Weather

What is Weather?

• Definition: The short-term condition of the atmosphere (current state).

• Cause: Differential Heating.
    - The Sun heats Earth unevenly.
      - Land heats faster than water.
      - The Equator heats more than the poles.

• Chain Reaction: Uneven Heat → Density Differences → Pressure Differences → Wind.

• Concept Breakdown:
    - Distinguish between "Weather" (short-term) and "Climate" (long-term).
    - The sun is the engine for all weather because it heats the Earth unevenly.

Meteorological Instruments

• Thermometer: Measures Temperature.

• Barometer: Measures Air Pressure (falling pressure indicates storm).

• Wind Vane: Measures Wind Direction.

• Anemometer: Measures Wind Speed (cups spin).

• Psychrometer/Hygrometer: Measures Relative Humidity and Dew Point.

Advanced Instruments

• Concept Breakdown (Basics):
    - Standard tools essential for everyday weather prediction.
    - Focus on the Barometer - crucial for forecasting (pressure changes indicate upcoming weather).

• Concept Breakdown (Advanced):
    - A psychrometer uses two thermometers (wet and dry) to assess evaporation.
    - Higher evaporation correlates with drier air.

Understanding Air Density

• Warm Air:
    - Molecules spread out → Low Density → Rises.

• Cold Air:
    - Molecules pack tightly → High Density → Sinks.

• Concept Breakdown:
    - Conceptualize using a hot air balloon: Hot air is less dense and rises while cold air is denser and sinks.

Understanding Air Pressure

• Definition: The weight of the air pushing down.

• Measurement: Measured with a Barometer.

• Unit: Millibars (mb).

• Standard Pressure: Sea level is approximately 1013 mb.

• Concept Breakdown:
    - Air has mass; pressure results from the weight of the atmosphere.

The Engine: Convection Cells

• Definition: A loop of moving air.

• The Cycle:
    1. Warm air rises.
    2. It cools.
    3. It sinks.
    4. Flows back to the start.

• Concept Breakdown:
    - Circular motion forms the foundation for all wind and storms. Understanding convection means understanding weather.

Specific Heat Capacity

• Concept: The speed at which a substance heats up or cools down.
    - Water: High specific heat (heats and cools slowly).
    - Land: Low specific heat (heats and cools quickly).

• Example: On a hot day, sand heats faster than water, illustrating the differences in specific heat capacity.

Local Winds: Sea Breeze

• Time & Conditions: Daytime.
    - Land heats up leading to Low Pressure.
    - The ocean remains cooler creating High Pressure.

• Result: Wind blows from Ocean to Land.

• Concept Breakdown: Wind direction is dictated by pressure differences; it always flows from High to Low Pressure.

Local Winds: Land Breeze

• Time: Night time.

• Conditions:
    - Land cools fast → High Pressure.
    - Ocean stays warm → Low Pressure.

• Result: Wind blows from Land to Ocean.

• Concept Breakdown: At night, cooler land creates reversal in wind direction.

The Essential Ingredient: Condensation Nuclei

• Requirement: Water vapor needs a surface to condense upon.

• Examples: Dust, salt, smoke particles act as condensation nuclei.

• Function: These particles are essential for rain to form; without them, water vapor cannot condense into droplets.

The Dew Point

• Definition: The temperature where air becomes 100% saturated with water vapor.

• Rule: If Air Temperature equals Dew Point, clouds or fog form.

• Concept Breakdown: The Dew Point serves as a target temperature; when the air cools down to this point, condensation occurs, leading to cloud formation.

Cloud Formation: The Recipe

• Process: Adiabatic Cooling.
    1. Warm air rises, expands and cools.
    2. It reaches the Dew Point, resulting in cloud formation.

• Concept Breakdown: Memorize the process as "Rise, Expand, Cool, Condense". These steps are essential for understanding natural cloud formation.

Precipitation Types

Part 1: Basic Forms

• Rain: Liquid drops falling through warm air.

• Snow: Ice crystals falling through freezing air.
    - Distinction: Rain occurs when air column temperatures are warm; snow occurs when temperatures are below freezing.

