( ( ( Air ( Masses ( Warm ( Fronts ( and ( Cold ( Fronts ( High ( Pressure ( and ( Low ( Pressure ( Cyclones ( and ( Anticyclones ( Air Masses ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ( For ( ( a discussion ) ( of weather ) ) ) ) ( , ( it ( ( might ( be ( easiest ( to ( think ( in ( terms ( of ( air masses ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (NP (NNP Air) (NNP Masses) (NNP Warm) (NNPS Fronts) (CC and) (NNP Cold) (NNPS Fronts) (NNP High) (NNP Pressure) (CC and) (NNP Low) (NN Pressure) (NNP Cyclones) (CC and) (NNP Anticyclones) (NNP Air) (NNS Masses)) (IN For) (NP (NP (DT a) (NN discussion)) (PP (IN of) (NP (NN weather))))) (, ,) (NP (PRP it)) (VP (MD might) (VP (VB be) (ADJP (JJ easiest) (S (VP (TO to) (VP (VB think) (PP (IN in) (NP (NP (NNS terms)) (PP (IN of) (NP (NN air) (NNS masses))))))))))) (. .)))
Air Masses Warm Fronts and Cold Fronts High Pressure and Low Pressure Cyclones and Anticyclones Air Masses For a discussion of weather, it might be easiest to think in terms of air masses.
(ROOT (S (PP (IN In) (NP (NN weather) (NNS terms))) (, ,) (NP (NP (DT the) (NN boundary)) (PP (IN between) (NP (CD two) (NN air) (NNS masses)))) (VP (VBZ is) (VP (VBN called) (NP (NN front)))) (. .)))
In weather terms, the boundary between two air masses is called front.