WEATHER - AIR MASSES

AIR MASSES & FRONTS - VIDEO

Large body of air with similar temperature and moisture characteristics in any horizontal direction

• cover many 1000's of square kilometers
• Part of weather forecasting is determining air mass characteristics, how they may be modified, and their movement

AIR MASSES

AIR MASS SOURCE REGIONS - DEFINED

• Air masses originate in source regions
• source regions:
  • flat, uniform composition
  • light winds
• So, where are the good source regions?  
• snow covered Artic plains, tropic-subtropic oceans, forests, mountains, large bodies of water
• Air masses tend to clash and interact in the middle latitudes.

Air Mass Characteristics

There are two main characteristics that define air masses - 

• temperature and moisture content. 
• Generally, the temperature and moisture content of air masses are abbreviated as two letters. 
• The first letter is a lower case letter and is used to symbolize the overall moisture in the air.
• The second letter used to symbolize a type of air mass is capitalized. The capital letter symbolizes the temperature or thermal properties of the air.

AIR MASS CLASSIFICATION - VIDEO

4 general air mass classifications categorized according to the source regions. Source regions should be:

1. uniform surface composition - flat
2. light surface winds

1. polar latitudes P - typically located poleward of 60 degrees north and south
2. tropical latitudes T - typically located within about 25 degrees of the equator
3. continental c - located over large land masses--dry
4. marine m - located over the oceans----moist

We can then make combinations of the above to describe various types of air masses.

cP	continental polar	cold, dry, stable
cT	continental tropical	hot, dry, stable air aloft--unstable surface air
mP	maritime polar	cool, moist, and unstable
mT	maritime tropical	warm, moist, usually unstable

• four general categories according to source region (see table)
• extremely cold cP air is sometimes denoted at cA
• extremely hot, humid mT air is sometime denoted by mE

Arctic air is often symbolized with an A. This type of air mass is characterized by extremely cold temperatures. Equatorial air is symbolized with an E. The air is hot because it originates in the equatorial regions.

It is important to remember that the classification system for an air mass is based on source region and not the destination of the air mass. As the air mass moves over Earth, the characteristics can slowly change and the air mass itself will eventually change.

Air Masses on the move:

• if an air mass is colder than the surface over which it is moving, "k" is added
• if an air mass is warmer than the surface over which it is moving, "w" is added

Example - a cP air mass moving over the great lakes in December becomes cPk

Source Region	Polar	Tropical
Land - continental (c)	cP (cold, dry, stable)	cT (hot, dry, stable air aloft; unstable surface air
Water - maritime (m)	mP (cool, moist, unstable)	mT (warm, moist; usually unstable)

Five Air Masses affect the U.S. during the course of a typical year:

• continental
• polar
• continental arctic
• continental tropical
• mmaritime polar
• maritime tropical

Continental air masses are characterized by dry air near the surface while maritime air masses are moist.
Polar air masses are characterized by cold air near the surface while tropical air masses are warm or hot. Arctic air masses are extremely cold.

Air masses in the U.S. include:
cP -- wintertime bitter cold can extent to Southern US and even Florida causing crop damage. Require long, clear nights, which means strong radiational cooling of air near the surface. A stable air mass. Little moisture added so air is dry
mP -- Winter cP air moves over a region such as the NE Pacific, picking up some warmth and moisture from the warmer ocean. In the case of the Pacific NW mountains force the air to rise (orographic lifting) causing rain.
mT -- wintertime source for the SW US is the subtropical East Pacific Ocean. mT air that influences weather east of the Rocky Mountains comes from the Gulf of Mexico, but only influences winter weather in the SE states. Occasionally, slow moving weather systems in SW flow aloft can draw up moisture at mid and low levels producing precipitation.
cT -- Continental tropical air usually only influences the US in summertime as warm, dry air is pumped up off of the Mexican Plateau. It is usually fairly stable and dry, and if it becomes stagnant over the midwest, results in a drought. Deaths associated with the 1995 heat wave in the midwest were the result of cT and mT air which stagnated over the central and eastern part of the US this last summer.
Air masses can control the weather for a relatively long time period: from a period of days, to months. Most weather occurs along the periphery of these air masses at boundaries called fronts.