Part 2: Sleet and Freezing Rain

• Sleet: Raindrops freeze into ice pellets before hitting the ground.

• Freezing Rain: Rain that freezes on contact with cold surfaces.
    - Danger: Freezing rain creates glaze ice, hazardous for travel.

• Concept Breakdown: The key difference is the timing of freezing: Sleet freezes in the air whereas freezing rain freezes upon contact.

The Station Model

• Definition: A symbol used by meteorologists to summarize weather data at a location.

• Components:
    - Contains data on temperature, pressure, humidity, cloud cover, and wind direction/speed.

• Concept Breakdown: Acts like a summary dashboard of weather conditions.

Reading a Station Model (Components)

Temperature and Dew Point

• Temperature: Located at the top left (typically in Fahrenheit).

• Dew Point: Placed below temperature.

Cloud Cover

• Visual Representation: Illustrated by the circle within the model; its filling indicates cloud cover.

Reading a Station Model (Wind)

• Wind Direction: Indicated by the stick (wind barb) pointing from where the wind is coming.

• Wind Speed: Determined by counting barbs (half barb = 5 knots, full barb = 10 knots, pennant = 50 knots).

Reading a Station Model (Pressure)

• Air Pressure: Located at the top right.

• Coded Pressure: Requires conversion to determine actual pressure.

• Concept Breakdown: Rising pressure generally indicates clear weather, while falling pressure often signifies an incoming storm.

Converting Coded Pressure to Actual Pressure

• Rules:
    - If coded number ≥ 500, add "9" in front and place a decimal before the last digit.
    - If coded number < 500, add "10" in front and place a decimal before the last digit.

• Example: Coded pressure 864 results in actual pressure: 986.4 mb.

Reasoning Rule (Regents-Style)

• Comparison: Examine the relationship between Temperature and Dew Point.
    - If temperature is close to Dew Point, it suggests high humidity and the potential for precipitation.

• Example: A small gap between temperature and Dew Point indicates humid conditions whereas a large gap suggests dry air.

Global Circulation (The Big Picture)

• Coriolis Effect: Due to Earth's rotation, winds do not travel in straight lines; they curve right in the Northern Hemisphere.

• Jet Stream: High-altitude winds that guide weather patterns, pushing storms from west to east.

• Concept Breakdown: Understanding these principles is crucial for predicting large-scale weather systems.

Air Masses

• Definition: A large body of air with uniform temperature and moisture.

• Naming Rule: Named by their source region; e.g. maritime polar (mP) for cool and humid air from oceans, continental tropical (cT) for hot and dry air from land.

Frontal Systems: The Battles of Air Masses

Types of Fronts

• Cold Front:
    - Action: Cold air moves in quickly, pushing warm air upwards; leads to thunderstorms followed by cooler, drier weather.

• Warm Front:
    - Action: Warm air gently slides over cold air; leads to steady precipitation.

• Stationary Front: Neither air mass moves, resulting in prolonged rain.

• Occluded Front: A fast cold front displaces warm air entirely.

Mid-Latitude Cyclones

• Definition: Standard storm systems in the US.

• Characteristics: Winds blow inward and counterclockwise around a low-pressure center.

Life Cycle of a Cyclone

1. Formation: A front forms between cold and warm air.

2. Spin: Pressure drops, initiating the rotation.

3. Maturity: The storm evolves with warm sectors bringing rain and cold fronts brining storms.

Isobars and Wind

• Isobars: Lines connecting points of equal pressure on a weather map.

• Importance: Spacing of isobars indicates wind strength; close lines signal strong winds while wide spacing corresponds with light winds.

High vs. Low Pressure Systems

• High (H): Results in sinking air, leading to clear, dry weather; rotates clockwise.

• Low (L): Rising air results in cloudy, wet weather; rotates counterclockwise.

Forecasting with Fronts

• Cold Front Rule: Look for a narrow band of heavy precipitation and thunderstorms.

• Warm Front Rule: Identify widespread clouds and steady precipitation.

• Stationary/Occluded Rule: Watch for persistent overcast conditions.

