1. Unit 6 Chapter 21 Weather Section 1 Air Masses Air masses are caused by differences in air pressure which is caused by unequal heating of the Earth’s surfaces. Equatorial air being warmer and lighter creates a low pressure center. Colder air which is heavier migrates towards the lower presser area. How Air Moves Air moves from high pressure to lower pressure. At high altitudes, air flows from the poles to the equator. This creates the three wind belts which are in turn influenced by the Coriolis Effect. Winds in the Northern Hemisphere turn toward the right. Winds in the Southern Hemisphere turn toward the left.

2. Formation of Air Masses
An air mass is a large body of air in the lower troposphere. It gets its characteristics by forming over specific world areas (source regions). If it forms over a Polar region, it will be cool and dry. In the tropics, it will be warm and moist. When it moves it takes the characteristics with it. The Canadian cool air can travel out to Chicago and cool it. The Gulf of Mexico will effect areas and make them warm and moist.
It can change as it moves into certain areas. When a cold polar mass travels south, but can warm up as it continues to move south.
Types of Air Masses
Air masses are classified according to the source area. The term continental is given to dryer air because it forms over land. The term maritime is given to moist air because it forms over water.
Continental Air Masses
Continental tropical – cT – forms over warm land
Warm and Dry
Continental polar – cP– forms over cold land
Cool and Dry
Continental Arctic – cA – forms over very cold land
Cold and Dry – Winter only
Maritime Air Masses
Maritime tropical – mT – forms over warm tropical seas
Warm and Moist
Maritime polar – mP – forms over cold seas
Cool and Moist
Maritime Artic – mA – forms over very cold seas
Cold and Moist – Extreme North or South only

3. North Atlantic Influences:
Tropical Air Masses
Continental Tropical air masses can form over the deserts of the Southwestern United States. Only forms in the summer.
Maritime Tropical air masses can form over warm waters like the Atlantic Ocean, Caribbean Sea & the Gulf of Mexico. This brings mild, cloudy weather. They may also form over the Pacific Ocean; however, they usually do not reach the coast.
Polar Air Masses
These air masses will form over Northern Canada, Northern Pacific and the Northern Atlantic Oceans. These air masses will influence the weather in North America.
North Atlantic Influences:
In the summer it can produce, cool weather with low clouds & fog.
In the winter it can produce cold, cloudy weather often with snow.
North Pacific Influences:
In the summer it can produce cool foggy weather.
In the winter it can produce cooler weather with rain or snow.

4. Section 2 Fronts Air Fronts
They are the boundary between two different air masses. They contain different conditions in each air mass which is why the weather changes as front pass. They are most common at mid-latitudes where southward-moving polar air masses and northward-moving tropical air masses meet. Fronts usually bring precipitation. They can have steep slopes. They can have a 1 to 50 ratio which means that the temperature raises 1 km vertical to 50 horizontal.
*** AT ALL FRONTS WARM AIR RISES, COOLS FROM EXPANSION, CONDENSATION OCCURS, CLOUDS FORM, PRECIPITATION MAY RESULT***

5. Types of Fronts A front is formed when two air masses collide.
Cold Fronts
Cold Front – Will occur when colder air advances into and area with warmer air. The cold air is denser making it stay toward the ground pushing warm air above it.
Weather Phenomenon
Prior to the Passing of the Front
Contact with the Front
After the Passing of the Front
Temperature
Warm
Cooling suddenly
Cold and getting colder
Atmospheric Pressure
Decreasing steadily
Leveling off then increasing
Increasing steadily
Winds
South to southeast
Variable and gusty
West to northwest
Precipitation
Showers
Heavy rain or snow, hail sometimes
Showers then clearing
Clouds
Cirrus and cirrostratus changing later to cumulus and cumulonimbus
Cumulus and cumulonimbus
Cumulus

6. Warm Fronts
Warm Front – Is when warm air is advancing into an area with colder air. The cold air being dense will sink and the warm air will over ride the cold air.
Weather Phenomenon
Prior to the Passing of the Front
Contact with the Front
After the Passing of the Front
Temperature
Cool
Warming suddenly
Warmer then leveling off
Atmospheric Pressure
Decreasing steadily
Leveling off
Slight rise followed by a decrease
Winds
South to southeast
Variable
South to southwest
Precipitation
Showers, snow, sleet or drizzle
Light drizzle
None
Clouds
Cirrus, cirrostratus, altostratus, nimbostratus, and then stratus
Stratus, sometimes cumulonimbus
Clearing with scattered stratus, sometimes scattered cumulonimbus

7. Stationary and Occluded Fronts
Stationary front
No Frontal Movement. They stall where they are until one air mass eventually gives up.
Occluded Fronts – These will occur when fast moving cold air mass pushes up the entire slow moving warm air mass. This forms large areas of rain because there is a large area of rapid condensation.

