Weather

Weather is the current state of the atmosphere.

There are many factors that “cook” up our weather!

Factor #1: The Sun

Solar radiation is the major source of heat for our Earth’s weather.

Lab: What’s the Angle?

Together, the sun angle and day length determine the total amount of solar radiation incident at the Earth.

Factor #2: The Greenhouse Effect

Greenhouse Effect

Factor #3: Earth’s Rotation

If the Earth did not rotate, air would sink south from the cold polar regions and rise north from the warmer tropics.

But the Earth does rotate causing a curvature in the wind paths.

The Coriolis effect explains the direction of movement of air masses.

Factor #4: Air Masses

Air masses are large bodies of air that takes the characteristics of the area over which it forms.

SymbolAir MassCharacteristics cAContinental arcticBitterly cold, dry cPContinental polarCold, dry cTContinental tropicalHot, dry mPMaritime polarCool, moist mTMaritime tropicalWarm, moist Air masses are classified according to their source region.

Each air mass has a different temperature associated with it.

Fronts occur where two large air masses collide at the earth's surface.

A front is the narrow region separating two air masses of different densities.

Fronts are caused by winds moving one air mass away from its birthplace.

In a cold front, cold dense air displaces warm air forcing it up along a steep front.

Clouds, showers and sometimes thunderstorms are associated with cold fronts.

In a warm front, advancing warm air displaces cold air producing a gradual frontal slope.

A warm front is characterized by extensive cloudiness and precipitation.

Stationary fronts occur when neither warm nor cold air advances.

The two air masses reach a stalemate. That is what stationary means - that neither front is moving.

Temperatures remain stagnant and winds are gentle to nil.

These type of conditions can last for days, producing nothing but altocumulus clouds.

Occluded Front is when a cold front overtakes a warm front.

Steady rains fall at an occluded front.

#1 = Cold Front #2 = Warm Front #3 = Occluded Front #4 = Stationary Front

Lab: Air Masses

Lab: Fronts

Factor #5: Water Vapor

The air's capacity for water vapor increases as air temperature increases. Air with a temperature of 30°C can hold more than three times as much water vapor as air at 10°C.

Relative humidity is the percentage of moisture the air holds relative to the amount it could hold at a particular temperature.

Factor #6: Air Pressure

A "high" is an area where the air's pressure is higher than the pressure of the surrounding air. A "low' is where the air pressure is lower.

Air descends in a high pressure system. Air ascends in a low pressure system.

Differences in air pressure causes wind.

A trough is an elongated area of low atmospheric pressure that can occur either at the Earth's surface or at higher altitudes. Cold air plunges south, carving out trough. Ahead of trough rising air causes precipitation.

Measuring Weather Conditions

Station Reporting Symbol

The value highlighted in yellow located in the upper left corner is the temperature in degrees Fahrenheit. The reported temperature is 64 degrees.

Wind Speed Anemometer

Wind Direction Wind Vane

The symbol highlighted in yellow is known as a "Wind Barb". The wind barb indicates the wind direction and wind speed.

Each short barb represents 5 knots, each long barb 10 knots.

A long barb and a short barb is 15 knots, simply by adding the value of each barb together (10 knots + 5 knots = 15 knots). The wind barb indicates winds from the Southeast.

Lab: Wind Speed

Lab: Jersey Winds

Lab: Doppler Effect

Air exerts pressure on a surface. You don't feel the pressure because air is pushing equally on all sides.

Air pressure is measured using a barometer.

Air pushes down on the mercury. The pressure causes the mercury to rise up the vacuum tube. The tube is calibrated in inches or millimeters.

The aneroid barometer does not use a liquid to measure pressure. It is not as accurate as a mercurial barometer.

Manometers indicate the difference between two pressures when one side is open to atmosphere. If a U-tube is filled to the half way point with water and air pressure is exerted on one of the columns, the fluid will be displaced.

The difference in height "h" which is the sum of the readings above and below the half way point, indicates the pressure in inches of water column.

The value highlighted in yellow located in the upper right corner represents the last three digits of the observed pressure reading in millibars (mb).

The black numbers are station reports of sea-level pressure in millibars.

Isobars are normally drawn at 4 mb intervals, with 1000 mb being the base value.

If reported value less than 500: Initial 10 is missing. Place it on left, then divide by 10. For example: 027 becomes mb.

Lab: Isobars

At higher altitudes, air exerts less pressure. Temperature can also affect air pressure since air is a gas that expands when heated and contracts when cooled. The pressures were corrected to show what they would be at sea level.

A red " L " means low pressure (which can mean storminess). Most fronts extend from low-pressure centers. A blue " H " means a center of high pressure (usually calm, sunny weather).

Air descends in high pressure area (A) and rises in low pressure area (B).

This combined with the Coriolis effect results in the formation of rotating low or high pressure systems in the atmosphere.

Winds flow clockwise around a high pressure center in the northern hemisphere, while in the southern hemisphere, winds flow counterclockwise around a high.

Winds flow counterclockwise around a low pressure center in the northern hemisphere, while in the southern hemisphere, winds flow clockwise around a low.

The value highlighted in yellow located in the lower left corner is the dew point temperature in degrees Fahrenheit.

The dew point temperature is the air temperature where the moisture in the air begins to condense or change from a vapor to a liquid.

The dew point temperature is always the coldest of the three temperatures.

In order for a surface to collect dew out of the air, the temperature of that surface must be at or below the dew point temperature.

The reported dew point temperature is 58 degrees.

Humidity is the amount of moisture in the air.

Relative humidity is calculated using a psychrometer sling. It holds the two thermometers and provides a mechanism for you to whip them around to accelerate air exposure and get a more accurate reading.

Relative humidity is determined by calculating the difference between the two thermometers.

Lab: Relative Humidity

The symbol highlighted in yellow indicates the type of weather occurring at the time the observation is taken.

The symbol highlighted indicates fog was reported.

The symbol highlighted in yellow indicates the amount of cloud cover occurring at the time the observation is taken.

Weather Instruments InstrumentWhat it measures Common Units of Measure ThermometerAir temperatureCentigrade (Celsius), Fahrenheit

Weather Instruments InstrumentWhat it measures Common Units of Measure ThermometerAir temperatureCentigrade (Celsius), Fahrenheit BarometerAtmospheric Pressure Isobars, Millibars, Inches of Mercury

Weather Instruments InstrumentWhat it measures Common Units of Measure ThermometerAir temperatureCentigrade (Celsius), Fahrenheit BarometerAtmospheric Pressure Isobars, Millibars, Inches of Mercury PsychrometerRelative HumidityPercentage (%)

Weather Instruments InstrumentWhat it measures Common Units of Measure ThermometerAir temperatureCentigrade (Celsius), Fahrenheit BarometerAtmospheric Pressure Isobars, Millibars, Inches of Mercury PsychrometerRelative HumidityPercentage (%) AnemometerWind SpeedKilometer per hour, Miles per hour

Lab: Making a Weather Map

Controlling The Weather

Drought Prevention

Cloud Seeding

Project STORMFURY

Hail Cannons

A Hail Cannon is a shock wave generator used to disrupt the formation of hailstones in the atmosphere in their growing phase.

The device is repeatedly fired every 4 seconds over the period when the storm is approaching and until it has passed through the area.