 Continental polar (cP) or continental arctic (cA) air masses are cold, dry, and stable.

• These air masses originate over northern Canada and Alaska as a result of radiational cooling. They move southward, east of Rockies into the Plains, then eastward. Continental polar or continental arctic air masses are marked by surface high pressure, cold temperatures, and low dew points.

Maritime polar (mP) air masses are cool, moist, and unstable.

• Some maritime polar air masses originate as continental polar air masses over Asia and move westward over the Pacific, collecting warmth and moisture from the ocean. Some mP air masses originate from the North Atlantic and move southwestward toward the Northeast States. The latter air mass generally is colder and drier than the mP off of the Pacific.

Maritime tropical (mT) air masses are warm, moist, and usually unstable.

• Some maritime tropical air masses originate in the subtropical Pacific Ocean, where it is warm and air must travel a long distance over water. These rarely extend north or east of southern California. Some maritime tropical air masses originate over the Gulf of Mexico and Caribbean Sea. They can be associated with fog and low clouds as they moves northward. In the spring and summer, this air mass accounts for the thunderstorms in the Great Plains and elsewhere.

Continental tropical (cT) air masses are hot, dry, unstable at low levels and generally stable aloft (upper-level ridge)

• Continental tropical air masses originate in northern Mexico. They are characterized by clear skies and negligible rainfall. If one moves into the Great Plains and stagnates, a severe drought can result.

Air masses can be modified significantly as they pass over regions with different characteristics. When air masses are modified, they are renamed according to their new characteristics.
Topography can play a crucial role in the modification of air masses. For example, the Rocky Mountains cause flow from the west to be lifted over the mountains. The originally mP air loses its moisture as it precipitates, leaving dry air to move eastward. Hence, mP air becomes cP air after it is forced over the Rockies.

Most large-scale weather events occur at the boundary of two or more air masses.

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AIR MASSES - SOURCE REGIONS

Source region is the location from which an air mass originates. 
Examples of source regions include the icy continental portions of Canada in the winter. As a giant parcel of air moves over this source region, the air will acquire the characteristics of the underlying surface. In this case, the air will be dry (continental) and mild to cold (polar).

The source region in weather usually refers to the location where the different types of air masses formed. 
In general, a source region covers several million square miles. The conditions on the surface of Earth are nearly homogeneous. As an example, the ocean is a common source region for the formation of air masses. Air will remain over the ocean for a period of time sufficient enough to alter the properties of that air parcel.
As an air mass stays over a region, it will acquire the properties of that land or ocean region. For instance, in the example above, the air over the ocean would become moist provided it remain in the same general location for an extended period. Uniformity within the air mass is reached in anywhere from several days to several weeks.  