8. Weather associated with any low pressure system
A Cyclone is another name for a Low Pressure System.
The lowest pressure is in the center and the winds blow counter -clockwise toward the center.
Remember winds are caused by differences in air pressure; they always blow out from a HIGH PRESSURE and into a LOW PRESSURE area.
Rising air adds more moisture and clouds to all weather fronts.
Typical weather changes associated with a low:
Long periods of clouds (cirrus to cirrostratus, altostratus, nimbostratus and stratus)
Steady rain or snow
Temperature changes as the front passes over
General clearing until next front passes, warms up a bit
More clouds and precipitation as another front passes; scattered showers and possible thunderstorms.
As cold front passes, the temp drops, winds shift and sky clears

9. Anticyclones
An Anticyclone is a High Pressure System. The highest pressure is in the center and the winds blow clockwise out.
Weather associated with any high pressure system
Little to no wind.
Days are hot, nights are cooler
If the system stays for awhile, it can bring droughts.

10. Severe Weather
This is classified by any storm that causes damage to property or life.

11. Thunderstorms
There are approximately 44,000 storms per year. They form as warm air rises very quickly. If the condensation is rapid, you will have quick heavy rain. There will always be thunder and lightening associated with this storm. It may have strong winds, hail, and tornadoes. Most will usually form in afternoon when surface warming causes unstable air.
Local (air-mass) thunderstorms – form as a land area is heated in a warm moist air mass. Causes widely scattered short storms
Frontal Thunderstorms – as a cold front pushes into a warm moist air mass the warm moist air pushes up quickly forming a row of thunderstorms that last up to a few hours.

12. Squall Line
A Squall line is a thunderstorms that occurs in a line ahead of a front. Strong winds precede the line and is caused by the rain cooling the air
Super Cell
Very large single cell thunderstorms with strong updrafts.
Can cause a tornado
Causes the most damage by wind and hail

13. and even ground to cloud (studies made)
Lightning
Lightning is caused by the movement of electrical current. Positive and negative charges create a spark. The spark travels along the narrow path of charged ions and becomes a bolt. Lightening will strike the highest point. It can heat the air to approx. 25,000o C. Flows best through metal, water and wet ground.
Can occur from:
cloud to ground
cloud to cloud
around its own cloud
and even ground to cloud (studies made)

14. Thunder – the temperature of the lightening is hotter than the surface of the sun which causes the air to expand quickly – causing the booming sound. Light travels at 3.0 x 108 m/sec or 186,000 miles/sec Sound travels at 3.0 x 103 m/sec or 11 miles/sec Therefore lightening is always seen before it is heard

15. Emergency Plan for Thunder/Lightening StormsDo
Stay Calm
Go into a building
Unplug appliances that are not surge protected
Stay in your car, all appendages in
Have emergency kit available
Have a plan
Don’t Do
Panic
Go under a tree
Stick you hands out of a car window
Play Golf
Swim in a pool or body of water
Be stupid

16. Hurricanes
A hurricane is an intense tropical low-pressure area with sustained winds of at least 75 miles per hour (120 km) or greater. The storm contains strong winds and heavy rains, which cause damages to property. Winds spiral toward the center or the eye. The eye of the storm has almost no wind and no rain at all. They are most common in the late summer and early fall in the NH.
To Form
1. Supply of warm, moist air for a long period of time
2. Water condenses, releasing large amounts of heat
3. starts to rotate (coriolis effect)
4. Does not form at the equator (usually between 5oand
20o Latitude)

17. Hurricane Ivan 2004

18. Super Storm Sandy 2012

19. Typhoon hitting Taiwan 2005
In the SH they are called typhoons or tropical cyclones. Atlantic hurricanes start as lows as far away as West Africa; Pacific hurricanes form to the west of Mexico and move westward; occasionally they move north to California or west to Hawaii

20. Storm Surge –
When a hurricane piles up water along the shore and then blows it inland; very dangerous during high tide. It can raise sea level several meter high.
On the East Coast meteorologists announce the percent chance that the eye will pass within 105km. 1
119 – 153 km
Minimal
Moves trees, unanchored mobile home, some coastal flooding 2
154 – 177 km
Moderate
Minor building damage, some trees blown down 3
178 – 209 km
Extensive
Some structural damage to small buildings, mobile homes destroyed 4
210 – 250 km
Extreme
Some roofs destroyed, evacuation as far a 10 km inland 5
> 250 km
Catastrophic
Buildings destroyed, evacuation as far as 16 km in land

