Download Ch 20 - Weather Patterns and Severe Storms

Ch 20 - Weather
Patterns and
Severe Storms
Air Mass = a large body of air
with the same temperature
and moisture throughout
-Carry the moisture &
temperature from where it
originally formed
EX: Polar Air Mass = frigid
temps.
Named according to their
source area:
Polar = cold temps
Tropical = warm temps
Continental = formed over land (dry)
Maritime = formed over water (moist)
Types of Air Masses that affect
the US
1.
Continental Polar (cP) =
forms over northern
Canada, interior of
Alaska, and Arctic
areas
-
-
Bring cold & dry
weather in winter, cool
& dry weather in
summer
Clear skies, little
precipitation
Also causes lake-effect
snow around great
lakes
2. Maritime Tropical (mT) =
forms over the warm
waters of the Gulf of
Mexico, Caribbean Sea,
or Atlantic Ocean
-
-
-
Bring warm & wet
weather to areas
Cause of high summer
temperatures & high
humidity
Affects Mid-West &
Eastern US
Unstable
3. Maritime Polar (mP) =
form over North
Pacific or North
Atlantic
- Affects weather of
Western US & New
England
- Brings low clouds &
showers, decreased
temperatures
- Nor’eastern = cold
temps & snow
4. Continental Tropical
(cT) = begin in the
southwestern US and
Mexico during summer
- create hot & dry
weather systems
- Rarely move
outside their source
region but can cause
drought-like conditions
in Great Plains AND mild
fall weather in Midwest
(Indian Summer)
Happy St.
Patrick's
Day!
20.2
Fronts
= formed when 2 different air masses meet
- usually bring some form of precipitation
- narrow/small size
- warmer (less dense) air will always rise above
cooler (more dense) air
Types of Fronts:
1. Cold Front = forms
when cold, dense
air moves into a
region occupied
by warmer air
- Warmer air is forced to
quickly rise creating
heavy downpours and
fast winds
- Tall cumulus clouds
indicate approach of
cold front
- fast moving
- bring violent
weather
- After front has
passed,
temperatures
drop
• 2. Warm Front = forms when warm
air move into an area formerly
covered by cooler air
- warm air rises,
cools, condenses to
form clouds, and
frequently creates
precipitation
- Cirrus clouds
indicate approaching
warm front
- as front nears,
cirrostratus &
altostratus clouds
form, later
nimbostratus clouds
bring rain
- slow movement
- produce slight to moderate
precipitation over a large area
- creates gradual increase in
temperature as front passes
- usually brings winds from the
south
3. Stationary Front = occurs when 2
similar air masses
- surface position of front doesn’t move
- produces occasional precipitation
4. Occluded Front = occurs when a cold
front overtakes a warm front
- warmer air is forced upward
creating large clouds
- fronts then merge to create heavy
precipitation
- very slow moving = precipitation for
days
20.3
Thunderstorms
= a storm that
generates
lightning &
thunder, hail,
gusty winds, and
heavy rain
- usually a small
size but sometimes
can stretch for km
along a cold front
- can be
produced from
single
cumulonimbus
- form during
vertical
movement of
warm, unstable
air
- usually form
in tropics (US
gets ~100,000
each year) and
only last for 1-2
hrs
Forms by:
1. Cumulus Stage = strong updrafts
supply moist air to fuel storm, creating tall
clouds
2. Mature Stage = ~1 hr later,
precipitation grows too large for winds to
support = lots of rain, lightning & hail can
also occur during this stage
3. Dissipating Stage = downdrafts
dominate, air temperatures begin to cool,
storm dies
• Within
thunderstorms,
ice crystals and
water droplets
high in the cloud
are torn apart and
later smashed
together =
creates
electricity
• Lightning = electricity
discharged from a
thundercloud
– Can heat the air around
it to 4X the temp of the
sun
– Can go from ground to
cloud, cloud to cloud,
or cloud to ground
The lightning heats the air, causing
it to expand rapidly, creating a large
sound wave = Thunder
– Because speed of light
is much faster than
speed of sound, you will
always see lightning
before you hear
thunder
– To find out how far
away a storm is from
you, count the seconds
between the lightning &
thunder AND divide that
number by 3
= violent windstorms
that take the form of a
rotating column of air
(Vortex) that extends
downward from a
cumulonimbus cloud
- Small tornadoes have 1
vortex, larger tornadoes
have several small
vortexes within a larger
main one
- US reports ~770
tornadoes each year
- max wind speed ever =
480 km/hr
- Tornado season = April
thru June but can occur
any time of year
Tornadoes
• Taken in 1884, this photo is the oldest
known picture of a tornado.
