Weather

Names of Students in Group:

Background
Most of the weather can be explained if you realize the following:

• Two kinds of broad-scale weather systems dominate the weather. They are Highs and Lows.
• Each kind of weather system has its own common characteristics, including patterns of pressure, temperature, humidity, winds, sky conditions, etc., which are organized around the center of high or low air pressure.
• Weather systems travel across the earth’s surface and carry their traits with them.
• Our weather will change in different sequences depending on the systems affecting your weather and the paths of their centers as they pass by.
• Highs and lows may shift north or south in their travels, but their major motion is from west to east. By knowing what kind of weather system is approaching your area and its probable path, you can make general forecasts of your own.

Highs

The familiar Highs of weather maps are the centers of air masses. They are huge bodies of air, often thousand or more miles across, that form when air resides for days or weeks above warm water surfaces with fairly uniform temperatures. Air resting on cold land cools and is dry. Air above warm water becomes warm and humid. Highs can be pictured as domes of air. They take on circulations of their own as air spirals clockwise (as seen from above) around their centers. Highs typically produce clear skies and fair weather.

Our Weather in a High

While controlled by a High, your weather can be warm or cold, dry or humid, depending on the High’s history. Because the air in Highs sinks and warms, clouds tend not to form and the weather remains fair. (Not all weather in Highs is fair, because there are times and places when the air in them is forced up. Clouds and rain or snow can result.)

As a High approaches you, the air pressure at your location will rise. As it moves away, the pressure will fall. With the passing of a High, wind will gradually change directions. As shown on the WeatherCycler, it will shift in ways depending on whether the center of the system passes by to the north or south of you. Temperatures will change gradually as well. While the system’s center is approaching you, winds will deliver cooler air from the north. Once the center has passed (as the High moves eastward), warmer (and possibly more humid) air will arrive from the south.

Lows

Like oil and water, warm and cold air do not easily mix. Warm and cold air masses in contact remain separated by boundaries called fronts. These boundaries are called warm, cold, and stationary fronts depending on their movements.

Lows form when the boundaries separating air masses begin to pivot around centers of lowering surface pressure. The motion is counter-clockwise around the low-pressure cools, clouds can form, and rain or snow may fall. Weather changes can be dramatic across the fronts.

Our Weather in a Low

The interactions of neighboring air masses cause great variety in the weather. What your weather is during the passing of a Low depends on whether the center of the system passes by to the south or north of you. If it remains to the south as it passes by, you may have an extended period of rain or snow with no sudden weather changes occurring.

If the Low center slips by to the north of you, weather can change from cool and cloudy with rain or snow to warm and fair. Then, showers or thunderstorms may follow. Finally, colder and drier air brings eventual clearing. These conditions are related to the passages of fronts (warm and cold) through your area.

On this online activities, you will use a Weather Cycler to interpret the weather for various specified conditions.

Study Activity I - Weather Maps

Section A Carefully look at the face of The WeatherCycler with the slide pushed all the way in. What you see in the large chart window is a map view of a weather "Low". You can find explanations of common weather map symbols to the lower left of the chart face. " Study this weather map symbols thoroughly before proceeding to the different activities. You will need to know how to interpret the symbols to be able to answer the questions.

 

The "L" marks the middle of a Low. It is called Low because its center is where the air pressure is lowest. Lows are large storm systems that stretch over hundreds of miles or more. It is raining or snowing in the Low wherever the map Select one is is not shaded.

Weather stations are shown on the map as small circles with attached lines suggesting musical notes, or arrows. Look at the station on the map pointed by "A". The wind direction there is given by the arrow shaft. The wind is from the southeast. Since winds are named by the direction from which the wind is blowing, this station has a Select one Southeast Northwest wind.

Look at all the wind directions displayed at stations surrounding the map "L". The general pattern of wind directions in the Low shows winds blow Select one Clockwise Counterclockwise around the center of lowest pressure.

Cloud cover is reported by the way the station circles are filled in. Stations in the shaded areas on the map have reported amounts of cloud cover described as Select one No clouds Completely Overcast

Fronts extend outward from the center of the Low. The blue line with attached "spikes" represents a Select one Warm Cold front.

The WeatherCycler shows that rain or snow usually occurs in a relatively broad band ahead of the Select one Warm Cold front and in a narrow band along the Select one Warm Cold front.

 

Section B Pull The WeatherCycler slide out until the "H” is in the center of the “Surface Weather Map" window. This view represents a major weather system called a “High”.

 

The nearly circular black lines surrounding the “H” connect places that have the same air pressure. They show how air pressure changes in a High with the highest pressure in the center. These lines are called Select one Isotherms Isobars .

Wind directions are generally Select one Clockwise Counterclockwise around the center of the High marked by the “H”.

Skies are generally Select one Clear or Partly cloudy Overcast in a High.

 

Section C Use The WeatheCycler and the following weather map to answer the following:

 

Weather at Location X: The weather at X is controlled by a Select one High Low wind at X is probably from the Select one Southwest Northwest and the sky is clear or partly cloudy.

Weather at Location Y: The weather at Y is controlled by a Low, The wind is probably from the Select one Southeast Northwest . The sky is Select one Clear Overcast , and rain or snow Select one Is Is not likely to be falling.

Study Activity II -Weather in Highs

Section A Turn to your WeatherCycler and pull the slide out until the "H" is centered in the "Surface Weather Map" window. Answer the following:

 

The wind blows Select one Clockwise Counterclockwise around the high-pressure center marked with an "H".

According to the map, skies in a High tend to be Select one Clear Cloudy with the weather generally fair.

Section B With the "H" in the middle of the map window, imagine yourself being on the map at Point B. Now pull the slide out slowly to imitate the typical motion of Highs towards the east. Look at map data and windows below the map to see how your weather changes at Point B.

