Aviation Weather Flashcards
METAR
METeorological Aerodrome Reports:
- surface weather observation published every hour
- SPECI - non-scheduled METARs published when there is a significant change
TAF
Terminal Aerodrome Forecast:
- Weather forecast for 5 SM radius area around the station
- issued 4 times a day every 6 hours
- covers 24 to 30 hour forecast periods
What is a Surface Analysis Chart? How often is it issued?
- issued every 3 hours, (6 hours for hawaii & tropical regions)
- shows pressure systems
- isobars
- fronts
- troughs & ridges
What are Radar summary charts? How often are they issued?
Issued every hour at H+35. Available 16 or 24 hrs a day
· Echo type
· Precipitation Intensity and intensity trend
· Echo configuration and coverage
· Echo heights
· Echo movement
· Severe weather watch areas
What are Wind & temp aloft forecasts and how often are they issued?
- wind forecasts at altitudes and flight levels
- issued 4 times daily
What is a Convective Outlook (AC)?
- delineates areas forecast to have thunderstorms (convective activity)
-available graphical or textual
- provides a 3 day forecast of convective activity
- Issued:
day 1: 5 times a day
day 2: twice
day 3: once
4 Types of weather briefings (SAOI)
1) Standard - full brief, includes everything
2) Abbreviated - updates previous weather info.
3) Outlook - for departure 6 hours away. includes forecasts for time of flight
4) Inflight- provided by FSS
What is an AIRMET and what are the Types of AIRMETs
AIRMET = weather of lower intensity than of SIGMETs but poses hazardous weather to ALL aircrafts VALID for 6 HOURS
Types:
1) Zulu
2) Tango
3) Sierra
AIRMET (Zulu)
- moderate icing and freezing levels
AIRMET (Tango)
- moderate turbulence winds of 30 kts or greater and low level wind shear
AIRMET (Sierra)
- IFR conditions and or extensive mountain obscurations
What is an SIGMET and when they are issued
SIGMET = non-convective weather hazardous to ALL aircrafts VALID for 4 HOURS
Issued when:
- severe icing NOT associated w/ thunderstorms
- severe or extreme CAT not associated w/ thunderstorms
- Dust storms, sandstorms, lowering surface vis. below 3 sm
Convective SIGMET
- Inflight advisory of convective weather, significant to the safety of ALL aircrafts
- VALID 2 HOURS & updated if there is any signifcant changes or H+55
- Severe thundestorms w/ surface winds 50 kts or greater
- Hail 3/4” or greater in diameter
- Embedded thunderstorms
- Tornadoes
- Line of thunderstorms 60 miles or greater
ASOS
Automated Surface Observation System
updated hourly
AWOS
Automated Weather Observation System
updated every minute
ATIS
Automated Terminal Information System
continuous broadcast of local airport wx updated hourly usually 55 minutes passed the hour
What are the 3 ingredients for a thunderstorm?
1) Visible moisture
2) Unstable temperature lapse rate
3) Uplifting force
What are the 3 stages in a thunderstorm life cycle?
1) Cumulus - lifting action of air begins, strong updrafts prohibit moisture from falling. Approx. 15 minutes after cumulus stage, mature stage starts.
2) Mature - MOST dangerous stage
begins when precipitation (rain or hail) starts to fall, lots of up/down drafts
3) Dissipating - strong downdrafts, cell starts to die off
What are the 5 types of fog? RAISU
1) Radiation - clear calm nights ground cools rapidly, when cooling causes air to reach saturation, fog forms.
2) Advection - warm, moist air moved by wind, over a colder surface, causes air to become saturated
3) Ice - forms when temp. is well below freezing and humidity = 100% ; only in colder regions
4) Upslope - moist, stable air forced up over terrain & cooled down to its dew point by adiabatic cooling
5) Steam - cold, dry air moves over warm water. When water evaporates, it rises and forms steam/smoke.
What are the 3 Types of Icing?
1) Clear (2 deg ~ -10 deg C) Most dangerous
2) Rime (-10 deg ~ -20 deg C)
3) Mixed (-15 deg ~ -20 deg C)
Do we have De-icing or Anti-icing?
Anti-icing, pitot tube & cabin heat to prevent windshield from frosting with ice
What to do when you fly into icing conditions?
1) Pitot heat ON
2) AVIATE and COMMUNICATE for deviation or lower altitude
3) If ATC delays you, declare and emergency and ask for vectors
4) If icing conditions are all around you, land as soon as practicable
What are the 3 Kinds of Icing?
1) Structural: ice accumulating on a/c structure
2) Induction: carburetor icing & airbox icing (when iced over, alternate air door will open and lets unfiltered air in decreasing rpm)
3) Critical Systems - when instruments ice up, pitot etc.
