JX102 Frontal Mechanics Flashcards
Frontal Mechanics
Define Air Mass
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).
What are the differences between moist and dry air masses?
Moist air masses have a greater potential for producing clouds and precipitation than dry air masses.
What defines an air mass’s stability?
Temperature; warm air masses brings stable conditions while cold air masses are inherently unstable.
Define a Front
A front is an area of discontinuity that forms between two adjacent contrasting air masses; boundary between two air masses.
Describe the difference between a surface front and a frontal zone
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.
What are the 3 characteristics of fronts?
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.
What properties are used to locate and classify fronts?
Temperature, moisture (dew point), winds, and pressure.
In respect to temperature, how can it be an indicator of frontal intensity?
The amount and rate of temp change; strong fronts = abrupt, weak fronts = gradual
In respect to dew point, how can it help locating the position of a front?
Higher dew points indicate a greater amount of moisture available to produce clouds, fog, or precip.
What is a major factor in determining weather associated with a front? What’s another factor?
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)
Which clouds produces steady precipitation and little or no turbulence?
Stratiform clouds
Which clouds bring showery precipitation and turbulence?
Cumuliform clouds
What kind of frontal slope tends to produce extensive cloudiness with steady precipitation?
Shallow frontal slopes
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?
Steep frontal slopes
The greater the contrast in temperature and moisture between two air masses, the greater the _________ associated with a front.
Possibility of weather (particularly severe weather)
Define a Cold Front
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.
Describe the wind shifts of a cold front
Approximately 90 degrees from SW to NW
Fast-moving cold fronts vs. slow-moving fronts
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.
Define a squall line and identify it’s traits
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
Define a Warm Front
The boundary of an advancing warm air mass that is overtaking and replacing a colder air mass
Describe characteristics of a warm front
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
Describe the wind shifts of a warm front
From SE to SW
Define a Stationary Front
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
Describe the wind shifts of a stationary front
Surface winds tend to run parallel on both sides of the front; it has a 180 degree wind shift
Define an Occluded Front
Fronts that form when a faster moving cold front overtakes a slower moving warm front; two types: cold and warm
What determines weather an occluded front is cold or warm?
The type of occluded front depends upon which front remains in ground contact
Describe the wind shifts of an occluded front as well as the weather conditions
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
Define an Inactive Front
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
What parameters of an air mass are generally uniform when measured across a horizontal plane?
Temperature and moisture
How do the winds shift during a cold front passage?
SW to NW
Squall lines generally develop where?
50 - 300 miles ahead of the cold front
How far ahead of a warm front can the associated cloud system reach?
500 - 700 miles
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
180
When flying through an occluded front, you can expect weather associated with _____ fronts
both cold and warm
The most severe weather with respect to an occluded front is generally located _____ NM south to _____ NM north of the frontal intersection
100; 300
A(n) _____ front usually has no clouds or precipitation
Inactive
The area that encompasses the weather located on either side of a front is called the
Frontal zone
Every front is located in a
low-pressure trough
Which frontal system has a steeper slope?
A cold front
A line of violent thunderstorms that forms ahead of a cold front is known as a
squall line
How does the wind normally shift with the passage of a warm front?
SE to SW
What type of weather is usually associated with a stationary front?
Weather similar to a warm front, but usually less intense
