Decoding Guide

Standard Front Symbology

A front is defined as the transition zone between two air masses of different density. The following symbols have been designated to represent various types of fronts on standardized weather maps.
Representation Line Type of Front Definition
 Front Cold Front Transition zone where a cold air mass is replacing a warmer air mass.
Front Warm Front Transition zone where a warm air mass is replacing a cold air mass
Front Stationary Front When a warm or cold front stops moving, it becomes a stationary front
 Front Occluded Front When a cold front catches up to a warm front.
 Front Instability (Squall) Line Squall line storms consist of a line of storms with a continuous, well developed gust front at the leading edge of the line.
 Front Trough When pressure height contours bend strongly to the south. Strong troughs are typically preceded by stormy weather and colder air at the surface.
 Front Ridge When pressure height contours bend strongly to the north. Strong ridges are accompanied by warm and dry weather conditions at the surface.

A three digit frontal code is found along the side of the analyzed front. The first digit represents the type of front, the second the frontal intensity, and the third the frontal character. The three digits are preceded or followed by a bracket, [ ].

First Digit-Type of Front Second Digit - Frontal Intensity Third Digit - Frontal Character
0 : Quasi-stationary
1: Quasi-stationary front above the surface
2: Warm front at the surface
3: Warm front above the surface
4: Cold front at the surface
5: Cold front above the surface
6: Occluded front
7: Instability Line
8: Intertropical front
9: Converge Line
0: Not specified
1: Weak and Decreasing
2: Weak and little change
3: Weak and increasing
4: Moderate and decreasing
5: Moderate and little change
6: Moderate and increasing
7: Strong and decreasing
8: Strong and little change
9: Strong and increasing
0: Not specified
1: Frontal activity area decreasing
2: Frontal activity area show little change
3: Frontal activity area increasing
4: Intertropical
5: Forming or existence expected
6: Quasi-stationary
7: with waves
8: Diffuse
9: Position doubtful