 

Which sequence better describes the shift in wind direction as the High's center passes by to the north of your Point B location? Select one North, east, southeast South, west, north

According to the window showing air-pressure changes at Point B, which choice describes how the pressure changes as the High passes by? Select one Rising and then falling Falling and then rising

The same chart window shows gradual Select one Cooling Warming at Point B when the air pressure is falling.

Section C Adjust the slide so the “H” is again in the middle of the map window. Now pull the slide out slowly. Imagine yourself on the map at Point A while the High moves towards the east.

 

Which sequence better describes the shift in wind direction as the High's center passes by to the north of your Point A location? Select one Northwest, west, south South, east, northwest

According to the window showing air-pressure changes at Point A, which choice describes how the pressure changes as the High passes by? Select one rising and then falling Falling and then rising

The same chart window shows gradual Select one Warming Cooling at Point A when the air pressure is falling.

 

Section D The High shown on the map at the right is dominating the weather at X and Y. Use The WeatheCycler and the map to answer the following:

 

Weather at X: The wind is probably from the Select one North South ,the sky is Select one Clear Cloudy , and the temperatures are relatively cool.

Weather at Y: The wind is probably from the Select one North South , the sky is Select one Cloudy Mostly clear , and temperatures are relatively cool.

The center of the High is predicted to be to the east of X tomorrow. Tomorrow, X should be Select one Warmer Cooler than today with winds from the Select one North South . The weather at X tomorrow should be similar to the weather at Y Select one Today Tomorrow .

 

Study Activity III -Weather Fronts

Section A Pull out the WeatherCycler slide so that Point B is aimed at a place on the map's (blue) cold front about l/8 inch to the right of the station reporting a 25-knot wind from the northwest.

 

The front is a boundary between warm and cold air. It is called a cold front because it is moving and cold air is replacing warm air at the Earth's surface. The cold front is moving in the direction the blue "spikes" are pointing. The windows below Point B show cold air is Select one Ahead of Behind the front.

Chart windows below Point B shows weather along the cold front is Select one Fair Stormy

Winds ahead of the cold front are from the south-southwest to southwest while winds behind the front are from the Select one Southeast Northwest .

 

Section B Adjust The WeatherCycler slide until Point B is aimed at the first station to the east (right) of the cold front. Now pull the slide out slowly to put the cold front into motion towards the east. Imagine that you remain at Point B while the front passes by.

 

As the cold front approaches you at Point B, the sky Select one Clears Becomes more cloudy .

At the time the front passes Point B, the wind shifts direction until it is coming from the Select one Northwest Northeast and the temperature begins to Select one Rise Fall .

After the cold front passes, the sky Select one Remains cloudy Clears and the temperatures are relatively Select one Cold Warm .

 

Section C Move The WeatheCycler slide until Point B is aimed at the (red) warm front. It should be pointing at a place on the front about ¼ inch to the right of the nearest station west of the front.

 

This boundary is called a warm front because warm air is replacing cold air at the Earth's surface. The warm front is moving in the direction the red semi-circles are pointing. The windows below Point B show the warm air is Select one Ahead of Behind the front.

The windows below Point B show stormy weather is found Select one Ahead of Behind the warm front.

Winds ahead of the warm front are from the southeast while winds behind the front are from the Select one Northeast Southwest .

 

Section D Move The WeatheCycler slide until Point B is aimed at the (red) warm front. It should be pointing at a place on the front about 1/4 inch to the right of the nearest station west of the front.

 

As the warm front approaches you at Point B, the Select one Sky clears Cloudiness increases .

As the warm front passes, your temperature at Point B Select one Rises Falls and the rain or snow Select one Starts Stops .

After the warm front passes, the temperature is relatively Select one Warm Cold and the weather fair.

 

Study Activity IV -Weather in Lows

Section A Push in The WeatherCycler slide all the way. The "L" on the map marks the center of a Low. Answer the following:

 

The wind blows Select one Clockwise Counterclockwise around the center marked by an "L".

Rain or snow is falling in a broad band ahead of the Select one Cold Warm front and in a narrow band along the other front.

The warmest temperatures in the Low are located generally to the Select one South North of the storm system center.

 

Section B With The WeatheCycler slide pushed all the way in. Imagine yourself being on the map at Point A. Now pull the slide out slowly to imitate the usual motion of Lows towards the east. Look at map data and windows above the map to see how your weather changes while you remain at Point A. Answer the following:

 

The center of the Low will pass by the Select one North South of you while you experience Select one One Two period(s) of rain or snow.

Select one No Two fronts will cross your location at Point A as the Low passes.

 

Section C With The WeatheCycler slide pushed in all the way. Imagine yourself being on the map at Point B. Now pull the slide out slowly to imitate the usual motion of Lows towards the east. Look at map data and windows above the map to see how your weather changes while you remain at Point B. Answer the following:

 

The center of the low will pass by the Select one North South of you while you experience Select one One Two period(s) of rain or snow.

Your weather at Point B will first feel the effects of a Select one Warm Cold front. When it passes, the wind will shift until it is coming from the Select one Southwest Northwest .

When the second front arrives at Point B, your temperatures will begin to Select one Rise Fall . At the same time, the wind will shift until it is coming from the Select one Southeast Northwest .

 

Section D Use The WeatheCycler to interpret the map.

 

Weather at Location X: It is relatively cold and wind is from the Select one Northwest Northeast .

Weather at Location Y: The wind is probably from the Select one Southeast Northwest and the sky is overcast.

Since Lows usually move toward the east, Location Select one X Y is the place likely to have greater changes in weather during the next day or so.