Air masses can control the weather for a relatively long time period: from a period of days, to months. Most weather occurs along the periphery of these air masses at boundaries called fronts. FRONTS - click Fronts are the boundaries between two air masses. Fronts are classified as to which type of air mass (cold or warm) is replacing the other.  For example, a cold front demarcates the leading edge of a cold air mass displacing a warmer air mass. A warm front is the leading edge of a warmer air mass replacing a colder air mass. If the front is essentially not moving (i.e. the air masses are not moving) it is called a stationary front. Fronts don't just exist at the surface of the earth, they have a vertical structure or slope as well. Warm fronts typically have a gentle slope so the air rising along the frontal surface is gradual. This usually favors the development of widespread layered or stratiform cloudiness and precipitation along and to the north of the front. The slope of cold fronts are more steep and air is forced upward more abruptly. This usually leads to a narrow band of showers and thunderstorms along or just ahead of the front, especially if the rising air is unstable. Cold fronts typically move faster than warm fronts, so in time they "catch up" to warm fronts. As the two fronts merge, an occluded front forms.  In the occluded front, the cold air undercuts the cooler air mass associated with the warm front, further lifting the already rising warm air. Fronts are usually detectable at the surface in a number of ways. Winds usually "converge" or come together at the fronts. Also, temperature differences can be quite noticeable from one side of the front to another. Finally, the pressure on either side of a front can vary significantly. Here is an example of a location that experiences typical warm frontal passage followed by a cold frontal passage: Clouds lower and thicken as the warm front approaches with several hours of light to moderate rain. Temperatures are in the 50s with winds from the east. As the warm front passes, the rain ends, skies become partly cloudy and temperatures warm into the mid 70s. Winds become gusty from the south. A few hours later, a line of thunderstorms sweeps across the area just ahead of the cold front. After the rain ends and the front passes, winds shift to the northwest and temperatures fall into the 40s and skies clear. Cold Front the front edge of a moving mass of cold air that pushes beneath a warmer air mass like a wedge. Warm Front the front edge of advancing warm air mass that replaces cooler air with warmer air. Occluded Front a front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass off the ground and over another air mass.  AIR MASS - QUIZ    FRONTS - QUIZ place your scores on notebook paper

Which is heavier warm or cold air?

WEATHER - MAPS FORCASTING & ACTIVITY

Weather FORECAST

Weather symbols are just as important as the other symbols and signs we see in our day-to-day lives. Weather maps that contain these symbols provide valuable information that lets us know what clothes to wear, when we should seek shelter, or when we should evacuate our homes and move to a safer place. Sometimes there are map keys on the weather maps to tell us what the symbols mean, such as the image shown here. In the real world, however, most weather maps do not have these keys.  You will learn more details & understanding of the symbols & types of weather as we work through the weather unit.  You must keep up on notes!

WEATHER PROJECT PART I

Starting on – Monday, March 3, thru Friday, April 4, you will create a FORECAST LOG.

·         You will study the Moberly area weather map:

©       Date/Time

©       Record temperatures (High/Low for the day in both *F & * C);

©       Temperature (at time of observing the map - *F & *C);

©       Precipitation;

©       Specifics for that day (wind gusting, warnings &/or watches, etc…)

©       Explanation (explain any weather) 

·         You are only required to have weather data recorded in your log each week - Monday thru Friday

·         You can come access weather maps @ home, before or after school using a lap top or use the public library for computer access.  Please discuss with your parents your responsibility for this project.

·         Record these observations in your science notebook forecast log page (see headings below);

©       On notebook paper make a chart with the following headings:  (you will want to turn your paper landscape)

©       DATE/TIME;

©       TEMPERATURE - TIME YOU READ THE WEATHER- F* & C*; TEMPERATURES (HIGH & LOW);

©       PRECIPITATION;

©       SPECIFICS - [WIND, WARNINGS, ETC];

©       EXPLANATION OF WEATHER

·         FORECAST LOG must be neat & easy to read; I will not score if I cannot read!!!

·         Use the weather sites provided to gather weather data 

·         Moberly Weather - http://goo.gl/ZkLJfP

DATE/TIME	TEMPERATURE	TEMP. HIGH/LOW	PRECIPITATION	SPECIFICS	EXPLANATIONS
3/3/2014

WEATHER PROJECT - PART II 

·         Choose a day from March 11 - April 4 to make a weather map 

·         Please let me know what day you choose for your weather map & forecast video.

·         You will receive a weather map for the entire 48 states.  You will add the weather for that day; using symbols; legend, colored pencils.  

·         Use your notes, class discussions, weather symbols handout to help you complete the weather map, as well as your forecast

·         Use the weather sites provided to assist you gathering your data

VIDEO WEATHER FORECAST –

·         You will need to write a script for the weather report.  Discuss any large storms or weather forming in the area.  You will write the report just as you would say it on the video. 

