Weather Flashcards
How does the air flow in low pressure systems?
- Inward
- Upward
- Counterclockwise
How does air flow in a high pressure system?
- Outward
- Downward
- Clockwise
How many types of fronts are there, and what are they?
There are 4 front types
- Occluded Fronts
- Stationary Fronts
- Warm Fronts
- Cold Fronts
What occurs in a occluded front?
A fast moving cold front catches up with a slow-moving warm front.
2 Types:
- Cold Front Occlusions
- Warm Front Occlusions
What occurs in a stationary front?
Two air masses are relatively equal, the boundary/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 type of weather would you encounter in a cold front?
As the front passes expected weather can include:
1. Towering cumulus or cumulonimbus clouds
- Heavy rain accompanied by lightning, thunder and/or hail
- Tornadoes possible
- After passage:
- Good Visibility
- Cooler temperatures
What type of weather can be expected near a warm front?
As the front passes expected weather can include:
1. Stratiform Clouds
- Drizzle
- Low Ceilings
- Poor Visibility
- Variable Winds
- Rise in temperature
Associated weather with a front depends on?
- Amount of moisture
- Degree of stability of the air that is forced upward
- The slope of the front
- Speed of the frontal movement
- The upper wind flow
What is a trough?
Areas of low atmospheric pressure. At the surface, when the low pressure converge, it can’t go outwards against the pressure, or down so it goes upward.
A low/trough is a area of rising air, and rising air is conductive to cloudiness and precipitation.
Hence the general association of low pressure and bad weather
Low pressure is usually associated with what type of weather?
Bad weather
What is a ridge?
An area of high atmospheric pressure (descending air), depleting the quantity of air.
Descending air dissipates clouds and precipitation, hence the general association of low pressure and bad weather.
High pressure systems usually associated with what type of weather?
Good weather.
Downward air pressure gets rid of clouds and moisture, hence the association of high pressure systems, and good weather.
Standard temperature and pressure values at sea level?
59f or 15c and 29.92hg or 1013.2 millibars
What are isobars?
A line on a weather chart which connects areas of equal or constant barometric pressure.
If isobars are close together on a surface weather chart or a constant pressure chart, what info will this provide?
The spacing of isobars on charts defines how steep or shallow a pressure gradient is.
Isobars close together indicate areas of high wind speeds.
A steep pressure gradient (ISO bars close together) indicate what on a surface weather chart?
Higher wind speeds
A shallow pressure gradient (ISO bars not close together) indicates?
Lower wind speeds
Winds flow across isobars at an angle because?
Surface friction
The rate of atmospheric pressure decrease with an increase in altitude?
1” hg / 1,000’
What does the dew point mean?
The temp to which a sample of air must be cooled to attain the state of saturation
When the temp and dew point are close together (within 5 degrees) what type of weather is likely?
- Visible moisture in the form of clouds, fog, dew.
- Ideal conditions for carb icing
What determines the type and the vertical extent of clouds?
The stability of the atmosphere
A stable atmosphere makes vertical movement:
Difficult
Unstable atmosphere, small vertical air movements become:
Larger, resulting in turbulent air and convective activity
Instability can lead to significant turbulence, extensive vertical clouds, and severe weather
What type of clouds are associated with stable air?
Stratiform clouds
What type of turbulence should you expect from stable air?
Smooth
What type of precipitation would you get from stable air?
Steady
In stable air, what type of visibility would you expect?
Fair to poor
What types of clouds are associated with unstable air?
Cumuliform clouds
Turbulence expected from unstable air?
Rough
What type of precipitation would you expect from unstable air?
Showery
What kind of visibility would you get from unstable air?
Good visibility
When there’s significant precipitation occurring at the surface, how thick can you expect the clouds to be?
- Significant precipitation requires clouds to be at least 4,000’ thick
- Heavier precipitation, thicker the clouds are likely to be
What type of meteorological info should you be aware for icing?
