cold front - leading edge of cold air

denoted with a line and filled blue triangles pointing in the direction of

advance warm front - leading edge of warm air

denoted with a line and filled red semicircles in the direction of advance

Frontsfront - an area between two colliding air

masses

Frontal Lifting

more dense DAR

MAR

lifting condensation level

Cumulonimbus clouds

less densecP is a continental polar

air mass - cold, dry, stablemT is a maritime tropical air mass - warm, humid,

unstable

An advancing cold front

note the steep nature of the front

this is a cP or mP air mass

cirrus clouds signal an

advancing front

air pressure and

temperature at the front line

fall dramatically

this is a mT air mass

heavy rain,

winds

note that cumuliform clouds

develop in this case

An advancing warm front

temperature inversion

often occurs

the active warm air mass slides

over the ‘wedge’ of passive cold

air

note that stratiform clouds develop in this

case

drizzly rain

cirrus clouds signal an

advancing frontnote the

progression of cloud

development

show animations

Polar Front, Jet Streams, and Rossby

Waves

the polar front is the area of contrast between cold polar air and warm subtropical air

Aleutian Low Icelandic Low

Midlatitude Cyclonesthese migrating storm systems have low

pressure cores, converging, ascending air, and they rotate counterclockwise in the NH

show animations

the polar jet stream follows the

edge of Rossby

waves - it meanders between 30-70° N

show animations

Mid-latitude Cyclones

• Also known as wave cyclones due to the undulating nature of frontal boundaries and course of the jet stream

• Form due to the collision of warm and cold air masses

• Different from tropical cyclones• High-speed jet stream winds guide

cyclones along their “tracks”

it takes about a week for this whole

process to occur

the initiation of a cyclone occurs when cold and warm air masses

collide - it requires surface convergence towards a low pressure

area and divergence aloft

eastward of the collision front, warm air moves northward and cold air

moves southward - the beginning of counterclockwise rotation - this

movement draws warm air from the south and cold air from the northcold front

warm front

will winds flowing into the low flow parallel to

the isobars?

A squall line can form when a fast-moving cold front

encounters warm air and violently uplifts it

these frontal clouds are 17,000 m (55,000 ft) high,

and extreme winds and rain are affecting the surface

during this stage of a cyclone’s life cycle, the faster-moving cold front

overtakes the warm front and wedges beneath it (”occluding” or

closing it)

precipitation is heavy to moderate at this

stage

during this stage, there is no more

uplifting of air and the storm gradually

fades

there is still some counterclockwise air flow with light winds

show animations

average cyclone storm tracks follow the sun’s movement in the sky

with the seasons

Good luck on the midterm!