Weather Flashcards
Characteristics of stable air
Stratiform clouds
Smooth turbulence
Steady precipitation
Fair to poor visibility
Characteristics of unstable air
Cumuliform clouds
Rough turbulence
Showery precipitation
Good visibility
Low pressure system
Rising air
Conducive to cloudiness, precipitation and bad weather
High pressure system
Descending air
Dissipation of clouds
Good weather
Cold front
Occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air.
Occluded front
A fast moving cold front catches up to a slow moving warm front.
The warm front rises above
Warm front
The boundary area formed when a warm air mass contacts and flows over a colder air mass
Stationary front
Forces of two fronts are relatively equal. Mixture of warm and cold fronts, can influence local weather for a few days
What is dew point?
Dew point is the temperature to which air must be cooled to reach saturation
Characteristics of a cold front
Towering cumulus or cumulonimbus clouds
Heavy rain and lightning
Thunder or hail - tornadoes possible
Poor vis
Winds variable and gusting
Temp/dew point, barometric pressure drop rapidly
Characteristics of a warm front
Stratiform clouds
Drizzle
Low clouds and poor visibility
Variable winds
Rise in temperature
What is a trough?
Elongated area of low pressure
Orange on wx chart
What’s a ridge?
Elongated area of high pressure
What is a microburst?
Small scale intense downdrafts which spreads outward in all directions when it reaches the surface.
Can be found almost anywhere there is convective activity
Less than 1 mile in diameter as it descends from the cloud base
As strong as 6,000fpm
Can extend 2.5 miles near ground level
Seldom last longer than 15 minutes
Can result in wind shear
What is wind shear?
Sudden change of wind velocity and direction
Most often caused by microbursts, temp inversions, and surface obstructions
How far should you avoid a thunderstorm?
20 miles or greater.
You can encounter hail and violent turbulence within 20 miles of a strong storm
Convective SIGMET
Issued hourly at 55 minutes past the hour. Valid for 2 hours
Severe T storms
Surface winds greater or equal to 50kts
Hail at surface greater than 3/4 inch
Tornadoes
Embedded t storms
Always implies severe or greater turbulence, severe icing, or wind shear
SIGMET
Max forecast of 4 hours
Non convective activity
Severe icing not associated with t storms
Clear air turbulence
Dust storms, sand storms leaving vis below 3 miles
Volcanic ash
AIRMET
Can affect all aircraft but but potentially hazardous to to aircraft with limited ability
Valid for 6 hours
Tango - turbulence, sustained surface winds of 30kts or greater. Low level wind shear
Sierra - IFR conditions or mountain obscurations
Zulu - icing and provides freezing level heights
PIREP (UA)
Urgent PIREP (UUA)
Pilot weather reports
METAR
Surface weather observations.
Scheduled METAR’s published every hour
Non scheduled (SPECI) are issued when there is one of more significant change in previous METAR
TAF
Terminal Aerodrome Forecast
Forecast for 5sm around the station.
Issued 4 times a day every 6 hours and normally cover a 24-30 hour period
Standard day
15 Celsius
29.92
What is the standard lapse rate?
2 degrees Celsius per thousand feet
Conditions necessary for formation of thunderstorm:
Sufficient water vapor (humidity)
An unstable temperature lapse rate
Uplifting action
Life cycle of a thunderstorm
Cumulus stage - lifting action, storm starts to grow
Mature stage - precipitation falls from cloud base. Updrafts and downdrafts
Dissipating stage - strong downdrafts and cell is dying rapidly
What is fog?
A cloud that begins within 50 feet of the surface.
It occurs when the air temperature near the ground reaches its dew point, or when the dew point is raised to the existing temperature by added moisture to the air.
What are the types of fog?
Radiation
Advection
Ice
Steam
Upslope
Radiation fog
Occurs at calm clear nights when the ground cools rapidly due to the release of ground radiation
Advection fog
Warm, moist air moves over a cold surface.
Winds are required for advection fog to form.
Ice fog
Forms when temp is much below freezing and water vapor turns directly into ice crystals
Upslope fog
Moist, stable air is forced up a terrain slope and cooled down to its dew point by adiabatic cooling.
Steam fog
Cold, dry air moves over warm water. Moisture is added to the air mass and steam fog forms
Structural ice
Two conditions for formation
Visible moisture (clouds, fog, precipitation)
Aircraft surface temperature below freezing
Clear ice
Most dangerous. Heavy, hard and difficult to move.
Caused by large supercooled water droplets near freezing point
Freezes as smooth sheet of ice
Rime ice
Opaque, white, rough ice, formed by small supercooled water droplets freezing quickly
Occurs at lower temps than clear ice
Mixed ice
Clear and rime formed simultaneously
Instrument ice
Structural ice forming over aircraft instrument and sensors
Pitot and static
Induction ice
Ice reducing the amount of air for the engine intake.
Intake ice - blocks engine intake
Carburetor ice - may form due to steep temp drop and carburetor Venturi
How do you get carburetor icing?
Caused by temperature drop in the carburetor, as an effect of fuel vaporization, and the temperature drop associated with the pressure drop in the Venturi.
Temps between 20-70 Fahrenheit are most conducive to carb icing
What is frost?
Ice crystals caused by sublimation when both the temperature and dew point are below freezing.
Degrades aircraft performance by 30-40%