- Location of fronts: Location, type, speed and movement
- Cloud layers: location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air’ refer to PIREP’s and forecasts
- Freezing levels: Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered
- Air temp and pressure: Icing tends to be found in low-pressure areas and at temps at or around freezing
What conditions are needed for structural icing to occur?
- Visible moisture
- below freezing temps at the point the moisture strikes the aircraft
2 main categories of icing?
Structural: Refers to the surface components
Induction: Refers to the engine’s induction system
How can you determine where the freezing level is?
- CIP (current icing products) & FIP (forecasting icing products)
- Freezing level graphics charts
- GFA tool
- PIREP’s
- AIRMET’s
- SIGMET’s
- Surface analysis charts
- Low-level SIGWX charts
- Winds and Temps Aloft (for air temp at alt)
What is the definition of the term freezing level?
The lowest altitude in the atmosphere over a given location at which the air temp reaches 0 degrees celsius
- It’s possible to have multiple freezing layers when a temp inversion occurs above the defined freezing level
3 Types of icing that may occur during flight
- Rime Ice
- Clear Ice
- Mixed Ice
What’s Rime icing?
Forms when drops are small (from stratiform clouds) or light drizzle freeze before they spread out over the surface
What is clear icing?
When a droplet hits the surface, spreads out, then freezes forming a layer of thin sheet ice over the surface
Mixed icing during flight
Forms when droplets vary in size when liquid droplets are mingled with snow or ice particles.
- The particles become embedded in the clear ice, building a very rough accumulation
Does icing change the aerodynamic of the wing?
No. It changes the smoothness of airflow over the wing, causing it to be slower airflow over the surface
Slowing of airflow over an iced surface is dangerous because
It causes an early airflow separation , resulting in a loss of lift. This can also prevent aircraft to become airborne at normal speeds for takeoff
Factors for a thunderstorm to form?
- Sufficient water vapor
- Unstable lapse rate
- Lifting force to start the storm process
3 Stages of a thunderstorm
- Cumulus: Updrafts cause raindrops to increase in size
- Mature: Rain at earth’s surface, if falls through, or immediately beside the updrafts
- Dissipating: Downdrafts and rain start to dissipate
SIGMET’s are issued for conditions affecting the area of at least:
3,000 miles
Non-Convective SIGMET examples:
- Sandstorms/ Dust Storms that lower surface and flight visibility to below 3 miles
- Volcanic ash
- Icing not associated with thunderstorms
Examples of Convective SIGMET’s
- Thunderstorms
- Tornadoes
- Severe Turbulence
- Hail greater than 3/4”
- Wind Gusts greater than 50 kts on the surface
What’s the ceiling of class D airspace?
10,000’ MSL
What’s a ground-based temperature inversion?
- Traps fog, smoke, and other restrictions into low levels of atmosphere. The air is stable, with little or no turbulence
What is a temperature inversion?
An inversion is an increase in temperature with height, as opposed to the normal decrease with height
Temperature inversions are associated with what type of air?
Stable air
What kind of turbulence is to be expected with temperature inversions?
little to none
How does fog form?
Cooling air beyond its dewpoint (creating radiation, advection, or upslope fog)
or
Adding moisture to the air and elevating the dewpoint
(producing frontal fog, or steam fog)
Types of Fog:
- Radiation
- Advection
- Upslope
- Precipitation
- Steam
How does radiation fog form?
Ground cools the adjacent air to the dew point on calm, clear nights
Advection fog forms:
- Warm moist air is blown over a cooler surface
- 15 KTS of wind will make this thicker
- Stronger winds will lift fog into low stratus clouds
Steam Fog Forms:
When dry air moves over warm water, the water conducts warm moist air into the cool air above and creates thick steam fog
Upslope fog forms:
Stable air is being cooled as it moves up sloping terrain
- Once the upslope wind ceases the fog dissipates
- Upslope fog is dense and extends to high altitudes
Define wind shear:
Wind shear is the rate of change of wind velocity (direction and/or speed)
What 3 areas should be of concern to a pilot for wind shear?
- Low-level temperature inversions
- Frontal zones or thunderstorm
- Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation