Weather (Fronts)

Where is the snowfall typically the heaviest with respect to a winter cyclone track?

150 miles to the north of the storm track - because the air is being sucked around and being turned around the surface low

in equal volumes, which one of the following air masses exerts the highest surface air pressure? cP, A, mP, cT, mT

A

cyclones that occur with the greatest frequency over North America are:

Alberta-type

What geographical regions are favored places for cyclogenesis?

Along the rocky mountains and the storms reform and occurs colorado - going up a mountain are large and then on the east side of the mountain come together - tend to see surface low (reintensify) Oklahoma, colorado, wyoming The other type occurs along the gulf of mexico or east coast of america - where you have strong horizontal pressure gradient

major winter storms that affect central IL follow the ____ cyclone track.

Colorado.

Where are the major cyclogenesis regions of North America? How do they vary seasonally?

During the winter, most of the storms are moving through US and during summer they move into Canada and weaken

Occluded front

Life cycle in the surface low - start out in stationary front & a surface low develops along stationary front & when it starts to develop it starts the cyclonic & cold front swings along much faster than warm - both spinning around in a cyclonic direction; the cold front catches up with the warm & forms an occluded --> a hybrid of warm and cold front - with time the occluded front and the cold air is being wrapped around the entire system into the occluded system

Why does a cyclone that moves from Colorado typically have more precipitation than one that develops in Alberta?

Much colder and drier air in Alberta because you’re further from away from a moisture source Colorado bring more humid air and a little bit warmer air (more likely to have snow)

Why is a jet stream usually found above frontal zones?

The contrast between the front of a warm and cold air - the polar front (surface low) because of the disturbance in the jet stream Jet stream forms because of a contrast at the surface

With respect to a wave in the westerlies aloft, where do surface lows and highs most often form and intensify? Explain why these locations are favored. Why do most cyclones develop near the jet stream?

The jet stream has speed divergence you get this region that has horizontal flow at upper troposphere you have surface low will form air to move upward Page 262

Occluded Front

a cold front typically travels about twice as fast as a warm front and eventually may catch up with a warm front to form an occluded front, if the air behind the advancing cold front is colder than the cool air ahead of the warm front, the cold air slides under and lifts the warm air, the cool air, and the warm front.Â

Front

a front is a narrow zone of transition between air masses that differ in density - density differences are usually due to temp contrasts

stationary front

a front that exhibits essentially no movement; parallels the mountain range, can form when any type of preexisting front loses its motion as it becomes parallel to the upper-level flow pattern; can form along a boundary in surface thermal characteristicsÂ

Air Mass

a huge volume of air covering thousands of square kilometers, relatively uniform horizontally in temperature and water vapor concentration, although both quantities typically decrease with altitude

Cold Front

a stationary front becomes a cold front if it begins to move in such a way that colder (more dense) air displaces warmer (less dense) air, the temp contrast across a cold front is typically greater than that across stationary or warm, in summer, air temps on either side of the cold front can be identical, following the passage of a cold front, we normally notice a drop in temp in the winter and a drop in humidity in summer

if a portion of a stationary front between cP and mT air masses moved northward across the midwest, we would classify the frontal boundary asÂ

a warm front

Where does cyclogenesis take place?

along the polar front directly under an area of strong horizontal divergence aloft, this occurs to the east of an upper-level trough & under the left-front quadrant of an upper-level jet streak, if divergence aloft removes more mass from a column of air than is brought in by convergence near the surface, the surface air pressure at the bottom of the column drops & a horizontal pressure gradient develops -- storm is born. the westerly flow aloft then steers and supports the cyclone as it progresses through cycle

how does a cold front surface slope with height?

although friction causes the slope of a warm front to become more shallow, it steepens a cold front close to the earth's surface into a characteristic nose shape, the slope of a cold front is steeper than the warm front, uplift is restricted to a narrow zone at or near the front's leading edge, low-level air motion is quite different from that in warm and stationary, the low-level motion in the cold air is at least in part toward the front and forces the warm air aloft

the type of front formed when the leading edge of cold air merges with a warm front is known as

an occluded front

warm front clouds

as a warm front approaches some locality, clouds develop and gradually lower and thicken in the following sequence: cirrus, cirrostratus, altostratus, nimbostratus, stratus

nocturnal radiational cooling is most intense

at the center of an anticyclone

How are the properties of an air mass determined?

by the type of surface over which it develops, that is, its source region

as a warm front approaches, clouds appear in what sequence?

cirrus, altostratus, stratus

Cold Front

cold air is moving and replacing and denser and moving along at the surface and pushing the warmer air up/air and is replaced by colder, drier, denser air; in that process a lot of times because of the density contrast (warm and humid and most of the time unstable) can kick off thunderstorms after forming cumulonimbus clouds; convective type of clouds!

in winter, continental polar air is ____ maritime polar air.

colder than

of the following air masses, which one exhibits the greatest temp change between winter and summer? maritime tropical, continental polar, maritime polar, equatorial

continental polar

usually air mass modification is most rapid when...

continental polar air moves over bare ground

What are some weather consequences of air mass modification?

cooling leads to condensation or deposition and development of clouds and precipitation, latent heat released during condensation partially offsets adiabatic cooling,Â

a type of cloud associated with a fast-moving, well-defined cold front is:

cumulonimbus

the formation and early development of a midlatitude storm system is called:

cyclogenesis

Continental tropical air (cT)

develops over the subtropical deserts of Mexico and southwestern US primarily in summer and is hot and dry

cold-core anticyclone

dome of continental polar (cP) or arctic (A) air and depending on which air mass type, is labeled either a polar high or arctic high ; product of extreme radiational cooling over the often snow-covered continental interior of north america; shallow systems in which the clockwise circulation weakens with altitude and often reverses; a cold trough is typically situated over a cold anticyclone; produces high surface air pressures because cold air is relatively dense

continental polar air (cP)

dry, develops over northern interior of North America In winter typically very cold because the ground in is source region is often snow covered, days are short, insolation is weak and radiational cooling is extreme In Summer - quite mild and pleasant

Midlatitude cyclone life cycle

early, mature, occluding, occluded

cold fronts typically travel ____ warm fronts.

faster than

source region

features nearly homogeneous surface characteristics over a wide area, such as a great expanse of snow=covered ground or a vast stretch of ocean

Arctic Air (A)

forms over snow- or ice-covered regions, forms in similar ways of Cp but in a region that receives almost no insolation in winter, exceptionally cold and dry and are responsible for the bone numbing winter cold waves that seep across,Â

warm-core anticyclone

forms south of the polar front & consists of extensive areas of subsiding warm, dry air. strengthen w/altitude, massive systems w/a circulation extending from the earth's surface up to the tropopause; may develop over the interior of north america, summer; high surface pressure results from a larger volume of air over the high center - individual layers have the greatest thickness at the center of the high & the intensity of the high increases w/altitude (can become warm cyclones)Â

Halo

have clouds - will start to see optical phenomena; The ring around the moon or the sun are your cirrus clouds (halo) are well in front of a warm front - so you will start to see precipitation within 24-36 hours;

air pollution episodes

high pressure system; associated with an air mass that stagnates over a large urban area

cold outbreaks

high pressure system; associated with the arrival of an A or cP air mass; especially in midlatitudes, causing a marked fall in the air temp

droughts and heat waves

high-pressure system; associated with a stagnant high-pressure system; these situations may appear together or sparately

Warm front

if a stationary front begins to move in such a way that the warm (less dense) air advances while to cold (more dense) air retreats, the front changes in character and becomes a warm front

Squall line

if the cold front moves along at a rapid pace, a squall line, a band of intense thunderstorms may develop

Corona

if you see a corona (water clouds) precipitation is pretty close so within 12-24 hours you will see precipitation; will start to see optical phenomena - corona is associated with water clouds; The ring around the moon or the sun are your cirrus clouds (halo) are well in front of a warm front

surface air pressure drops when horizontal divergence aloft _____ horizontal convergence at the surface.

is greater than

blizzard warning

issued to warn the public of a potentially life threatening winter storm condition with sustained winds or frequent gusts to 35 mph or higher, combined with considerably falling and/or blowing snow, which reduces visibility to less than 0.25 miles. These conditions are expected to last for at least three hours

in a wave cyclone, fog is most likely to develop

just ahead of the surface warm front

an occluded front forms

late in the life cycle of a wave cyclone

In summer, maritime tropical air is ____ continental tropical air.

less dense than

at the center of a polar high, the horizontal pressure gradient is weak and winds are:

light or calm

contrasting air masses are brought together to form fronts by the surface winds about centers of _____ pressure.

low

Warm and humid air corresponds to

mT

Which one of the following air masses is least dense? maritime tropical, arctic, maritime polar, continental tropical, continental polar

maritime tropical

What happens when cP travels over snow-covered ground?

modification is less rapid because much of the incoming solar radiation is reflected, rather than being absorbed and heating the ground, cold surface increases the stability of the air and thereby reduces convection, radiational cooling

how can an air mass become uniform in temp and water vapor concentration?

must reside in its source region for several days to weeks

the cloud and precipitation shield associated with a cold front is typically ____ the cloud and precipitation shield associated with a warm front.

narrower than

precipitation tends to be steady and prolonged in the _____ sector of a wave cyclone.

northeast

the coldest sector of a mature midlatitude cyclone is in theÂ

northwest

Air mass modification

occurs primarily by 1) exchange of heat or moisture, or both, with the surface over which the air mass travels 2) radiational cooling 3) processes associated with large-scale vertical motion

maritime polar air (mP)

over cold ocean waters of the north pacific and north atlantic, along west coast bring, mP air brings heavy winter rains (snows in mountains) and persistent coastal fogs in summer

What types of clouds are associated with a cold front?

pre-frontal: cumulus frontal: Cumulonimbus post-frontal: stratocumulus

what happens when cP air mass crosses the atlantic coast and travels over warm waters of western atlantic?

process of heating from below and destabilization, evaporation from the sea surface increases the water vapor concentration, saturation is easily achieved in the cold and relatively unstable air and leads to extensive low-level cloudiness and fog - cloud streets form

an air mass is characterized by

rather uniform horizontal temp and humidity distributions

a good source region for an air mass would be:

reasonably flat areas of uniform composition with light surface winds

In the southwestern US, heat (thermal) lows generally...

remain stationary

common characteristics of a front

slopes back from the earth's surface toward colder air (more denser air), lies in a tough in the pressure pattern on any horizontal surface intersecting the front

what is the surface wind direction in the warm sector of a mature midlatitude cyclone?

south

the warmest air associated with a mature midlatitude cyclone is usually located

southeast of the low center

a front is a narrow zone of transition between air masses that contrast in

temperature, vapor pressure, density

the term "frontogenesis" refers to a front:

that is strengthening or regenerating

cyclogenesisÂ

the birth of a cyclone, usually takes place along the polar front directly under an area of strong horizontal divergence aloft

a source region for maritime tropical air is

the gulf of mexico

how does a warm front surface slope with height?

the slope of the warm front is shallower near the earth's surface because friction has retarded the front. the airflow on the warm side of the front is quite similar in both instances, but the air on the cold side of the front is retreating in the instance of the warm front

What happens when air moves outside its source region and the polar air is colder than the ground over which it travels?

the sun heats snow free ground, and the warmer ground heats the bottom of the air mass, destabilizing it and triggering convective currents that distribute heat vertically throughout the air mass

the relatively warm side of a storm track is:

to the right of the system's forward motion

associated weather with stationary front

vary considerably from case to case, in cases that do produce precipitation, the rain or snow falls mostly on the cold side of the stationary front, warm humid air flows upward over the cooler air mass, more or less along the frontal surface (overrunning)

Maritime tropical air (mT)

very warm and humid, its source regions are over tropical and subtropical oceans, retains properties year round, responsible for oppressive summer heat and humidity east of Rock Mountains

warm front

warm air lifted upwards and is typically more humid so when it is lifting upwards precipitation forms. You may start seeing fog form in frontal fog especially if you have relatively high humidities - right near the warm front you have frontal fog; have clouds - will start to see optical phenomena; mostly southerly winds for a warm front

warm air advection takes place to the _____ of a ridge and to the _____ of a trough.

west...east

Early cyclone life

when a low-pressure center along with distinct warm and cold fronts being forming

occluding

when the cold front initially catches the warm front, forming the occluded front

mature

when the cyclone has a distinct warm front and cold front separated by a warm sector

occludedÂ

when the occluded front extends outward a considerable distance from the surface low and most of the temp contrasts begin to disappearÂ