In general, the theory and practice of surface synoptic chart analysis by the so- called Norwegian methods, which involve the concepts of the polar front and of the broad-scale air mass that it separates. Airmass analysis of surface charts may be said to consist of 1) determining the extent, the physical and stability properties, the movements, and the modifications of each of the air masses on the chart; 2) locating with some precision the fronts separating the air masses, and analyzing the structure and motion of the fronts; 3) analyzing wave perturbations on the fronts; and 4) describing and explaining the weather on the basis of the above factors.