Download Air_Masses_and_Fronts

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 temperature
Moisture determined by whether it forms
over oceans or continents
c continental = dry
A=
Arctic
P=
Polar
T=
tropic
m marine = moist
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 MidLatitudes
Lows
(occluded
fronts) Form
CounterClockwise
rotation
OCCLUDED FRONT
Warm 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 weather
After 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
LAKE EFFECT - SNOW
Box 9.2
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)