Lecture: Severe Weather and Air Masses

Introduction to Air Masses

• Definition: A large body of air with uniform moisture/humidity and temperature characteristics across a broad geographic area.
• Classification: Air masses must be similar in attributes over a horizontal distance, not just isolated pockets of air.
• Size: Must cover a few hundred miles to be considered an air mass. Urban areas with significant topography are not suitable for air mass formation.

Characteristics and Formation

• Source Regions: Large, flat areas with similar temperature and moisture characteristics.
  • Example regions: Central Canada, Central Russia (Siberia).
• Requirement: Consistent conditions, absence of significant wind patterns, and flat terrains.
• High-Pressure Zones: Ideal for air mass development due to descending air, e.g., subtropical highs.
• Types: Cold dry air forms over land; warm moist air forms over large bodies of water, like the Gulf of Mexico.

Factors Influencing Air Mass Changes

• Movement: Wind can move air masses, changing their characteristics as they pass over different terrains.
• Speed and Distance: Faster-moving air masses change more quickly; the farther they travel, the more they change.
• Difference in Regions: The more different the new region is from the source region, the greater the change in the air mass.

Labeling Air Masses

• Formation: Over land (Continental, C) or water (Maritime, M).
• Temperature: Polar (P), Arctic (A), Tropical (T), Equatorial (E).

Specific Designations

• North America Impact: CP and CA Air Masses
  • Continental Polar (CP): Dry air from Canada and Alaska, cold but not extremely cold.
  • Continental Arctic (CA): Extremely cold and dry, forming further north than CP.
• Maritime Air Masses:
  • Maritime Polar (MP): Formed over northern Pacific or Atlantic, cold and moist.
  • Maritime Tropical (MT): Warm and humid, forming over warm ocean waters like the Gulf of Mexico or East Pacific.
• Continental Tropical (CT):
  • Hot and dry, forming over land in regions like West Texas (e.g., Sonoran Desert).

Impact on Weather Patterns

• Interaction and Severe Weather: Understanding how different air masses interact is key to forecasting severe weather events.
• Precipitation Patterns:
  • MP air masses influence the Pacific Northwest through orographic effects, leading to more precipitation on windward sides of mountains and arid conditions on leeward sides (rain shadow effect).
  • MT air masses bring high humidity and warm weather to areas like the southeastern USA, impacting daily weather significantly.

Summary

• Air masses are large, homogeneous bodies of air categorized based on their temperature, moisture, and place of origin.
• Understanding air masses and their movement is crucial for predicting weather patterns and severe weather.
• Next, the course will cover how air masses interact to cause severe weather.