How do fronts work

Weather fronts are the result of air masses , large bodies of air of similar temperature and humidity across any horizontal direction.

Air masses are formed when air stagnates over a uniform surface for a significant period of time. Air masses can extend hundreds, or even thousands, of miles horizontally. Meteorologists differentiate between continental air masses which form over land and maritime air masses, which originate over the ocean.

Continental air masses are dry air masses; maritime air masses are moist. Then, air masses are further delineated based on the temperature of the surface over which they originate.

These classifications include:. Air masses change as they move around Earth. Air masses impact offshore weather forecasts, but their effect can sometimes be difficult to understand — until now. What do all these different factors mean for offshore weather forecasts? Understanding how air masses form and move around the planet can help the shipping industry, fishing industry, and coastal communities prepare for bad weather. The weather may be cold and clear or only partly cloudy.

Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Along a warm front , a warm air mass slides over a cold air mass. When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching.

The transition from cold air to warm air takes place over a long distance so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other.

Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that.

The weather worsens. Cold fronts can be associated with squall lines a line of strong thunderstorms parallel to and ahead of the front. In winter, cold fronts move into Oklahoma mainly from the Canadian prairies but sometimes from the Arctic Circle or the eastern Pacific. Cold fronts almost always are easier to locate on a weather map than are warm fronts, primarily because of the strength of the high pressure system to the north and west of the cold front compared to that north of a warm front.

Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction. Warm Fronts. Warm front- a front in which warm air replaces cooler air at the surface. Some of the characteristics of warm fronts include the following: The slope of a typical warm front is more gentle than cold fronts.

Warm fronts tend to move slowly. Warm fronts are typically less violent than cold fronts. Although they can trigger thunderstorms, warm fronts are more likely to be associated with large regions of gentle ascent stratiform clouds and light to moderate continuous rain. Warm fronts are usually preceded by cirrus first km ahead , then altostratus or altocumulus km ahead , then stratus and possibly fog.

Behind the warm front, skies are relatively clear but change gradually. A cold front is more dangerous, as it often brings squally winds, thunderstorms and rains. As a rule, such bad weather comes suddenly, but it does not last long: a cold front moves rather quickly — up to 80 kilometers per hour. In the Northern Hemisphere, such fronts usually move from northwest to southeast, in the Southern Hemisphere - from southwest to northeast.

A warm front can also bring bad weather, but the rains can last the whole day or more, because its precipitation zone is much wider, and also it moves much slower than the cold one — kilometers per hour or less. Wind increase in a warm front is not as strong as in a cold front. In the Northern Hemisphere, warm fronts usually move from southwest to northeast, in the Southern Hemisphere — from northwest to southeast.

The surface of the front is always sloping against the ground. In the case of a cold front, cold air jumps under warm air, forcing it to rise up. In a warm front, warm air still rises up, but gradually squeezes out the cold air underneath.

The behavior of cold and warm air in fronts. Above is the movement of a cold front, below - that of a warm one.