21. Emergency Plan for Hurricanes
Evacuate the area if you are told to do so
Find a sturdy room to stay in away from windows
Keep battery powered phone/radios handy
Get out of a mobile home, find better shelter
Store fresh water and canned goods incase there is no power
Don’t panic make sure you know the drill

22. Tornadoes
A tornado is a funnel shaped clouds that extends down from a thunder cloud with winds from 100 – 300 m/h. There are more in the US than anywhere else in the world; (Great Plains, South Dakota to Texas – Tornado Alley) however, Europe does get tornadoes. Cool air from the Rocky Mts meets warm wet air from the Gulf of Mexico. Only about 1/3rd become tornadoes. You may get one without a mesocyclone. They are driven by upper level winds

23. To form a Tornado
You need a rotating updraft within a severe thunderstorm (called a mesocyclone)
The rotating cloud can become visible and form a wall cloud.
10 – 20 minutes later, there may be a descending tornado.

24. Shapes
Some are a vortex, or funnel-shaped cloud
Some are rope shaped
They are created when air in the center (which is low pressure) is sucked into the funnel expanding and cooling the air. The water vapor in the air condenses and forms a cloud.

25. The Tetsuya Fujita Scale
65 – 118 km
Minor damage – break some windows F1 km
Downs trees, shifts mobile homes F2
182 – 253 km
Rips roofs off, destroys mobile homes F3
254 – 332 km
Lifts cars, partially destroys buildings F4
333 – 419 km
Levels sturdy buildings, tosses cars F5
420 – 513 km
Lifts and transports sturdy buildings

26. Blizzard
A blizzard is a snowstorm with high winds and real cold temps. There doesn’t have to be a massive amount of snow, but it does have to have high winds.
winds exceed 56 km
temps are approx -7o C or lower
Snow falling or blowing must reduce visibility

27. Section 3 Weather Instruments
Weather Forecasts-
Information is gathered from surface equipment, commercial planes, satellites, weather balloons, etc. All data from around the world, is transmitted (at Midnight and Noon) to a central bank of computers at the National Meteorological Center in Camp Springs, MD, where it is made into weather models based on past weather patterns.
Local and Commercial weather services takes that information and makes predictions based on the areas past and local weather conditions.

28. Measuring Lower Atmospheric Conditions
During the day the atmospheric pressure can change drastically in a short period. Meteorologists use the magnitude and speed of the changes to predict future events.

29. Air Temperature
Thermometers are used to measure the temperature of the air. They either have alcohol or mercury in the tubes to indicate changes.
Electrical thermometer use a current to measure the change
A thermistor or thermal register is the most accurate and quickest indicator for temperature changes. They are used when you need to monitor rapid temperature changes.

30. Air Pressure
A Barometer is used to measure the changes in air pressure.
Reasons for movement of air
Hot air rises therefore it weighs less (molecules move farther apart)
Cool air sinks therefore it weighs more (molecules move closer together)
Relative humidity changes (more water- less weight).
Air is 78%- Nitrogen Weighs 28
21%- Oxygen Weighs 32
1%- all other gases with some water
Water weighs 18
When the air is more humid there is more water in the air, which replaces the heavier nitrogen and oxygen. This makes the air weigh less and lowers the air pressure.
High (H) pressure- generally cool and dry (fair)
Pressure- anything above mb
Clockwise rotation
Low (L) Pressure Anything below mb
Pressure generally warm and humid (precip)
Counter-clockwise rotation

31. Wind Speed Anemometer - Measures wind speed 10 meters above ground.
- Can be hand held or ones mounted on poles.
- Used by all airports
- Measures both speed and direction (vector quantity)
*** A wind is named for the direction from which it comes****

32. Other Ways to check wind speed:
White Caps occur in winds approx 20-30km/hr
Umbrellas break with winds approx 40km/hr
Trees uprooted with winds approx 90km/hr

33. Wind Direction Wind Vanes-
A wind vane is an instrument that has an arrowhead on one end and a broadtail on the other. The tail resists the wind (tail opposite direction of wind). Always point the direction that the WIND CAME FROM.

34. Measuring Upper Atmospheric Conditions
Surface Observation
Using weather stations to assist especially in areas or times that other equipment could not be used. Most weather stations are at airports. People are also used to phone in any unusual conditions which increase the chances of citing these events.

35. Radiosonde
This is an instrument package that is carried into the atmosphere on a balloon. It will measure Relative Humidity, Air Pressure and Temperature. The balloon is tracked to record speed and altitude and intensity of precipitation also.