• NOAA Historic Photo Collection
Fujita Scale = scale from 1-5 that
determines a tornadoes intensity
based on wind speed
F0 winds up to 116 km/hr, light damage
F1 winds 116-180 km/hr, moderate damage
(mobile homes overturned)
F2 winds 181-253 km/hr, considerable damage
(roofs torn off, trees snapped)
F3 winds 254-332 km/hr, severe damage (walls
torn
from foundation)
F4 333-419 km/hr, devastating damage (houses
gone, cars carried away)
F5 winds above 419 km/hr, incredible damage
(everything in path is gone)
Tornadoes Cont…
Form by:
1. Vertical cylinder of air develops from an updraft within a
thunderstorm
2. Fast moving winds (Jet Stream?) high in atmosphere
force cylinder to roll/tilt = creates a Funnel Cloud
(Mesocyclone)
3. If pressures within funnel cloud are low enough, air near
ground will be drawn into the cloud = air spirals upward
around the core of the funnel cloud
Problem = there is no “magic” pressure
where a tornado is guaranteed to form at, so
some large storms don’t produce a tornado
while smaller storms sometimes do
Makes prediction of tornadoes almost
impossible and tracking a tornado very
difficult
http://www.youtube.com/watch
?v=bPe0qbXBNlk
• http://www.youtube.com/watch?v=WgP
a3Z-CDCA&feature=related
Hurricanes
= large tropical storms that produce winds of at
least 119 km/hr (tropical storms have winds of 61119 km/hr)
- also known as typhoons, cyclones, and tropical cyclones
- heavy rains, strong winds, extensive flooding
- can generate up 15 meter storm surge (dome of water
about 65 to 80 km wide that moves across the ocean
pushed by winds)
- most deaths result from drowning
- most hurricanes occur between 5-20° N&S latitude
- Pacific is much more likely to produce a typhoon than the
Atlantic
- Winds in Pacific blow typhoons West toward Japan
- Winds in Atlantic blow hurricanes West toward E coast of US
Hurricanes Cont…
- Hurricane season = late summer into late fall
Form by:
1. Begins as a small tropical disturbance of clouds and
thunderstorms (low pressures)
2. Warm water heats air above it, causing the air to rise =
more clouds
3. A central low pressure zone develops and pulls more
warm, moist air inward = spiraling upward winds &
rotation of entire storm (counterclockwise), energy builds
4. Storm begins to gather strength & get bigger over
water, global wind patterns push storm toward land
5. Once storm reaches land, there is no more warm water
to fuel storm, and hurricane eventually dies out
Hurricanes Cont…
- Eye = very center of hurricane, precipitation stops and
winds decrease
- Eye Wall = located just outside eye, large wall of dense
clouds, fastest wind speeds of entire storm, heavy rains
Saffir-Simpson Hurricane Scale
Category 1 = winds 119-153 km/hr, storm surge of 1.2-1.5
meters
Category 2 = winds 154-177 km/hr, storm surge up to 2.4m
Category 3 = 178-209 km/hr winds, storm surge up to 3.6m
Category 4 = winds 210-249 km/hr, storm surge up to 5.4m
Category 5 = winds over 249 km/hr, over 5.4m
Ch 20 Final Assignment
THIS IS WORTH 25 POINTS!
Pg. 583-584
1, 2, 3, 4, 6, 7, 8, 9 = write out both question
& answer
10, 11, 12, 15, 18, 25, 28 = write answer
only in complete sentences
Vocabulary
Cold Front
Eye Wall
Occluded Front
Storm Surge
Eye
Hurricane
Stationary Front
Thunderstorm