·         Practice presenting your weather report. The report will be NO longer than 3 minutes. 

You will get one take at reporting, so practice is very important.

·         You will use correct weather terminology to describe your forecast.  If the weather has a distinct weather issue you will need to explain (storms - high &/or low pressure, excess air pollution).

·         You will the forecast with National & Moberly weather data

·         READ:  weather forecasting tips to help you understand terms

·         Take your time working through this blog post; spend the time necessary to be acquainted with the different sites listed below.

·         Your SCORE is dependent upon a thorough, detailed completion of the report & presentation of the assignment as well as neatness of the forecast map; 

·         You will address the following in both forecast National & Moberly:

·               date/time of your forecast

·               specific just for Moberly weather data:

·            temperature (current, high/low)

·            humidity

·            wind speed

·            barometer

·            dew point

·            visibility

§            air pollution

·            description of the weather

·            the appropriate weather terms

§   explain the weather terms

·               fun sign off for your forecast!

 TYPES OF WEATHER MAPS - REVIEW

WEATHER MAP - PRACTICE (click Weather Flash)

  weather map - practice activity        

               WEATHER MAP - PRACTICE

#1 - DAILY WEATHER REPORT (click)

#2 - WEATHER MAP WITH SYMBOLS

#3 - DAILY WEATHER

#4 - RADAR MAP

#5 - AIR POLLUTION 

#6 WEATHER MAP

#7 - WEATHER GLOSSARY

TYPES OF WEATHER MAPS

WEATHER FORECASTING TIPS

How do meteorologists forecast the weather?
Weather forecasting is a prediction of what the weather will be like in an hour, tomorrow, or next week. Weather forecasting involves a combination of computer models, observations, and a knowledge of trends and patterns. By using these methods, reasonable accurate forecasts can be made up to seven days in advance. 



What are weather station symbols?
Weather symbols are used on my weather maps as shorthand for the conditions at weather observing stations.

Click Here to see a complete list of all the weather station symbols.
Click Here for an easy print out of the different weather station symbols.

What is a High Pressure System?
A high pressure system is a whirling mass of cool, dry air that generally brings fair weather and light winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere. These bring sunny skies. A high pressure system is represented as a big, blue H.
H

What is a Low Pressure System?
A low pressure system is a whirling mass of warm, moist air that generally brings stormy weather with strong winds. When viewed from above, winds spiral into a low-pressure center in a counterclockwise rotation in the Northern Hemisphere. A low pressure system is represented as a big, red L. 
L

What is a dew point?
The dew point is the temperature at which water starts to condense out of a particular air mass. The dew point temperature changes only when the moisture content of the air changes. The higher the dew point, the greater the moisture content is in the air.

What is humidity?
Humidity is the amount of water vapor in the air.

What is relative humidity?
Relative humidity is the ratio of water vapor contained in the air compared to the maximum amount of moisture that the air can hold at that specific temperature and pressure. Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling ­us off. 

What is an air mass?
An air mass is an extremely large body of air whose properties of temperature and moisture content (humidity), at any given altitude, are fairly similar in any horizontal direction. Air masses can cover large (hundreds of miles) areas. Air masses can control the weather for a relatively long time period: from a period of days, to months. Most weather occurs along the periphery of these air masses at boundaries called fronts. There are 4 general air mass classifications categorized according to the source region: polar, tropical, continental and marine. 