36. Radar Regular Radar – Doppler radar (Doppler Effect) –
To use the radar, meteorologists emit pulses of microwaves and wait for them to bounce back when they hit precip. The time it takes for the wave to return is how far away the storm is. Not always very accurate since it does not detect the true shape of some storms.
Doppler radar (Doppler Effect) –
This shows winds moving toward or away from the instrument. Radar waves reflected by particles moving toward the radar are shorter than waves moving away. These are transferred to a color screen, which uses colors to determine strength and speeds. For tornadoes they can get about 20 minute warning.

37. Weather Satellites – Satellites are able to take readings from orbit that fills in the missing information. It can also take pictures form space showing cloud movement. This is done every 30 minutes.
Visible Images They are black and white pictures of the earth. White is sunlight reflected (brighter means thick clouds) gray is land and black is water. These are used to estimate severity and stages of hurricanes. The disadvantage of this is that it is not available at night
Infrared
This uses temperature so it can be used day or night. Bright areas are cold temps, dark areas are warmer. Can be used to determine how tall clouds are. Can estimate wind speed, direction and altitude of wind, and water vapor.

38. Computer Models
Computers collect atmospheric pressure, humidity, temperature, wind speed and direction and precipitation. They use all the conditions in an area to predict current and future weather based on the current conditions and past weather movements.

39. Section 4 Forecasting the Weather
This was not easy to do until the invention of the telegraph in This allowed Meteorologists to share the information and help piece together a forecast.
Local weather stations send information hourly to the National Weather Station. Westhampton Beach is a NWS and so it Upton (Brookhaven National Lab)
Map of all these stations are made every 3 hours by the National Center for Environmental Protection (NCEP)
Putting the maps together makes it a time lapses picture

40. Global Weather Monitoring
Weather stations report conditions several times per hour. They monitor barometric pressure and how it has changed, the speed and direction of the wind, precipitation, temperature and humidity. They also record the amount and height of cloud cover along with the general weather condition. This information is sent and gathered at a collection center that disperses the information world wide.
The World Meteorological Organization (WMO) is an organization that helps train and promotes people to watch the weather and report the conditions.

41. Weather Maps
Information is collected and transferred on to maps so Meteorologists can use the information to understand current weather conditions in order to make some form of forecast.

42. Weather Symbols
A Station Model is used to plot the information on a weather map. It is a cluster of meteorological symbols that represent weather conditions.

43. Things to remember:
Below 500 add a 10 to the front and decimal point between the last two numbers.
Above 500 add a 9 to the front of the number and a decimal point between the last two numbers.
The barometric trend is in code too. There should be a decimal between the two numbers. This represents what has happened to the pressure over a period of 3 hours.
Wind is named for the direction is comes from
Temperature and dew point temeprature is listed in F not C

44. Plotting Temperature and Pressure
Isobars are lines that connect areas of equal pressure. They can show High and Low Pressure areas on a weather map.
Isotherms are lines of equal temperature. Some times they are also represented by color too.

45. Plotting Temperature and Pressure
Some weather maps will color code the precipitation according to the type. Light green usually represents a light rain, while gray to white will represent snow. See weather map above.

46. Weather Forecasts Weather Data
Most meteorologists know they can not predict the weather. They take all the information and put it together. They also take into consideration the history, topography, geography and urbanization of an area. The most accurate forecasts are the short range ones, like 2 – 3 days.
Weather Data
Meteorologists use various radars and computers to enhance the information. The different models represented by the computers allow them to compare what the other areas see. Since different people and equipment collect and put together the information, there may be slight differences to the data; this is why meteorologists use different sources to help make the forecasts
Temperature, wind direction, wind speed, cloudiness and precipitation are the variables that are forecasted with the most accuracy.

47. Severe Weather Watches and Warnings
Types of Forecasts
Daily – the most accurate when they predict for approximately a 48 period.
Extended- usually some accuracy, but predicts for a 3 – 5 day.
Medium Range – not very accurate for a 3 -7 day period
Long Range – the least accurate, but predicts for a day period
Severe Weather Watches and Warnings
Meteorologists can track a weather condition from the beginning to the end which will help decide what action to take.
Watch-
24 – 36 hours away
Warning
24 or less hours away

48. Controlling the Weather
Some scientists try to cloud seed but they are not as successful as they want to be. In Russia some scientists have had success seeding rain clouds so that they did not produce hail.
Hurricane Control
Project Stormfury was established in order to try to stop or slow down hurricanes. This project which took place from seeded 4 hurricanes with mixed results.
Lightning Control
Scientists try to seed the clouds to disperse the lightning, but they have very little luck. Meteorologists have trouble predicting when and where lightning will strike so this often fails. They use artificially made lightning to help with the control of this.