Download Where The Fronts Are

Air Masses & Fronts
Ms. Sauer
3/8/13
• Aim: What is an air mass?
• Do Now: How many Joules of heat energy is
required to raise 10 grams of dry air from 32oF
to 48oF?
• Motivation: Learning about weather that
affects are lives everyday.
Air Masses
• A huge body of air in the troposphere, can
be up to 2000 KM in diameter.
• These air masses have similar pressure,
moisture, wind, and temperature
characteristics throughout.
On The Map
• Air masses are labeled with two letters
•
•
•
•
•
indicating the moisture and temperature
characteristics of their source region.
c- Continental
m- Maritime
P- Polar
T- Tropical
Ex. cT= Continental Tropical Air Mass
Source Regions
Source region is the area where air masses come
from.
Air-Masses that develop over the water
(maritime) are moist
Air-Masses that develop over the land
(continental) are dry
Air-Masses that develop in the higher
latitudes (Polar) tend to be cool
Air-Masses that develop in the lower latitudes
(Tropical) tend to be warm
On The Map
Pacific
Ocean
U.S.A.
Atlantic
Ocean
Common air masses of North America
What happens when two air masses
come together?
• A Front Develops
• The line between two different air masses is
called a front
• The front is where all the action or weather
of interest is taking place.
3/11/13
• Aim: How do fronts form?
• Do Now:
1. Which abbreviation indicates a warm air mass that
contains large amounts of water vapor? (cP, cT, mT,
or mP)
2. An air mass originating over north central Canada
would most likely be? (warm & dry, warm & moist,
cold & dry, or cold & moist)
• Motivation: Hands on demonstration.
Low Pressure Center
• Move INWARD &
COUNTERCLOCKWISE
• Converging Winds
High Pressure Center
• Move OUTWARD & CLOCKWISE
• Diverging Winds
What is a front?
• A boundary between two air masses
• At the frontal interface air is unstable
(rising)
• This instability produces clouds, strong
winds, precipitation and other weather
changes.
• Air masses move at different speeds the
leading edge of the faster moving air mass
names the front
Types of Fronts
• Cold Front (the bully)
• COLD AIR is DENSER so is pushes out
warmer air
• Cold fronts MOVE FASTER than warm
fronts
• Cumulonimbus Clouds, a short period of
precipitation, winds move from the North
Cold Front
Cold Front- the air behind the front is cool & dry
Cold fronts have STEEP SLOPES
At the cold front convection is extreme and cumulonimbus clouds form
Precipitation AT THE FRONT
Cumulonimbus clouds produce LIGHTNING, THUNDER, & VIOLENT
WINDS
Cool air moves into warm air, density
differences push warm air upwards
• Cold Front
Types of Fronts
Warm Front
• When warm (wimpy) air meets and rises
over cold air on the ground
• Far ahead of where the front meets the
ground long periods of rain are present until
the Front passes.
• Warm air mass weather will dominate
behind the front
Warm Front
A warm front has a GENTLE SLOPE
Precipitation AHEAD OF THE FRONT
A warm front can extend for hundreds of miles
The first sign of an approaching warm front is the cirrus clouds
Warm Front
Where The Fronts At
Yo!
• A front is the leading edge of an
air mass.
• If it is the front of a cooler air
mass, it will be a COLD FRONT.
• If it is the front of a warmer air
mass, it will be a WARM FRONT.
How to tell where a front
belongs on a map.
• A front will be located where
the temperature changes
rapidly in a short distance.
• Isotherms will be close
together.
30°F
35°F
30°F
40°F
Warmer air
45°F
25°F
Cooler Air
35°F
40°F
50°F
50°F
45°F
Now that we know WHERE
the fronts are, how do we
know what KIND they are?
• It depends on which direction the line
you just drew is moving…
This
line
Now that we know WHERE
the fronts are, how do we
know what KIND they are?
• It depends on which direction the line
you just drew is moving…
• If colder air is coming in, it is a cold
front.
• If warmer air is coming in, it is a
warm front.
So how do I know which way
the front is moving?
• Look at the winds on both sides of
the front.
• On one side, the winds will be
“pushing” the front.
• On the other side, the winds will be
retreating from the front.
Pop Quiz!
• A pressure center (Low or High) is
located at the “corner” of these two
fronts.
• What kind of pressure center is it?
Almost There!
How do you know if it is a
cold or warm front?