Analyzing Weather Maps

1. Identify high (H) and low (L) pressure areas.

2. Draw arrows showing wind directions around these pressure areas.

3. Circle areas near the fronts to highlight potential precipitation.

Radar vs. Satellite

• Radar: Shows precipitation intensity and likelihood of rain/snow.

• Satellite: Observes cloud patterns and storm structures.

Defining Natural Hazards

• Natural Event vs. Natural Hazard:
    - Example: A hurricane over the ocean is a natural event; it becomes a hazard when it threatens human life or property.

• Goal: Mitigation is essential to reduce damage from natural hazards.

Thunderstorms: The Ingredients

• Definition: Storms generating lightning and thunder.
    - Ingredients: Moisture, instability, and lift (like cold fronts). Each is crucial for storm formation.

How Lightning is Made

1. Charge Separation: Opposite charges build in the cloud.

2. Stepped Leader & Upward Streamer: Charges create a path for electrical discharge.

3. Return Stroke: The visible flash of lightning.

Thunder Formation

• Rapid Heating & Expansion: Caused by the intense heat from lightning, leading to a shockwave and the sound of thunder.

Storm Hazards

• Lightning: Dangerous electrostatic discharge.

• Hail: Formed through strong updrafts lifting raindrops into freezing air.

• Downbursts: Sudden powerful winds, potentially damaging.

Tornadoes (The Vortex)

• Definition: Violently rotating columns of air extending from clouds to the ground.

• Supercells: Large, rotating thunderstorms that generate strong tornadoes.

Tornado Alley

• Definition: Region in the U.S. known for frequent tornadoes.
    - Location: Includes Texas, Oklahoma, Kansas, Nebraska, South Dakota; formed by colliding warm, moist and cold, dry air masses.

Enhanced Fujita (EF) Scale

• Definition: Measures tornado intensity based on damage caused.

• Scale: Ranges from EF0 (65-85 mph) to EF5 (>200 mph) signifying increasing damage potential.

Tornado Safety

• Actions: Move to a basement or interior room, protect yourself from glass and debris, escape outdoor areas if possible.

Hurricanes (The Giants)

• Definition: Massive storm systems driven by warm ocean water, classified as tropical cyclones.

Hurricane Path & Behavior

• Typical Path: Forms off Africa, travels west/northwest, curves toward 30°N latitude before making landfall.

Category Wind Speed Measurement (Saffir-Simpson Scale)

• Scale Breakdown:
    - Cat 1: 74-95 mph (Minor Damage)
    - Cat 2: 96-110 mph (Moderate Damage)
    - Cat 3: 111-129 mph (Severe Damage)
    - Cat 4: 130-156 mph (Catastrophic Damage)
    - Cat 5: >157 mph (Total Destruction)

Case Study: Hurricane Sandy

• Notable Factors: Unusual late-season timing, interaction with cold fronts led to expansion and intensity.

• Catastrophic Impact: Significant flooding, power outages, high economic damage due to storm surge and peculiar path.

Winter Hazards

• Lake-Effect Snow: Cold air over warm lakes leads to heavy snow on downwind shores.

• Blizzard: High winds and low visibility criteria for classification.

Urban Heat Island Effect

• Concept: Cities have higher temperatures than rural areas due to heat-absorbing materials (like concrete) and reduced vegetation.

Drought Types

• Permanent and Seasonal Droughts: Classified by duration and conditions; the silent threat to agriculture and ecology.

Dust Bowl Case Study

• Event: Catastrophic disaster of the 1930s combining severe drought and poor agriculture leading to significant loss of soil and habitat.

Geologic Hazards: Earthquakes

• Definition: Ground shaking caused by fault movement.

• Mitigation: Employ ductility in construction to withstand seismic vibrations.

Geologic Hazards: Volcanoes

• Definition: Eruptions cause significant destruction; pyroclastic flows are particularly dangerous due to high speed and temperature.

Review Safety Measures

• Weather Safety: Guidelines for thunderstorms, hurricanes, tornadoes, and earthquakes focused on proactive planning and safety.