Weather 2: Weather Mechanics Flashcards
What are gradient winds?
- Winds that flow perpendicular to the pressure gradient force and parallel to the isobars of the pressure system
- Found above 2,000’ AGL
What is the flow direction of gradient winds in a low pressure system?
Counter-clockwise
What is the flow direction of gradient winds in a high pressure system?
Clockwise
What forces causes the flow direction of gradient winds?
- Pressure gradient force
- Coriolis force
What are surface winds?
- Winds that flow at a 45° angle across isobars
- Found below 2,000’ AGL
What is the flow direction of surface winds in a low pressure system?
Counter-clockwise around and into the low system
What is the flow direction of surface winds in a high pressure system?
Clockwise around and out of the high system
What forces causes the flow direction of surface winds?
- Pressure gradient force
- Coriolis force
- Surfrace friction
Jet Stream
A narrow band of strong winds of 50kts or more that stays vertically and horizontally around the hemisphere in wave-like patterns (flows west to east)
What are some characteristics of the jet stream? (Average wind speed, average height, segments, thickness)
- Average wind speed: 100-150kts but can reach up to 250kts
- Average height: 30,000’ MSL
- 1000-3000 miles (length)
- 100-400 miles (width)
- 3000-7000 ft (thickness)
Sea breeze
- An onshore wind blowing from sea to land
- Can reach 15-20kts
- Usually occurs during the day
Caused by the warmer air over the land rising (because it is less dense) and the colder air from the ocean moving in and going under the rising warmer air
Land Breeze
- An offshore wind blowing from land to sea
- Usually not as strong as the sea breeze
- Usually occurs during the night
Caused by the warmer air over the ocean rising (because it is less dense) and the colder air from the land moving in
What are the cloud types and their respective altitudes?
- Low Clouds (surface - 6,500’ AGL)
- Middle Clouds (6,500’ AGL - 20,000’ AGL)
- High Clouds (above 20,000’ AGL)
- Special clouds with extensive vertical development
What determines cloud height?
The height of the base of the cloud
What are the cloud forms?
- Cumuliform
- Stratiform
Describe cumuliform clouds.
- Comes from moist, unstable air
- Associated with showery precipitation
- Large puffy clouds with more definite shapes
Describe stratiform clouds.
- Comes from moist, stable air
- Associated with steady precipitation
- Widespread with no definable shape
Describe Special Clouds with Extensive Vertical Development.
Clouds that usually has a base at low/middle cloud height and has tops that extend through high cloud heights
Three main types:
1. Nimbostratus
2. Towering cumulus
3. Cumulonimbus
Describe Low Clouds.
- From surface to 6,500’ AGL
- Mainly made of water droplets
- If you see “nimbo” or nimbus” that means violent/heavy precipitation from these clouds
Describe Middle Clouds.
- From 6,500’ AGL to 20,000’ AGL
- Made of ice crystals, water droplets, or both
- Has the prefix “alto”
Describe High Clouds.
- Above 20,000’ AGL
- Made of ice crystals
- Has the prefix “cirro” or contains the word “cirrus”
What are the characteristics of precipitation?
- Showery
- Continuous
- Intermittent
Describe the following precipitation characteristic: showery.
- Has a sudden beginning and ending
- Abruptly intensity changes
- Associated with cumuliform clouds
Describe the following precipitation characteristic: continuous.
- Steady precipitation with a gradual change in intensity (if any change at all)
- Associated with stratiform clouds
Describe the following precipitation characteristic: intermittent.
- Stops and restarts at least once during the hour
- Associated with cumuliform or stratiform clouds
What are the methods of lifting?
- Frontal
- Orographic
- Convergence
- Thermal
“You’re FOCT’d”
Convergence lifting
When air masses combine and push air upwards
Frontal lifting
When a cold front’s slope lifts the air ahead of the cold air mass
Orographic lifting
When the force of the wind against a mountainside pushes the air upwards
Thermal lifting
When air rises as it is warmed over a surface
What kind of conditions are associated with cumuliform clouds?
Unstable conditions
What kind of conditions are associated with stratiform clouds?
Stable conditions
If the lifted air is colder than the surrounding air, what kind of stability would it be? Why?
Stable
Since the colder air is more dense than the surrounding air, it will settle back down to its original position once the lifting force is removed
If the lifted air is warmer than the surrounding air, what kind of stability would it be? Why?
Unstable
Since the warmer is less dense than the surrounding air, it will continue to rise after the lifting force is removed
If the lifted air is the same temperature than the surrounding air, what kind of stability would it be? Why?
Neutrally Stable
Since the air has the same density, it will settle at whatever point it is at when the lifting force is removed
What are the flight conditions that are associated with a stable atmosphere?
- Warm fronts
- Warm air
- Smooth air (no turbulence)
- Poor visibility
- Rime icing
- Steady winds
- Steady precipitations
- Stratus clouds
“What Would Sarah Palin Repeat, Something Stupid Silly
What are the flight conditions that are associated with a unstable atmosphere?
- Cold fronts
- Cold air
- Rough turbulence
- Good visibility (outside of clouds)
- Clear icing
- Showery precipitation
- Gusty winds
- Cumulus clouds
“Captain Crunch, Really Good Cereal, Super Good Cereal”
Front
An area of discontinuity that forms between two contrasting air masses
What are the frontal discontinuities used to classify fronts?
- Temperature: can indicate intensity of front
- Dew point: indicates RH of the air
- Pressure: decreases as you enter front and increases as you pass through front
- Wind: expect a 90° wind shift
“TouchDowns Win Playoff games.”
Cold front
The leading edge of an advancing cold air mass that slides underneath warm air pushing it upwards and causing unstable conditions, cumuliform clouds, and showery precipitation.
Usually moves towards the SE @ 20kts with a 90° wind shift
The colder, more dense air moves in underneath the warmer air and pushes it upwards
Squall lines
Lines of fast moving thunderstorms
Where do squall lines form?
Often develop 50 - 300 miles in front of cold fronts
How do squall lines form?
When cold air ahead of the cold front downdrafts and lifts additional warm air. This warm air creates it’s own updrafts and downdrafts which start the thunderstorm development cycle
Warm front
The boundary of an advancing warm air mass that is overtaking and replacing a colder air mass
Usually moves @ 15kts with a 90° wind shift from SE to SW
The warmer, less dense air rides up and on top of the cold air mass and creates an area of cloudiness as it moves over the frontal surface
Stationary front
A front in which neither air mass is replacing the other at the frontal border
Has a 180° wind shift
Occluded front
A front where a faster moving cold front overtakes a slower moving warm front
Usually moves at the speed of whatever front is on the ground and has a 180° wind shift
Two types: (1) cold and (2) warm –> named after whichever front remains in contact with the ground
What weather is associated with a cold front?
More severe weather in a narrow band
What weather is associated with a warm front?
Broad cloudiness with a steady precipitation that gradually increases until the front passes
What weather is associated with an occluded front?
Weather from both warm and cold fronts
What weather is associated with a stationary front?
Similar weather to a warm front but at a lower intentsity
