from air masses coming down from the Arctic.
(ROOT (S (NP (NP (DT The) (JJS best) (NN explanation)) (PP (IN for) (SBAR (WHADVP (WRB how)) (S (NP (NN air) (NNS masses)) (VP (VBP move) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))))))) (VP (VBZ is) (SBAR (IN that) (S (NP (DT the) (VBG prevailing) (NNS westerlies)) (VP (VP (VBP move) (NP (NN air) (NNS masses)) (PP (IN from) (NP (NN west))) (PP (TO to) (ADJP (JJ east))) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))) (CC but) (VP (MD may) (VP (VB be) (VP (VBN deflected) (PP (IN by) (NP (DT the) (NN jet) (NN stream)))))))))) (. .)))