Download Air Masses, Fronts and Storms

Air Masses, Fronts and Storms
Pages 670-673
Air Mass
An _________ ___________ is a large body of air that sits over an area a
long time.
 It sits there long enough to take on the
_____________________ of the area.
The names are a combination of letters that
tell ____________________ they formed
1st over land or sea
 continental ©
 maritme (m)
nd
2 approximate latitude
 artic (a)
 polar (p)
 tropical (t)
General Characteristics
 Maritime will be ___________________
 Continental _________________________
 Maritime and tropical are abbreviated with __________________letters
 Arctic will be ______________
 Polar _____________ ________________ as cold
 Tropical ______________________
Continental Polar (cP)
Source
 Formed over continent
 Near poles
Characteristics
 Cold
 Dry
 Surface type lowercase
letter
 m maritime
 c continental
 Source region is uppercase
 A arctic
 P polar
 T tropical
What will the characteristics of these air masses be? 8 points
 mA

cA

cT

cP
Maritime Tropical (mT)
________________
 Near equator and over water
________________________
 Warm
 Moist
Wrap Up Characteristics
 cP continental polar
 cold, dry, stable
 cT continental tropical
 hot, dry, stable air aloft--unstable surface air
 mP maritime polar
 cool, moist, and unstable
 mT maritime tropical
 warm, moist, usually unstable
Continental polar and continental arctic produce cold _______________ winters
Maritime polar and maritime arctic pick up moisture and bring cool
_________weather
Fronts
Fronts form where air masses ________________
 They are named for the ___________________
 Cold front
 ______________ air invades warm air
 Warm front

______________ air invades cold air
 When the two masses meet, the differences in temperature, moisture and
pressure can cause one air mass to ________________________ the other.
Other fronts
 If neither air mass is moving a _______________________ front
 If a cold front ________________ a warm front it is an occluded front
We find a variety of weather at fronts
 Fronts are accompanied by _____________, __________, __________
and ________________.
Approaching warm front
 Less dense air gradually rises over the cold denser air
 Less obvious and more gradual than cold front

Cirrus clouds

Thicken into altocumulus and altostratus

Sky turns gray

Light to moderate rain or snow develops

At front rain or snow turns to drizzle
I. Atmospheric Lifting
For clouds to form air must ___________________________
 3 lifting mechanisms
1.
2.
3.
I. Convectional Lifting
 Some areas of Earth's surface pick up heat better than others.
 As air warm it becomes less _______________ and rises. As it rises it cools
and sinks
Circulatory motion is called convectional lifting
 If cooling occurs close to the air's saturation temperature, condensing
moisture forms a cumulus cloud
 Form and dissipate over the same area
II. Orographic Lifting
 An air mass is lifted when it is pushed _________________over an obstacle
such as a _______________________ range
 As rising air cools______________ stratus
 If unstable air cumulus
As air moves down the other slope it warms
The Name of the Wind is _____________________
The descending air is dry because the moisture was removed on the other
side.
This is called the _____________ __________________ _______________.
 Example: Eastern Colorado and western Kansas
 See figure 27.10
III. Frontal Lifting
 When fronts collide warm less ______________ air is ________________up
over cold dense air
Thunderstorm Formation
 As cold air pushes into warm moist air, the cold more dense air stays low and
the warmer less dense air is pushed up _______________
 This rapid upward movement forms _______________________
Fronts—dryline

The source region for cT air is the desert Southwest, the high plains
and Mexico with relation to the United States. The air has low
dewpoints and warm to hot afternoon temperatures but with mild
nighttime temperature. Skies are generally clear in cT air. This
allows daytime heating during the day and radiational cooling at
night. The cT air mass is most prevalent in summer; in the cool
season it is not as discernible. Due to the buoyancy and elevation of
cT air across North America, this air will advect into the mid-levels
of the atmosphere once it moves out of its source region. This
creates a cap of mild dry air. If this air advects over PBL mT air, the
severe thunderstorm threat increases significantly. The boundary of
cT is most noticeable with the creation of a dryline. A dryline
separates mT air from cT air. Depending on the strength of the
dryline, convergence along the dryline and the dynamics above the
dryline, severe thunderstorms can form near a dryline boundary.
Hail Formation
 Hail stones form by ____________________
 Small hail gets caught up in the updraft and goes to the top of the cloud
where it receives another _________________ of ice
 This repeats until the hail cannot be _______________________ by
the _______________ and it falls
Hail requires strong _____________________ to form
 For the smallest hail to form, an updraft of around 36 to 54 km/h (24-34 mph)
is required.
 golf-ball size (1 3/4 inch diameter) -- require updrafts of around 88 km/h (55
mph) to form.
 Softball-size hail involves updrafts exceeding 160 km/h (100 mph).
Record Hail
 Record hail fell in Coffeyville, KS
 diameter 14.4 cm (5.67 inches)