Weather Fronts

Introduction

• Definition: Borders between different weather systems
• Significance: Indicate upcoming weather changes
• Types: Warm fronts, cold fronts, occluded fronts

Warm Fronts

• **Characteristics:
  • Warm air moves into colder air area
  • Represented with red semicircles on maps
  • Slopes up towards colder air (1:150 ratio)
  • Length: Typically 600-700 nautical miles
  • Travels at 1/3 speed of 2000-foot wind
• Weather Conditions:
  • Gradual ascension of warm air
  • Produces stratiform weather (cirrus, altostratus, nimbostratus, stratus clouds)**

Cold Fronts

• **Characteristics:
  • Cold air forces its way under warmer air
  • Represented with blue icicles on maps
  • Slopes up steeper than warm fronts (1:50 ratio)
  • Length: Typically 100 nautical miles
  • Travels at 2/3 speed of 2000-foot wind
• Weather Conditions:
  • Rapid ascension of warm air
  • Produces cumuliform weather (cumulonimbus, cumulus, altocumulus clouds)
  • Can result in gusty wind conditions**

Occluded Fronts

• Definition: When a cold front catches up to a warm front
• Characteristics:
  • Forms a "V" shape with warm air sandwiched between cold air masses
  • Associated with wet weather

Pressure Changes

• Warm Fronts:
  • As it approaches, pressure drops gradually due to warm, less dense air.
• Cold Fronts:
  • As it passes, pressure increases rapidly due to cold, more dense air.

Global Frontal Zones

• Polar Front:
  • Boundary between tropical & polar maritime air masses
  • Moves north and south with seasons
• Intertropical Convergence Zone (ITCZ):
  • Formed near the equator
  • Hot air rises causing low pressure, air descends back to earth at tropics creating high pressure
  • Creates trade winds

Polar Front Depression

• Formation: Warm air bulges into cold air, wind curves around bulge forming low pressure
• Characteristics:
  • Warm air moves northeast, cold air moves southeast
  • Associated with mixed weather conditions (warm, humid in warm sector; thunderstorms, heavy rain at cold front)
• Impact: Frequent in Europe, leads to consistent rain and storms

Thermal Depressions

• Formation: Surface heating causes air to rise, creating low pressure (common in summer)
• Extreme Form: Tropical revolving storms (hurricanes, cyclones, typhoons)
  • Occur in specific regions due to warm oceans and seasons
  • Causes severe weather conditions (violent winds, rainfall)

Summary

• Warm fronts: Move slowly, produce stratiform weather, gradual pressure drop
• Cold fronts: Move faster, produce cumuliform weather, rapid pressure rise
• Occluded fronts: Mix of warm and cool front conditions
• Global frontal zones: Polar front, ITCZ
• Polar front depressions: Mixed weather, frequent in Europe
• Thermal depressions: Related to surface heating, extreme form leads to hurricanes/typhoons/cyclones