Cold Fronts and Warm Fronts

Unlike seabreezes, cold fronts are active mainly during winter and come at any time of day or night.   Cold fronts pass through during the other months, but usually fall apart by the time they reach our area.  Like seabreezes, cold fronts cand range from simply making the sky cloudy to wicked storms with gusty winds.  Cold fronts, as the name suggests, is a line of cold air travelling along, generally west to east.  As this cold air meets warmer air, the warm air rises, and you guessed, causes the cold air to rush in and fill the space. Thus, the actual 'front' of the front, called the 'squall line' is generally where most of the wind is.

Because the winds travel clockwise around a low pressure system, the first taste you get is Northerly, but more often than not North Westerly.  As the cold front passes through these winds rotate around the compass, going from NW to W to SW, and maybe S.    The S part can get quite chilly because it dredging all the cool air from the antartic regions.   Not cold by UK standards, but enough to make your face numb.    North Easterlies on the other hand can be quite warm, relative to the usual winter temperatures.  The time it takes for the NW to SW transition depends on the speed at which the front is traveling.  Usually around a day, sometimes two.

Time to introduce another term - the pressure gradient.

Warm Fronts

A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fronts, and move more slowly than the cold fronts which usually follow because cold air is denser and less easy to remove from the Earth's surface.

This also forces temperature differences across warm fronts to be broader in scale.

Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue