JX102 Frontal Mechanics

Question 1

Define Air Mass

Answer 1

An air mass is a large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane (no abrupt temperature and dew point changes within the air mass at a given altitude).

Question 2

What are the differences between moist and dry air masses?

Answer 2

Moist air masses have a greater potential for producing clouds and precipitation than dry air masses.

Question 3

What defines an air mass’s stability?

Answer 3

Temperature; warm air masses brings stable conditions while cold air masses are inherently unstable.

Question 4

Define a Front

Answer 4

A front is an area of discontinuity that forms between two adjacent contrasting air masses; boundary between two air masses.

Question 5

Describe the difference between a surface front and a frontal zone

Answer 5

Surface front: point where a front comes in contact with the ground. Frontal zone: the area that encompasses the weather on either side of the front.

Question 6

What are the 3 characteristics of fronts?

Answer 6

Fronts are always located in a trough of low pressure; Cold fronts generally move faster than warm fronts; Frontal passage usually is accompanied by a 90 degree shift in wind direction.

Question 7

What properties are used to locate and classify fronts?

Answer 7

Temperature, moisture (dew point), winds, and pressure.

Question 8

In respect to temperature, how can it be an indicator of frontal intensity?

Answer 8

The amount and rate of temp change; strong fronts = abrupt, weak fronts = gradual

Question 9

In respect to dew point, how can it help locating the position of a front?

Answer 9

Higher dew points indicate a greater amount of moisture available to produce clouds, fog, or precip.

Question 10

What is a major factor in determining weather associated with a front? What’s another factor?

Answer 10

Moisture available (dew point); speed of frontal movement: faster the movement accompanied by a narrow band of more severe weather, slower moving fronts accompanied by less severe weather (frontal zone more extensive)

Question 11

Which clouds produces steady precipitation and little or no turbulence?

Answer 11

Stratiform clouds

Question 12

Which clouds bring showery precipitation and turbulence?

Answer 12

Cumuliform clouds

Question 13

What kind of frontal slope tends to produce extensive cloudiness with steady precipitation?

Answer 13

Shallow frontal slopes

Question 14

What kind of frontal slope moves rapidly, producing narrow bands of cloudiness and showery precipitation, and normally separates air masses of vastly different properties, indicating potential for more severe weather?

Answer 14

Steep frontal slopes

Question 15

The greater the contrast in temperature and moisture between two air masses, the greater the _________ associated with a front.

Answer 15

Possibility of weather (particularly severe weather)

Question 16

Define a Cold Front

Answer 16

The leading edge of an advancing cold air mass; overtaking cold air is more dense than warm air, wedging under a less dense warm air mass.

Question 17

Describe the wind shifts of a cold front

Answer 17

Approximately 90 degrees from SW to NW

Question 18

Fast-moving cold fronts vs. slow-moving fronts

Answer 18

Fast-moving cold fronts = narrow band, usually severe, and clears rapidly behind the front; slow-moving cold front weather = large area, less severe, but may persist for hours after the front has passed.

Question 19

Define a squall line and identify it’s traits

Answer 19

A squall line is a line of violent thunderstorms; dashed/double dotted purple line; develop 50-300 miles ahead of the cold front and parallel to it; does NOT have to be associated with a cold front

Question 20

Define a Warm Front

Answer 20

The boundary of an advancing warm air mass that is overtaking and replacing a colder air mass

Question 21

Describe characteristics of a warm front

Answer 21

Warmer, less dense air rides up and over top of colder air, squeezing it out; creates broad area of cloudiness, steady precipitation, and reduced visibility; extends 500-700 miles ahead of front’s surface position; slower and produces a more gradual frontal slope, toward and ahead of the surface front

Question 22

Describe the wind shifts of a warm front

Answer 22

From SE to SW

Question 23

Define a Stationary Front

Answer 23

A front where the frontal border between air masses shows little or no movement, with neither air mass replacing the other; weather conditions similar to warm front, but less intense

Question 24

Describe the wind shifts of a stationary front

Answer 24

Surface winds tend to run parallel on both sides of the front; it has a 180 degree wind shift

Question 25

Define an Occluded Front

Answer 25

Fronts that form when a faster moving cold front overtakes a slower moving warm front; two types: cold and warm

Question 26

What determines weather an occluded front is cold or warm?

Answer 26

The type of occluded front depends upon which front remains in ground contact

Question 27

Describe the wind shifts of an occluded front as well as the weather conditions

Answer 27

Wind shift across either type will be 180 degrees; the most severe weather is generally located in an area 100 miles south to 300 miles north of the frontal intersection

Question 28

Define an Inactive Front

Answer 28

Fronts in which clouds and precipitation are not present; aka “dry fronts,” as sometimes the warm air mass is too dry for clouds to form even after the air is lifted and cooled

Question 29

What parameters of an air mass are generally uniform when measured across a horizontal plane?

Answer 29

Temperature and moisture

Question 30

How do the winds shift during a cold front passage?

Answer 30

SW to NW

Question 31

Squall lines generally develop where?

Answer 31

50 - 300 miles ahead of the cold front

Question 32

How far ahead of a warm front can the associated cloud system reach?

Answer 32

500 - 700 miles

Question 33

When encountering a stationary front, you can expect a _____ degree wind shift since surface winds tend to blow parallel on both sides of the front

Answer 33

180

Question 34

When flying through an occluded front, you can expect weather associated with _____ fronts

Answer 34

both cold and warm

Question 35

The most severe weather with respect to an occluded front is generally located _____ NM south to _____ NM north of the frontal intersection

Answer 35

100; 300

Question 36

A(n) _____ front usually has no clouds or precipitation

Answer 36

Inactive

Question 37

The area that encompasses the weather located on either side of a front is called the

Answer 37

Frontal zone

Question 38

Every front is located in a

Answer 38

low-pressure trough

Question 39

Which frontal system has a steeper slope?

Answer 39

A cold front

Question 40

A line of violent thunderstorms that forms ahead of a cold front is known as a

Answer 40

squall line

Question 41

How does the wind normally shift with the passage of a warm front?

Answer 41

SE to SW

Question 42

What type of weather is usually associated with a stationary front?

Answer 42

Weather similar to a warm front, but usually less intense