What (2) Anti-Icing measures do we have?
1) Pitot Heat - electrically heated, turn on when below 10 deg C in clouds
2) Windshield defroster - cabin heat pointed at windshield
What De-Icing measures do we have?
None
A/C have: pneumatic boots, weeping wings, bleed air, electrically heated, and electro impulse etc.
What are Isobars?
Lines of same or similar pressure, tells us about the pressure gradient force
What is a pressure gradient force?
change in pressure over a given distance, measured by the space between isobars
closely spaced isobars = strong winds
further spaced isobars = light winds
What are the 4 types of Fronts?
1) Cold front: bad weather, occurs when a mass of cold, dense, and stable air replaces a body of warmer air. B/c the air is so dense it acts like a snowplow, sliding under warmer air & forcing the less dense air aloft. Moves faster than warm fronts. (25 to 30 mph)
2) Warm front: good weather, poor vis. warmer air slowly overtaking the colder air. Brings higher humidity. Depending on the stability of a warm front, after being overtaken by a cold front, if warm front is stable, clouds will form, if air is not stable, thunder storms and squall lines would form.
3) Occluded front: cold front catching up to a warm front. Strong wind heavy precipitation
4) Stationary front: neither air mass overtaking each other hence “stationary”, stationary clouds
How direction does low and high pressure move?
Low = up, inwards, & counter clockwise High = down, outwards, & clockwise
What is Standard Lapse Rate?
Standard:
- 2 deg C per 1,000 ft
- 1” barometric pressure per 1,000 ft
If not standard, this means that there is unstable weather
What is Convection?
high temperatures at the equator leading to rising, less dense air, which flows towards the poles, cools, & becomes dense again, sinks back towards the surface
What is Coriolis Force?
- Rotation of the earth that affects the way air moves
- Moves Right at the Northern Hemisphere
- Moves Left at the Southern Hemisphere
- Strongest at the poles, weakest at the equator
Standard temperature and pressure?
- 15 deg C or 59 deg F
- 29.92” Hg or 1013.25 milibars
- 1.225 kg/m^3 density
Describe the 4 intensities of turbulence
Light - slight changes in attitude & altitudes
Moderate - same as light but a bit worse
Severe - large loss of attitude & altitude, momentary loss of controls
Extreme - violently tossed around, impossible to control, structural damage
What are the 4 types of turbulence?
1) Mechanical - buildings and objects on the ground
2) Clear Air - above 15,000’ associated w/ jetstreams
3) Convective - uneven heating of earth’s surface
4) Frontal - caused by two opposing air masses; associated w/ cold fronts
What are troughs?
elongated area of low pressure, opposite of a ridge (orange dashed lines)
What are ridges?
elongated area of high pressure, opposite of a trough
Cold front
Warm Front
Stationary Front - neither air mass overtaking each other hence “stationary”, stationary clouds
Occluded Front - cold front catching up to a warm front. Strong wind heavy precipitation
Troughs - elongated area of low pressure, opposite of a ridge (orange dashed lines)
Squall line - a line of active thunderstorms
Dry Line - a boundary separating moist and dry air masses.
Tropical Wave - an area of low pressure troughs, moves from east to west. Associated with cyclones and strong wind shears.
What causes Weather?
all weather is the result of differences in temperature, weather is caused by heat exchanges in the atmosphere and the surface, when pressure changes it means that the surface is not heated equally, thus causing weather.
What are the (3) forces that causes wind?
1) Pressure gradient force: rate of change in barometric pressure over a given distance
2) Coriolis force: deflection of the wind to the right (can feel the effects in the northern hemisphere)
3) Surface friction: obstruction to windflow by man made or naturally made obstructions
What is an Air mass?
body of air that has uniform moisture & temperature properties
What is a front?
happens when there is a transition between two air masses that are different in temperture, humidity, and wind.
Decode the following Forecasted Winds Aloft:
731960
189960
751041
771150
2867-21
2842-13
- 731960: 230º @ 119kts (temperature -60º C)
- 189960: 180º @ 200kts+ (temperature -60º C)
- 751041: 250º @ 110kts (temperature -41º C)
- 771150: 270º @ 111kts (temperature -50º C)
- 2867-21: 280º @ 67kts (temperature -21º C)
- 2842-13: 280º @ 42kts (temperature -13º C)
Important info:
- No winds are forecasted within 1,500’ of station elevation
- Winds are forecasted true, indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits)
- 2022: 200@22 knots
- Above FL240 the negative is removed from temperature, it is always negative]
- If forecast speed is less than 5 knots, the coded group is 9900 which means, “light and variable”
- If the wind speed forecast to be 200 knots or greater, the wind group is coded as 99 knots
Significant Weather Prognostic Charts (progs)
Issued – four times daily with 12- and 24-hour forecasts based on 00Z, 06Z, 12Z and 18Z synoptic data.
