Cold Front - Development of Cold Front

Development of Cold Front

The cooler and denser air wedges under the less-dense warmer air, lifting it. This upward motion causes lowered pressure along the cold front and can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel. A cold front's location is at the leading edge of the temperature drop off, which in an isotherm analysis would show up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts move faster than warm fronts and can produce sharper changes in weather. Since cold air is denser than warm air, it rapidly replaces the warm air preceding the boundary.

In the northern hemisphere, a cold front usually causes a shift of wind from southwest to northwest clockwise, also known as veering, and in the southern hemisphere a shift from northeast to southwest, in a clockwise manner. Normally, cold fronts can be marked by these characteristics:

Weather phenomenon	Prior to the Passing of the Front	While the Front is Passing	After the Passing of the Front
Temperature	Warm	Cooling suddenly	Steadily cooling
Atmospheric pressure	Decreasing steadily	Lowest, then sudden increase	Increasing steadily
Winds	Southwest to southeast (northern hemisphere) Northwest to northeast (southern hemisphere)	Gusty; shifting	North to west, usually northwest (northern hemisphere) South to west, usually southwest (southern hemisphere)
Precipitation/conditions*	Light patchy rain can be produced by stratocumulus or stratus in the warm sector.	Prolonged rain (nimbostratus) or thunderstorms (cumulonimbus): depends on conditions.	Showers, then clearing
Clouds*	Usually takes the form of a line of cumulonimbus and/or cumulus congestus clouds, but can also be nimbostratus or stratus/stratocumulus if the front is weak. Approach often obscured by stratocumulus or stratus in the warmer air approaching it, but if the air is clear usually a small sharply edged altostratus sheet can be seen marking the edge of the approaching front.	Cumulonimbus or nimbostratus	Patchy altocumulus and altostratus along with stratus fractus then cumulus and cumulonimbus
Visibility*	Fair to poor in haze	Poor, but improving	Good, except in showers
Dew Point	High; steady	Sudden drop	Falling

*Provided there is sufficient moisture.

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