chapter 20.2 fronts and lows objectives: -describe the weather conditions associated with...
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Chapter 20.2 Fronts and Lows
Objectives:-Describe the weather conditions
associated with different types of frontsDescribe the life cycle of a mid-latitude
low
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What is a Front?
The boundary that separates opposing air masses
Can be 5 km high and 2000 longAir masses on either side of a front may
differ in temperature and humidity
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Fronts con’t
Less dense air is forced to rise over denser air resulting in a wedge shape
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Types of Fronts
Cold FrontWarm FrontStationary FrontOccluded Front
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Types of Fronts – Cold Front
Boundary between an advancing cold air mass and the warmer air mass it is displacing
Cold air slides below Warm airThunderstorms often accompany cold
fronts if they replace humid mT air
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Cold Front:
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Types of Fronts – Warm Front
Boundary between advancing warm air mass and cold air mass it is displacing
First signs are wispy cirrus clouds
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Advancement of a Warm Front
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Types of Fronts – Occluded Front
Occurs when cold front catches up to warm front, forcing warm air to rise.
Results in clouds and precipitation
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Advancement of an Occluded Front
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Types of Fronts – Stationary Front
Front that does not move or moves very slowly
Can result in flooding if precipitation results from warm air rising
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Stationary Front
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Front Symbols
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Mid-Latitude Low
Mid-Latitude Cyclone
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Upper-Air Flow
Low Pressure systems are controlled (path and intensity) by upper air flow
See Diagram on pg 443
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Troughs and Ridges
Troughs – Upper level winds that slow, forcing air downward creating high pressure at the surface
Ridges – Upper level winds that spread out (diverge) causing surface air to rise, creating low pressure at the surface
Strengths of highs and lows are dependent upon how sharp the bend in upper air flow is
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High pressure areas (anticyclones) Clockwise airflow in the Northern Hemisphere (opposite flow direction in S. Hemisphere)
– Characterized by descending air which warms creating clear skies
Low pressure areas (cyclones) Counterclockwise airflow in N. Hemisphere (opposite flow in S. Hemisphere)
– Air converges toward low pressure centers, cyclones are characterized by ascending air which cools to form clouds and possibly precipitation
Anticyclones and Cyclones