<P> When stationary fronts become smaller in scale, degenerating to a narrow zone where wind direction changes significantly over a relatively short distance, they become known as shearlines . A shearline is depicted as a line of red dots and dashes . Stationary fronts may bring snow or rain for a long period of time . </P> <P> A similar phenomenon to a weather front is the dry line, which is the boundary between air masses with significant moisture differences . When the westerlies increase on the north side of surface highs, areas of lowered pressure will form downwind of north--south oriented mountain chains, leading to the formation of a lee trough . Near the surface during daylight hours, warm moist air is denser than dry air of greater temperature, and thus the warm moist air wedges under the drier air like a cold front . At higher altitudes, the warm moist air is less dense than the dry air and the boundary slope reverses . In the vicinity of the reversal aloft, severe weather is possible, especially when a triple point is formed with a cold front . A weaker form of the dry line seen more commonly is the lee trough, which displays weaker differences in moisture . When moisture pools along the boundary during the warm season, it can be the focus of diurnal thunderstorms . </P> <P> The dry line may occur anywhere on earth in regions intermediate between desert areas and warm seas . The southern plains west of the Mississippi River in the United States are a particularly favored location . The dry line normally moves eastward during the day and westward at night . A dry line is depicted on National Weather Service (NWS) surface analyses as an orange line with scallops facing into the moist sector . Dry lines are one of the few surface fronts where the pips indicated do not necessarily reflect the direction of motion . </P> <P> Organized areas of thunderstorm activity not only reinforce pre-existing frontal zones, but can outrun cold fronts in a pattern where the upper level jet splits apart into two streams, with the resultant Mesoscale Convective System (MCS) forming at the point of the upper level split in the wind pattern running southeast into the warm sector parallel to low - level thickness lines . When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise . Even weaker and less organized areas of thunderstorms lead to locally cooler air and higher pressures, and outflow boundaries exist ahead of this type of activity, which can act as foci for additional thunderstorm activity later in the day . </P>

Identify the four types of fronts and the weather conditions associated with each one