- 12- and 24-hour forecasts for significant weather from the surface 24,000ft
- used for outlook purposes. Use to get a general picture of the weather conditions that are in the relatively distant future.
Winds and Temperatures Aloft Charts
Issued – daily for 12-hour progs valid at 12Z and 00Z.
Features:
· For altitudes 6000, 9000, 12,000, 18,000, 24,000, 30,000, 34,000 and 39,000 feet MSL
· Shows wind direction and speed
· Shows temperature aloft
What is a standard TEMPERATURE lapse rate? PHAK 4-3
- when temperature decreases at 2º C per thousand ft
up to 36,000 ft. Above 36,000, the temperature is considered constant up to 80,000 ft.
What is a standard PRESSURE lapse rate? PHAK 4-3
- when pressure decreases at a rate of approximately 1” Hg per 1,000 ft of altitude gained to 10,000 ft
What is an Inversion? PHAK 12-13
When temperature of air rises with altitude, a temperature inversion exists. Commonly, shallow layers of smooth, stable air close to the ground. The air at the top of the inversion acts like a lid, keeping weather and pollutants trapped below.
If relative humidity is high, cloud, fog, & haze can form, reducing visibility.
What are the two types of Inversion? PHAK 12-13
Surface based Inversion = occur on clear, cool, nights when the air close to the ground is cooled by the lowering temperature of the ground.
Frontal Inversion = occurs when warm air spreads over a layer of cooler air; or cooler air is forced under a layer of warmer air.
What is meant by unstable air?
Air that, when pushed up, keeps rising. Conversely, stable airresists upward movement.
What are some examples of weather phenomena that can cause a lifting action?
- Orographic effects (wind moving across mountains and valleys)
- Frictional effects (low pressure systems)
- Frontal lifting (when less dense warm air is forced to rise over cooler, denser air as a weather fronts move)
- buoyancy (uneven heating of surface).
What is relative humidity?
indicates how closely the air is to being saturated
What is saturated air?
When a volume of air at a given temperature holds the maximum amount of water vapour, has a relative humidity of 100%
What is dew point?
temperature to which air must be cooled to become saturated without changing the pressure. (The closer the dew point is to the air temperature, the closer the air is to saturation)
What are clouds and how do they form?
- Clouds are composed of particles of liquid water (cloud droplets), and particles of ice called (Ice crystals).
- Clouds are formed when air is cooled and the temperature equals the dew point (100% humidity) resulting in condensation, which produces clouds.
What are the four lifting mechanisms that form clouds? OCCU
O - Orographic (air cannot go through a mountain, so it flows over it)
C - Convection (heating of the surface, causing air to rise)
C - Convergence (air at the surface flows together and pushed upwards)
U - Updraft (rising air from lifting forces)
Describe these types of clouds:
Cirro
Alto
Nimbus
Low
Middle
High
Precipitating
Cirro - high clouds composed of wispy crystals
Alto - cloud in middle of troposphere
Nimbus - cloud associated with precipitation
Low -stratus, stratocumulus, and cumulus clouds
Middle - altostratus and altocumulus clouds
High - cirrocumulus, cirrostratus, and cirrus clouds
Precipitating - nimbostratus and cumulonimbus clouds
Difference between Centrifugal & Centripetal force ?
Centrifugal = outwards
Centripetal = inwards
What are the different types of thundestorms? SMSS
S - Single Cell : form when atmosphere is unstable, short lived & last less than an hour becoming strong enough to produce lightning
M - Multi cell : group of cells merging together, lots of gusts & up/downdrafts
S - Super cell : large severe storms, powerful updrafts, top of clouds can be 15mi wide. Produce destructive tornadoes.
S - Squall Line : lines of multicell storms with gusts, 100+ miles long, associated with high winds, lightning, tornadoes, heavy rain/hail.
What is the difference between fog and cloud?
Clouds and fog both form when water vapor condenses or freezes to form tiny droplets or crystals in the air, but clouds can form at many different altitudes while fog only forms near the ground.
What is considered a ceiling?
the lowest layer of broken, overcast, or obscurated cloud layer. (AGL)
Cool air moving over a warm surface is generally characterized by?
Cool air moving over a warm surface is heated from below, generating instability and showers
Warm air moving over a cool surface is generally characterized by?
Warm air moving over a cool surface is cooled from below, increasing stability. If air is cooled to its dew point, stratus and/or fog forms.
