Oral Exam: Weather Information Flashcards
Explain the air flow characteristics of high and low pressure systems in the Northern Hemisphere…
Low Pressure: Air flows inward, upward, and counter-clockwise.
High Pressure: Air flows outward, downward, and clockwise.
What kind of weather is expected if flying towards a low pressure system?
A low pressure system is characterized by rising air, which is conducive to cloudiness, precipitation, and bad weather…
What kind of weather is expected if flying towards a high pressure system?
A high pressure system is characterized by descending air, which tends to favor the dissipation of cloudiness and overall good weather.
Describe a Cold Front…
-Cold Front: occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air.
Describe an Occluded Front…
-Occluded Front: A frontal occlusion occurs when a fast-moving cold front catches up with a slow-moving warm front (warm and cold front occlusions exist)
Describe a Warm Front…
-Warm Front: The boundary area formed when a warm air mass contacts and flows over a colder air mass.
Describe a Stationary Front…
-Stationary Front: When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.
What kind of weather would a pilot experience near a cold front?
As the cold front passes, expected weather can include towering cumulus or cumulonimbus clouds, heavy rain & lightning, thunder and or hail, possible tornados…
-Poor visibility, variable and gusting winds, rapidly dropping barometric pressure and temperature/dew point.
What kid of weather would a pilot experience near a warm front?
As the warm front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility, variable winds and a rise in temperature.
What is a trough?
A trough(line) is an elongated are of relatively low atmospheric pressure.
- It is essentially an area of rising air.
- When air converges at the surface in a low pressure system, it cannot go outward against pressure gradient or down to the ground so it must ascend.
- Rising air in a low pressure system is conducive to cloudiness and precipitation(bad weather)
What is a ridge?
A ridge(line) is an elongated are of relatively high atmospheric pressure. Air moving out of a high/ridge depletes the quantity of air.
- Therefore these are areas of descending air.
- Descending air favors the dissipation of cloudiness (good weather)
What are standard pressure and temperature at sea level?
15* C and 29.92”Hg
What are isobars?
An isobar is a line on a weather chart which connects areas of equal/constant barometric pressure.
When isobars are relatively close together on a surface weather chart or constant pressure chart, what is indicated?
When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds.
-a shallow pressure gradient exists when isobars are not close together and indicates the wind speeds will be less.
What causes the winds aloft to flow parallel to the isobars??
The Coriolis force causes winds aloft to flow parallel to the isobars.
Why do surface winds generally flow across the isobars at an angle?
Surface friction causes winds to generally flow across isobars at an angle.
At what rate does atmospheric pressure decrease with an increase in altitude?
Pressure decreases at a rate of 1”Hg for every 1,000 feet increase in altitude.
What does dew point mean?
Dew point is the temperature at which a sample of air must be cooled to in order to attain a state of saturation….
When temperature and dew point are close together (within 5*) what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog are likely when dew point and temperature converge.
-These conditions are ideal for carb icing too!
What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere determines the type and vertical extent of clouds!
What is the difference between a stable atmosphere and an unstable atmosphere?
The stability of an atmosphere depends on its ability to resist vertical motion….
-In a stable atmosphere, vertical movement is difficult. Small vertical disturbances dampen out and disappear.
-In an unstable atmosphere, small vertical disturbances become larger resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and severe weather.
What are some STABLE atmospheric conditions?
- Stratiform Clouds
- Smooth air
- Steady precipitation
- Fair to poor visibility
What are some UNSTABLE atmospheric conditions?
- Cumuliform Clouds
- Rough air/turbulence
- Showery/off&on precipitation
- Good visibility
How thick should you expect the clouds to be when experiencing significant precipitation at the surface?
Significant precipitation usually requires clouds to be at least 4,000 feet thick… The heavier the precipitation, the thicker the clouds are likely to be.
During preflight planning, what weather information should you be aware of in regards to icing?
- Location of fronts: A front’s location, type, speed, and direction of movement.
- Cloud layers:The location of cloud bases and tops in order to determine if you will climb above icing layers or descend beneath those layers into warmer air. (use PIREPs and area forecasts)
- Freezing levels: Important when determining how to avoid icing and how to exit icing conditions if encountered
- Air temperature and pressure: Icing tends to be found in low-pressure areas and at temperatures at or around freezing.
Define freezing level and how do you determine where it is?
The freezing level is the lowest altitude in the atmosphere over a specific location at which the air temperature reaches 0*C.
- Multiple freezing layers can occur if a temperature inversion exists above the defined freezing level.
- Use current icing products (CIP), forecast icing products (FIP), & freezing level graphics chart to determine the approximate freezing level.
- Other sources of icing information are area forecasts, PIREPs, AIRMETs, SIGMETs, surface analysis charts, low-level significant weather charts, and winds&temperatures aloft…
What conditions are necessary for structural icing to occur?
Structural icing occurs when flying through visible moisture and air temperatures at or below freezing.
What types of icing can a pilot encounter while flying?
Structural, induction system, and instrument icing.
What is clear ice?
-Clear Ice: forms after rain impacts the plane and liquid flows out over the surface. It freezes gradually as a smooth sheet of solid ice.
What is Rime Ice?
-Rime Ice: forms when droplets are small like those found in stratified clouds or light drizzle. The portion of drops remaining after impact freeze rapidly before the liquid has time to spread out over the aircraft surface.
What is Mixed Ice?
-Mixed Ice: Forms when drops vary in size or when liquid is mixed with snow and ice particles. The ice particles become imbedded in clear ice, causing a very rough accumulation.
What action is recommended if you encounter icing conditions?
You should leave the area of visible moisture immediately. Descend to an altitude below the cloud bases or climb to an altitude above the cloud tops, or turn to a different course.