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Predict Weather
Patterns

Learn to use observable evidence and atmospheric data to make probabilistic predictions about short-term weather changes.

Earth & Space Science

What Is Weather?

Weather describes the current state of the atmosphere at a specific place and time. It changes hour to hour and day to day, driven by energy from the Sun, moisture in the air, and differences in air pressure.

Temperature
How warm or cool the air is, measured in degrees.
Humidity
The amount of water vapor present in the air.
Air Pressure
The weight of the atmosphere pressing down at a given point.

Key Weather Variables

Temperature Thermometer Air Pressure Barometer Humidity Hygrometer Wind Anemometer

Why Probabilistic Predictions?

Weather is a chaotic system: tiny differences in starting conditions can lead to very different outcomes. That is why forecasts are expressed as probabilities rather than certainties.

The further ahead we forecast, the less certain the prediction becomes. A 24-hour forecast is far more reliable than a 10-day forecast because small measurement errors grow over time.

Air Masses & Fronts

An air mass is a large body of air with uniform temperature and humidity. When two different air masses meet, the boundary between them is called a front. Fronts are the main drivers of short-term weather changes.

Ground Level Cold Air Dense, high pressure Sinks downward Warm Air Less dense, low pressure Rises upward FRONT

The Core Prediction Rule

1. Observe Collect current data 2. Compare Match to patterns 3. Predict Assign probability Example Output Falling pressure + warm humid air = 80% chance of rain in 12 hours

Pressure Tells the Story

Pressure (mb) Time (hours) 1030 1020 1010 1000 990 0 12 24 36 48 Pressure dropping Storm likely approaching Leveled off: storm arrives
Rising Pressure
Fair weather likely: clearing skies, lower humidity.
Falling Pressure
Stormy weather approaching: clouds thicken, precipitation probable.

Cloud Types as Clues

Cirrus
Thin, wispy, high altitude. Often signal a warm front approaching in 24-48 hours.
Cumulus
Puffy, flat-bottomed. Fair weather when small; towering cumulus can mean thunderstorms.
Cumulonimbus
Tall, dark, anvil-shaped. Strong indicator of severe weather: heavy rain, lightning, hail.

Cold Front vs Warm Front

Cold Front Warm Front
Speed Fast-moving Slow-moving
Cloud Type Cumulonimbus, towering Stratus, cirrus layers
Precipitation Heavy, short bursts Steady, light to moderate
Temp After Passing Drops sharply Rises gradually
Pressure Change Falls then rises quickly Falls slowly then stabilizes
Duration Hours 1-2 days

Step-by-Step Forecasting

1
Gather current data. Record temperature, pressure, humidity, wind speed, and wind direction.
2
Observe the sky. Note cloud types, coverage, and any changes over the past few hours.
3
Check trends. Is pressure rising or falling? Is temperature climbing or dropping? Trends matter more than single readings.
4
Identify the front. Determine if a cold, warm, or stationary front is nearby using weather maps.
5
Assign probability. Based on matching patterns, state the likelihood: "There is a high/moderate/low chance of..."

Example 1: Morning Observations

7:00 AM Readings Temp: 18 °C (steady) Pressure: 1008 mb (falling) Humidity: 85% (rising) Wind: South, 20 km/h Clouds: Thickening stratus Prediction Warm front approaching Steady rain probable ~80% chance rain within 6-12 hours

Example 2: Afternoon Shift

2:00 PM Readings Temp: 32 °C (hot) Pressure: 1005 mb (falling) Humidity: 75% (high) Wind: SW, gusting 30 km/h Clouds: Towering cumulus Prediction Thunderstorms likely Heavy rain + lightning ~70% chance severe storms by evening

Example 3: Clear Skies Ahead?

6:00 AM Readings Temp: 12 °C (cool) Pressure: 1024 mb (rising) Humidity: 40% (low) Wind: NW, light 8 km/h Clouds: Few scattered cirrus Prediction Fair weather continues Clear to partly cloudy ~90% chance dry conditions all day

Confidence Decreases Over Time

Accuracy (%) Forecast Range (days) 100 80 60 40 20 0 1 3 5 7 10 HIGH MODERATE LOW

Common Mistakes

✕ Single Data Point
Using only one variable (like temperature) to predict weather. You need multiple variables together.
✕ Ignoring Trends
Looking at a single reading instead of tracking changes over time. A pressure of 1010 mb means little without knowing if it is rising or falling.
✕ Certainty Language
Saying "it will rain" instead of "there is a high probability of rain." Weather predictions are probabilistic, not certain.

Evidence Summary Table

Evidence Suggests Probability
Falling pressure + stratus clouds Rain approaching High (70-90%)
Rising pressure + clear skies Fair weather continues High (85-95%)
Hot, humid + towering cumulus Thunderstorms Moderate (60-75%)
Rapid pressure drop + dark clouds Severe storm imminent Very high (85%+)
Cirrus clouds + steady pressure Weather change in 24-48h Moderate (50-65%)

Question 1 of 5

A barometer shows that air pressure has been steadily falling for the past 6 hours, and thick stratus clouds are moving in. What is the most likely short-term weather prediction?

Question 2 of 5

A weather forecast states: "40% chance of rain tomorrow." What does this mean?

Question 3 of 5

Which combination of evidence best supports a prediction of continued fair weather?

Question 4 of 5

A student says: "The pressure is 1012 mb right now, so it will definitely rain." What is the biggest problem with this prediction?

Question 5 of 5

Why are short-term weather forecasts (1-2 days) more reliable than long-term forecasts (7-10 days)?