1.) Polar latitudes (P) - located poleward of 60 degrees north and south

2.) Tropical latitudes (T) - located within about 25 degrees of the equator

3.) Continental (c) - located over large land masses, dry

4.) Marine (m) - located over the oceans

We can then make combinations of the above to describe various types of air masses. 

cP continental polar cold, dry, stable

cT continental tropical hot, dry, stable air aloft, unstable surface air

mP maritime polar cool, moist, and unstable

mT maritime tropical warm, moist, usually unstable

What type of air masses affect the United States?
There are many types of air masses that can affect the U.S., since it is such a large country. Below are a few examples: 

cP - wintertime bitter cold can extent to Southern U.S. and even Florida causing crop damage. Require long, clear nights, which means strong radiational cooling of air near the surface. A stable air mass. Little moisture added so air is dry

mP - Winter cP air moves over a region such as the NE Pacific, picking up some warmth and moisture from the warmer ocean. In the case of the Pacific NW mountains force the air to rise (orographic lifting) causing rain.

mT - wintertime source for the SW U.S. is the subtropical East Pacific Ocean. mT air that influences weather east of the Rocky Mountains comes from the Gulf of Mexico, but only influences winter weather in the SE states. Occasionally, slow moving weather systems in SW flow aloft can draw up moisture at mid and low levels producing precipitation.

cT - Continental tropical air usually only influences the U.S. in summertime as warm, dry air is pumped up off of the Mexican Plateau. It is usually fairly stable and dry, and if it becomes stagnant over the Midwest, results in a drought. Deaths associated with the 1995 heat wave in the Midwest were the result of cT and mT air which stagnated over the central and eastern part of the U.S.

What is a front?
A front is a boundary between two different air masses, resulting in stormy weather. A front usually is a line of separation between warm and cold air masses. 


How do you identify a front on a surface weather map or by your own weather observations?
Look for: Sharp temperature changes over a relatively short distance, change in moisture content, rapid shifts in wind direction, pressure changes, clouds and precipitation patterns.

What is a cold front?
A cold front is a boundary between two air masses, one cold and the other warm, moving so that the colder air replaces the warmer air. A cold front is represented as a blue line with the teeth pointing toward the direction on movement. 



What is a warm front?
A warm front is a boundary between two air masses, one cool and the other warm, moving so that the warmer air replaces the cooler air. A warm front is represented as a red line with half circles pointing toward the direction on movement.



What is a stationary front?
A stationary front is a boundary between two air masses that more or less doesn’t move, but some stationary fronts can wobble back and forth for several hundred miles a day. A stationary front is represented as an alternating warm and cold front symbol. 



What is a occluded front?
An occluded front is a combination of two fronts that form when a cold front catches up and overtakes a warm front. An occluded front is represented as a purple line with teeth and half circles. 


What is a trough?
A trough on a weather map is an elongated area of relatively low pressure. Troughs bring cloudy and rainy weather. A trough is represented by a hash mark line. 



What is a weather satellite?
A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while moving at the speed of the Earth's rotation. These meteorological satellites see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., are other types of environmental information collected using weather satellites.


What is radar? 
Radar is an electronic instrument, which determines the direction and distance of objects that reflect radio energy back to the radar site. It stands for Radio Detection and Ranging. This is what meteorologists use to see rain or snow. 


What is Doppler Radar?
Doppler Radar detects precipitation intensity, wind direction and speed, and provides estimates of hail size and rainfall amounts. Doppler Radar gives forecasters the capability of providing early detection of severe thunderstorms that may bring strong damaging winds, large hail, heavy rain, and possibly tornadoes. Combined with satellites, radar gives forecasters the ultimate tools to provide accurate forecasts and advanced severe weather warnings. 

How does Doppler Radar work? 
Doppler Radar gets its name from the Doppler Effect. Have you ever listened to a train whistle as it was coming toward you? You probably noticed that the pitch of the whistle changed as the train passed you and moved away. This change in the frequency of sound is called the Doppler Effect. Doppler Radar measures the changes in the frequency of the signal it receives to determine the wind. 


What is NEXRAD Radar?
The National Weather Service has installed a new type of Doppler Radar called NEXRAD Radar. NEXRAD stands for Next Generation Radar. This radar produces many different views of storms and rain that allows meteorologists to determine if a storm could be severe. 

GOOD LUCK!