• Put yourself in front of the front.
• Ask yourself: “Self, what kind of air am I
in now: warm or cold?”
• Then ask yourself: “Self, what kind of air
will I be in after the front passes?”
• If it got cooler, it is a cold front.
• If it got warmer, it is a warm front.
I’m in warm air now
Cooler air
Warmer air
Hey it got colder!
It must be a cold front
Cooler air
Warmer air
What about the Eastern
“Leg”?
Cooler air
Boy, it’s pretty cool
Warmer air
It must be a warm front
Cooler air
Warmer air
Aah! Nice and warm.
What kind of weather do you
get from each?
Warm Air
Cool Air
Warm air rises because
it is light & fluffy.
A Cumulonimbus Cloud
“Thunderhead”
Rain
Storms are very
small, 20-50 miles
or so and last
only a brief time.
20-50 miles
Gadzukes! It got
cold!
Right now it’s
nice and warm
Frontal interface
Warm is light and fluffy
and it likes to float!
Warm Air
Cool Air
Warm Air
Cool Air
First come the Cirrus
Which way is the weather coming from?
Such
clouds!
It’s pretty cirrus
cool now
The warm front gets closer…
Hmmm, the clouds are
getting low
Clouds get lower and thicker
Darn! It’s starting to drizzle.
Lower and thicker then
gentle rain for a long time.
It’s much warmer now
3/13/13
• Aim: How do fronts form?
• Do Now:
Based upon the diagram on the board:
A. Which direction is the cold front moving?
B. Which location has the coldest temperature?
C. Which location(s) have precipitation?
D. Which direction is the warm front moving?
• Motivation: Working in groups to complete
lab.
Stationary Front
•
•
•
•
A battle between cold and warm air
When the air masses stop moving they are stationary
The air masses do not mix
Think of an equal match of tug of war
• Cold Front
•
•
•
•
•
•
A cold front is the boundary of a cool dry air mass, most often cP
The arrows point in the direction the front is moving
The air mass is behind the arrows usually cP or sometimes simply P is written
Air temperature is relatively cool
Winds are typically from the NW
The diagram shows a top view (a) and side profile (b)
Stationary front in SE
Occluded Front
• An occluded front is formed when a cold air mass overtakes
a warm air mass
• If a cold air mass overtakes another cool air mass, the
warmer of the two air masses is forced to ascend
• Think of a zipper closing
Middle latitude cyclone aerial view
The cyclone and clouds
Low with clouds
note how clouds are far in advance of the warm front
clouds are localized at the cold front
Notice the clouds swirling toward the low
Map view of cold front chasing warm front
The air mass between the fronts is mT
Behind the cold front is cP
The air in advance of the warm front is relatively cool cP
Cold air intercepts the warm air, contact is made at the ground
 as cold air intercepts warm air, warm air is forced aloft
Rising mT air condenses, latent heat is released rapidly due to convection
Cyclone cross section
occlusion
Cyclogenesis: Stages in the life of a
cyclone
• A cyclone advances and begins to close up
• The shark fin tightens as warm air is forced
up
• Note the differences in the upcoming slides
Low
The cyclone: note the relative positions of the cold and warm front
and the direction they face
Cyclogenesis- a polar front develops a kink when two air masses
collide
Recall P is polar
T is tropical
Cold meets warm air: Stationary front forms
Incipient Wave
Mature stage
Partial Occlusion
Once the cyclone is mature it can begin to “zipper” or occlude
Advanced Occlusion
Warm air lifted off ground
Storm begins to weaken
Cyclone family
Animations
• http://www.mesoscale.iastate.edu/agron206/animations/05
_cnWfronts.html
• http://serc.carleton.edu/NAGTWorkshops/visualization/col
lections/weather_fronts.html
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/fpr.rx
ml
• http://ww2010.atmos.uiuc.edu/(Gl)/guides/mtr/af/frnts/wfr
nt/prcp.rxml
• http://www.classzone.com/books/earth_science/terc/conten
t/visualizations/es2001/es2001page01.cfm?chapter_no=vis
ualization
Lake Effect Snow
• The weather near a lake is affected by the
relatively warm moist air released by lake
waters
Lake Effect Diagram
Snowbelts
Isolines for snowfall
Great Lakes
Lake Effect Animation
NYS aerial
• GO OVER: Sea Breeze & Land Breeze
• Sea Breeze
• Land Breeze