air masses and fronts. what is an air mass? air masses are large bodies of air which have similar...
TRANSCRIPT
Air Masses and Fronts
What is an Air Mass?
• Air masses are large bodies of air which have similar temperature and moisture characteristics.
• Air masses form when air stays over a region (called the source region) for several days.
• Air masses that form over water will be moist.
• Air masses that form over land will be dry.
Latitude determines temperatureMoisture determined by whether it forms
over oceans or continents
c continental = dry m marine = moist
A = Arctic
P = Polar
T = tropic
Continental Polar does not move west
Fronts – boundary that separates 2 air masses with different temperatures
Cold Front a. short-lived thunderstorms b. move faster than warm fronts
Warm Front – longer, steady precipitation
Stationary Front
• A stationary front occurs when the air masses on either side of the front are not moving toward each other.
Counter clockwise rotation into Low
Storm moves northeast due to prevailing winds
How Mid-Latitudes
Lows(occluded
fronts) Form
Counter-Clockwise
rotation
OCCLUDED FRONTWarm air mass gets caught between 2 colder air masses and is forced aloft
Occluded Front
Winds spiral clockwise out of the High and counterclockwise into the Low
Fronts are low pressure – lousy weatherAfter the front passes – happy weather
Weather Changes after Fronts Pass
• 2 TOTALLY different air masses so a change in weather
• Temperature changes• Wind direction changes• Wind velocity changes• Dew Point changes• Barometer falls when front approaches and
rises after it passes
BRRR!
WINDS FLOW COUNTERCLOCKWISE IN TO THE LOW PRESSURE SYSTEM – RISING AIR
WINDS FLOW CLOCKWISE OUT OF THE HIGH PRESSURE SYSTEM – SINKING AIR
Hurricanes – counterclockwise low pressure systems (lousy weather)
Weather in a High
• Clockwise Rotation
• Bright, Clear
• Happy Weather
Box 9.2
LAKE EFFECT - SNOW
Thunderstorm Facts
• At any given time there are an estimated 2000 thunderstorms in progress, mostly in tropical and subtropical latitudes. - About 45,000 thunderstorms take place each day
• Annually, The U.S. experiences about 100,000 thunderstorms.
• About 16 million thunderstorms occur annually around the world!
• The lightning from these storms strikes Earth about 100 times each second
Lightning• Within the thunderstorm
clouds, rising and falling air causes turbulence which results in a build up of a static charge. The negative charges concentrate in the base of the cloud.
• This first, invisible stroke is called a stepped leader.
• As soon as the negative and positive parts of the stepped leader connect there is a conductive path from the cloud to the ground and the negative charges rush down it causing the visible stroke.
Tornadoes
• Area of quickly rotating air associated with a thunderstorm
• Some contain winds of over 300 miles per hour
• They can be as small as a hundred yards wide or larger than a mile wide
Development of a Funnel
Damage
Severe Weather Warnings
• Tornado, Severe Thunderstorm, and Flash Flood Warnings
• Severe weather is occurring
• If it is for your area, take shelter right away
• Don’t leave shelter until warning has expired
Severe Thunderstorm Warnings• A thunderstorm with winds of 58 mph or
greater
• Penny sized hail or larger
• Also contain lots of lightning
• Stay inside
• Keep off the phone
• Don’t take a shower or bath
• Stay away from windows
Tornado Warnings
• A tornado or funnel cloud has been detected
• Take shelter RIGHT AWAY!!!
• Get under something sturdy in your basement
• No basement? Go to a room that has no windows like a closet or bathroom
• In mobile homes, leave them and go to a storm shelter if available or lie flat in a ditch
Where we get data
• Weather Stations• Radar• Satellites
Doppler Radar
Next Generation Radar (Nexrad)