Weather Fronts and Mid-latitude Lows May 20, 2008
Front • A front is the boundary that separates opposing air masses. • Fronts are most common at mid-latitudes where southward-moving polar air masses and northward-moving tropical air masses often meet.
Cold Front • A cold front is the boundary between and advancing cold air mass and the warmer air mass it is displacing.
Warm Front • When warm air displaces cold air the boundary between the air masses is a warm front.
Occluded Front • Occluded front is the front that is formed when a cold front overtakes a warm front and displaces it upward in an area of low pressure.
Mid-Latitude Low Formation • Fronts are usually connected to mid-latitude low-pressure systems. • A low pressure system often starts out as a small ripple on a stationary polar front where cold polar air meets warm tropical air.
Norwegian Model • A wave on the front will form as an upper level disturbance embedded in the jet stream moves over the front. The front develops a "kink" where the wave is developing. • Precipitation will begin to develop with the heaviest occurrence along the front (dark green).
Norwegian Model • Winds blow counterclockwise around the low. • As the wave intensifies, both cold and warm fronts become better organized.
Norwegian Model • The wave becomes a mature low pressure system, while the cold front, moving faster than the warm front, "catches up" with the warm front. As the cold front overtakes the warm front, an occluded front forms.
Norwegian Model • As the cold front continues advancing on the warm front, the occlusion increases and eventually cuts off the supply of warm moist air, causing the low pressure system to gradually dissipate.
Visualizing a Mid-Latitude Storm System • Would putting the steps together you have learned be easier with an animation? • Animated Link
Homework • Fronts Assignment