Weather front

A weather front is a boundary separating air masses of several characteristics such as air density, wind, temperature and humidity. Disturbed and unstable weather often arises from these differences. For instance, cold fronts can bring bands of thunderstorms and cumulonimbus precipitation or be preceded by squall lines, while warm fronts are usually preceded by stratiform precipitation and fog. In summer, subtler humidity gradients known as dry lines can trigger severe weather. Some fronts produce no precipitation and little cloudiness, although there is invariably always a wind shift.[1]

Approaching weather fronts are often visible from the ground, but are not always as well defined as this.

Cold fronts generally move from west to east, whereas warm fronts move poleward, however any is possible. Occluded fronts are a hybrid merge of the two, and stationary fronts are stalled in their motion. Cold fronts and cold occlusions move faster than warm fronts and warm occlusions, because the dense air behind them can lift as well as push the warmer air. Mountains and bodies of water can affect the movement and properties of fronts, other than atmospheric conditions.[2] When the density contrast has diminished between the airmasses, for instance after flowing out over a uniformly warm ocean, the front can degenerate into a mere line which separates regions of differing wind velocity known as a shearline. This is most common over the open ocean.

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