Weather Ch. 3

Question 1

DEFINE the term air mass

Answer 1

• a large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane
  
  • no abrupt temperature or dew point changes within the air mass at a given altitude
  • may vary in size from several hundred to more than several thousand square miles
• Air masses are named according to their location, moisture content, and temperature. The location of an air mass has a large influence over the other two properties. Naturally, moist air masses will have a greater potential for producing clouds and precipitation than dry air masses. Most importantly, though, its temperature indicates the stability of the air mass. Warm air masses bring stable conditions, while cold air masses are inherently unstable.

Question 2

DEFINE the term front

Answer 2

• an area of discontinuity that forms between two contrasting air masses when they are adjacent to each other
  
  • can be thought of as a border, boundary, or line between the air masses
• air masses must have sufficiently different temperature and moisture properties– the defining characteristics of an air mass–otherwise there would be little reason to distinguish between them

Question 3

DESCRIBE the structure of a front

Answer 3

• 3-dimensional
• can be hundreds of miles long
• The depth of this frontal zone depends on the properties of the two air masses
• When the properties differ greatly, the resulting narrow frontal zone can include sudden and severe weather changes. It is often impossible to determine the exact outer boundaries of a frontal zone
• winds shift 90 degrees

Question 4

DESCRIBE the discontinuities used to locate and classify fronts

Answer 4

• Differences in adjacent airmasses their temperature, moisture (indicated by the dew point), winds, and pressure–are used to locate and classify fronts.
• Cloud types are also useful indicators of the type of front and will be discussed in connection with each individual front

Question 5

DESCRIBE the factors that influence frontal weather

Answer 5

1. The amount of moisture available (shown by the dew point)
   * greatly determines the amount of weather associated with a front. Often little or no significant weather is associated with a front or a portion of a front because of a lack of moisture, despite the presence of all other factors
2. The degree of stability of the lifted air
   * determines whether cloudiness will be predominantly stratiform or cumuliform. With stratiform clouds, there is usually steady precipitation and little or no turbulence. Precipitation from cumuliform clouds is showery and the clouds indicate turbulence.
3. The slope of the front

• slope of a warm front is generally shallow, while the slope of a cold front can be quite steep
• Shallow frontal slopes tend to produce extensive cloudiness with large areas of steady precipitation,
• steep frontal slopes tend to move rapidly producing narrow bands of cloudiness and showery precipitation. Steep frontal slopes normally separate air masses of vastly different properties, indicating the potential for more severe weather

4. The speed of the frontal movement

• Faster moving fronts are generally accompanied by a narrow band of more severe weather
• slower moving fronts have less severe weather, but the frontal zone is more extensive

5. The contrast in the amounts of temperature and moisture between the two air masses
   * The larger the contrast, the more significatn the weather will be

Question 6

DESCRIBE the conditions associated with a cold front

Answer 6

• leading edge of an advancing cold air mass overtaking less dense, warm air
• Cold fronts move toward the SE at 20kts, on average, and the wind shift is from the SW to the NW
• wedge under warm fronts and cause violent thunderstorms
• weather can vary greatly depending on the speed of the front and the characteristics of the air masses
• Narrow forntal zone
• cooler temps and clearing skies after forntal passage

1. outhwesterly winds in the warm air mass ahead of the front begin to increase in speed
2. barometric pressure decreases, and altocumulus clouds appear on the horizon
3. cloud bases lower, and rain or snow showers begin as the cumulonimbus clouds move into the area
4. percepitation increases in intensity and may persist
5. As the front passes, the pressure rises sharply and the wind shifts approximately 90° from SW to NW

Question 7

DESCRIBE the characteristics of a squall line

Answer 7

• Associated with cold fronts
• exact cause unknown
• forms 50-300 miles ahead of cold front
• can form without cold front
• contaions severe hazards to aviation like crazy thunderstorms
• dashed double dotted purple lines on chart

Question 8

DESCRIBE the characteristics of a warm front

Answer 8

• warm fronts advances over dense, cold air
• extensive forward slope
• weather occurs 500-700 nm ahead of surface front
• steady percipitation and reduced visibility ahead of frontal passage
• winds shift SE to SW with frontal passage
• Move NE arounf 15 kts

Question 9

DESCRIBE the conditions associated with a stationary front

Answer 9

• weather similar to warm front
• allign in any direction
• 180 degree wind shift across the forntal boundry

Question 10

DESCRIBE the conditions associated with occluded fronts

Answer 10

• Formed when cold front overtakes warm front
• warm front occlusion= warm front touches ground (15 Knots)
• cold front occlusion= cold front touches the ground (20 Knots)
• purple warm and cold front symbols
• pressure falls then rises
• winds shift from SE to NW with forntal passage

Question 11

DESCRIBE the conditions associated with an inactive front

Answer 11

• dry front
• no clouds or perciptation
• wind shift and temp change still occur
• markes area of potentially unfavorable fling conditions

Question 12

Front Chart

Answer 12