Improved Study Notes on Climate and Weather in the United States

Physical Geography of the United States II – Climate (Improved Study Notes)

Weather vs Climate

• Weather:
    - Defined as short-term atmospheric conditions at a specific time and place.
    - Includes factors such as:
      - Temperature
      - Precipitation
      - Wind
      - Storms

• Climate:
    - Defined as the long-term average weather patterns of a region, measured over decades.
    - Crucial for explaining large regional environmental differences across the United States.

Major Factors Affecting Climate

1. Latitude
      - Measures the distance north or south of the equator.
      - Solar energy decreases with increasing latitude, leading to cooler climates toward the poles.
      - Earth's axial tilt relative to the sun produces seasonal variations in temperature and daylight.

2. Proximity to Large Bodies of Water
      - Continentality:
        - Inland areas experience larger seasonal temperature variations.
      - Marine influence:
        - Coastal areas have milder temperatures due to the slow heating and cooling of water.
      - Ocean currents:
        - Transport warm or cold water, affecting nearby climates.
      - Proximity to water increases humidity and precipitation.

3. Topography (Elevation)
      - Higher elevations generally experience cooler temperatures.
      - Orographic precipitation:
        - Occurs when moist air rises over mountains, cools, and releases precipitation on the windward slopes.
        - Example: The Pacific Northwest receives heavy precipitation due to mountainous terrain near the Pacific Ocean.
      - Rain shadow:
        - Dry conditions occur on the leeward side of mountains after moisture has been lost.
        - Rain shadow effects lead to dry climates in many Intermontane regions.

Major Climate Regions of the United States

1. Humid Subtropical
      - Located in the southeastern United States.
      - Characterized by:
        - Short mild winters
        - Long hot and humid summers
        - Year-round precipitation with a maximum often occurring in autumn.
      - Example cities: Miami (FL), Dallas (TX), Nashville (TN).

2. Humid Continental
      - Occurs mainly north of about 35° latitude.
      - Features:
        - Warm summers and cold winters
        - Convergence of tropical air masses from the south with polar air masses from the north, leading to storms and severe weather.

3. Steppe (Semi-Arid)
      - Found in the Great Plains and northern Intermontane regions.
      - Characterized by:
        - Semi-arid climate with limited precipitation
        - Large seasonal temperature extremes
        - Prone to severe weather, including thunderstorms and tornadoes.

4. Desert
      - Located in the southwestern interior of the United States.
      - Characterized by:
        - Extremely dry climate with minimal precipitation
        - Very hot summers with warm autumn temperatures
        - Santa Ana Winds: Hot, dry winds affecting southern California in autumn, increasing wildfire risk.

5. Mediterranean
      - Located in central and coastal California.
      - Characterized by:
        - Wet winters and dry summers
        - Marine influence keeps temperatures relatively mild along the coast.
        - Interior areas experience hotter summers and cooler winters.
        - The climate supports significant agricultural production.

6. Marine West Coast
      - Located in the Pacific Northwest.
      - Features:
        - Long, mild, and very wet winters
        - Short, relatively dry summers
        - Heavy precipitation caused by moist Pacific air.

7. Highlands
      - Found in mountainous regions, such as the Rocky Mountains and Sierra Nevada.
      - Climate is strongly influenced by:
        - Elevation and slope exposure
        - Higher elevations tend to be colder and may receive more precipitation.

Severe Weather in the United States

1. Hurricanes
      - Occur mainly in late summer and autumn.
      - Primarily impact the southeastern Atlantic and Gulf coasts.
      - Impact assessed by storm strength, fatalities, and economic damage.
      - Recent decades have seen stronger and more damaging storms.

2. Tornadoes
      - Most common in spring and early summer, particularly in the Great Plains known as Tornado Alley.
      - Form when warm moist air from the Gulf of Mexico meets cool dry air from the north.

3. Nor’Easters
      - Major winter storms affecting the northeastern U.S. coastline.
      - Can produce heavy precipitation, blizzards, coastal flooding, and strong winds.

4. Heat Index Events
      - Extreme heat events often affect large metropolitan areas, making urban populations, especially low-income communities, particularly vulnerable.

5. Severe Thunderstorms & Hail
      - Commonly occur in the Great Plains.
      - Result from the mixing of warm moist southern air with cooler northern air masses.

Climate Change

• Indicators:
    - Temperature changes
    - Alterations in precipitation patterns
    - Increase in extreme weather events.

• Causes:
    - Natural climate variability
    - Human activities, especially greenhouse gas emissions.

Potential Impacts of Climate Change

• Drought

• Coastal flooding

• More severe weather events

• Wildfires and worsening air pollution

• Changes to plant and animal behavior

• Human health impacts

• Changes to food production and availability

Key Takeaways

• Climate patterns in the U.S. are primarily shaped by:
    - Latitude
    - Proximity to water
    - Topography.

• Seven major climate regions classify regional climate differences.

• Severe weather hazards like hurricanes and tornadoes are closely linked to these climate patterns.

• Climate change is significantly influencing trends in temperature, precipitation, and the frequency of extreme weather events.