air masses cold fronts, warm fronts, stationary fronts and occluded fronts

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  • Air MassesCold fronts, Warm fronts, Stationary fronts and Occluded fronts.

  • Fronts

    A front is defined as the transition zone between two air masses of different density. Fronts extend not only in the horizontal direction, but in the vertical as well. Therefore, when referring to the frontal surface (or frontal zone), we referring to both the horizontal and vertical components of the front.

    Stationary Front A front that is not moving. Cold Front Leading edge of colder air that is replacing warmer air. Warm Front Leading edge of warmer air that is replacing cooler air. Occluded Front When a cold front catches up to a warm front.

  • Cold FrontA cold front is defined as the transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour.

    Symbolically, a cold front is represented by a solid line with triangles along the front pointing towards the warmer air and in the direction of movement. On colored weather maps, a cold front is drawn with a solid blue line.

  • There is typically a noticeable temperature change from one side of a cold front to the other. In the map of surface temperatures below, the station east of the front reported a temperature of 55 degrees Fahrenheit while a short distance behind the front, the temperature decreased to 38 degrees. An abrupt temperature change over a short distance is a good indicator that a front is located somewhere in between.

  • Warm Front

    A warm front is defined as the transition zone where a warm air mass is replacing a cold air mass. Warm fronts generally move from southwest to northeast and the air behind a warm front is warmer and more moist than the air ahead of it. When a warm front passes through, the air becomes noticeably warmer and more humid than it was before. Symbolically, a warm front is represented by a solid line with semicircles pointing towards the colder air and in the direction of movement. On colored weather maps, a warm front is drawn with a solid red line.

  • If colder air is replacing warmer air, then the front should be analyzed as a cold front. On the other hand, if warmer air is replacing cold air, then the front should be analyzed as a warm front.

  • A developing cyclone typically has a preceding warm front (the leading edge of a warm moist air mass) and a faster moving cold front (the leading edge of a colder drier air mass wrapping around the storm). North of the warm front is a mass of cooler air that was in place before the storm even entered the region.

    Occluded Front

  • Occluded FrontAs the storm intensifies, the cold front rotates around the storm and catches the warm front. This forms an occluded front, which is the boundary that separates the new cold air mass (to the west) from the older cool air mass already in place north of the warm front.

    Symbolically, an occluded front is represented by a solid line with alternating triangles and circles pointing the direction the front is moving. On colored weather maps, an occluded front is drawn with a solid purple line.

  • Changes in temperature, dew point temperature, and wind direction can occur with the passage of an occluded front. In the map below, temperatures ahead (east of) the front were reported in the low 40's while temperatures behind (west of) the front were in the 20's and 30's. The lower dew point temperatures behind the front indicate the presence of drier air.

  • Stationary Front

    When a warm or cold front stops moving, it becomes a stationary front. Once this boundary resumes its forward motion, it once again becomes a warm front or cold front. A stationary front is represented by alternating blue and red lines with blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air.

  • Stationary FrontIn the map above, temperatures south of the stationary front were in the 50's and 60's with winds generally from the southeast. However, north of the stationary front, temperatures were in the 40's while the winds had shifted around to the northeast. Cyclones migrating along a stationary front can dump heavy amounts of precipitation, resulting in significant flooding along the front.

  • Answer these questions1. An area where air masses meet but do not mix is called a Front2. After a cold front moves through an area, cool dry air moves in, often bringing ______skies and ______temperatures.Clear and cooler

  • Answer these questions3. After a warm front passes through an area, the weather is likely to warm and ______.Humid

    4. Sometimes cold and warm air masses meet, but neither one has enough force to move the other. This is called a _______ front.Stationary

  • Answer these questions5. At a(n) _________front, a warm air mass is caught between two cooler air masses.Occluded

    6. The symbol for a cold front looks like;A. B. C.

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