An attempt is made to select a type series of constant-pressure charts associated with the life cycle of the pre-cold frontal instability line, especially over the southeastern States during the spring season. Emphasis is placed upon advective temperature changes that result in the development and maintenance of warm and cold tongues and the resultant elongated transitional zone in the fore part of the associated trough. The instability line develops along the axis of a warm tongue at 850 mb after cold air advection at 700 mb has reached the fore part of the associated trough and is advancing at a more rapid rate than the warm tongue.

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