Preflight - Fundamentals of Weather Flashcards
At what rate does atmospheric pressure decrease with an increase in altitude?
Atmospheric pressure decreases 1”Hg per 1,000’
What are the standard temperature and pressure values for sea level?
15°C and 29.92” at sea level
State the general characteristics in regard to the flow of air around high and low pressure systems in the northern hemisphere?
Low pressure: Air flows inward, upward, and counterclockwise
High pressure: Air flows outward, downward, and clockwise
If you route of flight takes you towards a low-pressure system, what kind of weather in general can you expect? What if you were flying towards a high-pressure system?
Low-pressure system is characterized by rising air: cloudiness, precipitation, and bad Wx
High-pressure system is characterized by descending air: dissipation of cloudiness and good Wx
Describe the different types of fronts?
Cold: Cold, dense, stable air advances and replaces warmer air
Occluded: fast cold front catches up with slow warm front, (Cold front and warm front occlusion)
Warm: Warm mass contacts and flows over colder mass
Stationary: 2 ≈ air masses remain stationary and last for days (typically mix of warm/cold fronts)
What are the general characteristics of the weather a pilot would encounter when operating near a cold front? A warm front?
Cold Front:
-As front passes: Expect towering cumulus or cumulonimbus, heavy rain, lighting, thunder, hail, or tornadoes
-During passage: Poor visibility, variable/gusty winds, temp/d.p and pressure falling rapidly
Warm Front:
-As front passes: stratiform , drizzle, low ceilings, poor visibility, variable winds, rise in temp
What is a “trough”?
Is an elongated area relatively low pressure, conducive to cloudiness and precipitation
What is a “ridge”?
Is an elongated area relatively high pressure, conducive to good weather
What causes the winds aloft to flow parallel to the isobars?
Coriolis force causes winds aloft to flow parallel to isobars
Why do surface winds generally flow across the isobars at an angle?
Surface friction causes winds to flow across isobars at an angle.
When temperature and dew point are close together (within 5°), what type of weather is likely?
Visible moisture is likely, in the form of clouds, dew, or fog
What factor primarily determines the type and vertical extent of clouds?
Stability of the atmosphere
Explain the difference between a stable atmosphere and unstable atmosphere. Why is the stability of the atmosphere important?
Stability depends on its ability to resist vertical motion.
How do you determine the stability of the atmosphere?
When temperature decreases uniformly and rapidly as you climb (3°C per 1,000’). If temperature remains unchanged or decreases slightly with altitude air is stable. When surface air is warm/moist suspect instability
Lists the effects of stable and unstable air on clouds, turbulence, precipitation, and visibility.
Stable air: Stratiform, smooth, steady precip., and fair/poor visibility
Unstable air: Cumuliform, rough, showery precip., and good visibility
What are the main types of icing an aircraft may encounter?
Structural, induction system, and instrument icing
Name the three types of structural ice that may occur in flight.
Clear icing:Clear or translucent ice from large supercooled droplets. Freezes as it flows over aircraft surface
Rime icing:Rough or opaque ice from supercooled droplets freezing on impact
Mixed icing:Form from a combination of clear/rime ice forming
Describe the types of icing found in stratiform clouds; also in cumuliform clouds.
Stratified clouds: Rime and clear icing
-Icing in Middle/low level usually confined between 3-4,000’ layer
Cumuliform clouds: Clear/mixed and rime in upper levels
-Icing is variable in cumuliform because of the various stages of developement
What is necessary for structural icing to occur?
Aircraft must fly into visible water (rain/cloud droplets) temperature must be at point that strikes the aircraft colder then 0°C
What are the intensity categories of aircraft structural icing?
Trace: ice is perceptible at 1 hour with no deicing equipment
Light: Accumulation could cause a problem after 1 hour without deicing but the deicing will prevent issues
Moderate: Accumulation requires the use of deicing equipment
Severe: Accumulation is too high for deicing
During preflight planning, what type of meteorological information should you be aware of with respect to icing?
Location of fronts:location, type, speed, direction
Cloud layers: bases/tops to know how to get out of icing
Freezing levels: to determine how to avoid icing
Air temperature and pressure: icings tends to be in low pressure areas at or around freezing
Precipitation: Know type/location to be able to avoid
What is the definition of the term “freezing level” and how can you determine where that level is?
Lowest altitude of 0°C, multiple layer can occur with temperature inversion
Can find freezing level in: area forecasts, PIREPS, AIRMETs, SIGMETs, convective SIGMETs, low-level sig. Wx charts, surface analysis, wind/temp aloft
Graphical sources: Current icing product (CIP)/ forecast icing product (FIP)
What are the factors necessary for a thunderstorm to form and what are the three stages of thunderstorm development?
Moisture/unstable lapse rate/lifting force
Cumulus- strong updrafts
Mature- precipitation and downdrafts
Dissipating- downdrafts
What are “squall line” thunderstorms?
Non-frontal narrow band of active thunderstorms
Often develop in front of a cold front
State two basic ways that fog may form?
Cooling air to the dew point
Adding moisture to the air near the ground
Name several types of fog.
Radiation Advection Upslope Frontal/precipitation induced Steam
What causes radiation fog to form?
Clear sky with little wind and small temp/dew-point spread
Almost exclusively at night
What is advection fog, and where is it most likely to form?
Moist air moving over colder ground or water
Requires ≈15 knot winds
Define upslope fog.
Moist stable air, being cooled adiabatically as it moves up terrain
How does steam fog form?
Very cold air moving across warm water
Water vapor rises and condenses to form
Explain hoe frontal (or precipitation-induced) fog forms.
Warm moist air is lifted over front, clouds, and precipitation may form. If cold air below is near dew-point precipitation may evaporate and form fog
Other than fog, what are several other examples of IFR weather producers?
Low clouds, haze, smoke, blowing obstructions, and precipitation
