Meteorology Flashcards
(177 cards)
1
Q
Layers of the atmosphere
A
From ground level:
i) Troposphere
- Tropopause
ii) Stratosphere
iii) Mesosphere
iv) Thermosphere
2
Q
3 differences between troposphere and stratosphere
A
- Temperature declines with altitude in troposphere, constant -57 deg C in stratosphere
- Troposphere has vertical movement of air (hot/cold), stratosphere not as much
- Stratosphere has very limited water vapour so generally clear of cloud
3
Q
Height of tropopause
A
20,000 ft at poles
36,000 ft assumed under ISA
60,000 ft at equator
4
Q
Capacity of air to carry water with temperature
A
Hotter air can hold more water than colder air
5
Q
ISA conditions at sea level
A
- 1013.25 hPa
- 15 degC
- 1.225kg/m3 density
- no water content
6
Q
ISA conditions as altitude changes
A
- 2 degC lower per 1,000 ft
- 1hPa lower per 30ft
7
Q
Synoptic situation
A
The high level weather situation (e.g. areas of high and lower pressure)
8
Q
Standard barometer type
A
Aneroid - Partially evacuated flexible metal chamber
9
Q
Diabatic vs adiabatic processes
A
Diabatic processes involve heat exchange between two bodies or redistributed in one body.
Adiabatic process (e.g. compression of gases) include temperature change but no exchange of heat.
10
Q
List of diabatic processes
A
- Radiation
- Absorption
- Conduction
- Convection
- Advection
11
Q
Which bodies emit radiation?
A
All objects emit radiation.
12
Q
What is advection?
A
When cool air is drawn into an area to replace warm air that has risen due to convection
13
Q
Definition of heat capacity
- water vs land
A
The amount of energy required to heat 1kg of a material by 1 degree C
- water has higher heat capacity than land (so land heats and cools more quickly)
14
Q
Emissivity of a surface
- water vs land
A
The propensity of a surface to emit radiation.
Land typically has less emissivity than water.
15
Q
ELR
- Stands for
- Definition
A
Environmental Lapse Rate
The true rate at which the atmosphere loses temperature as altitude rises, based on weather conditions on the day
16
Q
DALR
- Stands for
- Definition
A
Dry Adiabatic Lapse Rate
A dry parcel of air behaves adiabatically and cools at 3 degrees C for each 1,000ft it rises
17
Q
SALR
- Stands for
- Definition
A
Satiated Adiabatic Lapse Rate
Water vapour in rising air that cools to dewpoint will condense and release latent heat energy. Therefore satiated air cools at around 1.5 degrees C per 1,000ft (but highly variable).
18
Q
Impact of ELR
A
ELR < SALR => Stable. Air tends to return if displaced (e.g. clear air, fog)
ELR > DALR => Unstable. Air tends to rise if displaced (e.g. cumulus or cumulonimbus cloud)
SALR < ELR < DALR => Dry air is stable, moist air is unstable
19
Q
Temperature Inversion
A
When land is cold (e.g. clear night, heat lost through radiation) the air around it cools and stays below hotter air higher up. This “inversion” of normal pattern can cause fog, stratus or windshear
20
Q
Cause of high level (5000ft) inversion
A
Descending air at high level will warm as it falls, trapping cooler air below
21
Q
Isothermal layer
A
Layer where air temp is the same
22
Q
Stratus
A
Low altitude clouds
23
Q
General Circulation Pattern
A
Repeated on each hemisphere
- Tropical cell: air rises near equator heads to pole at high altitude and loops back at sea level to equator.
- Polar cell: cool air sinks and is drawn towards equator, rises at polar front and loops around at high altitude.
- Mid-latitude cell: sits in-between, air rises near polar front and falls near tropical cell to match their directions.
24
Q
Arctic vs Polar cell
A
Arctic is higher, separated from polar cell by arctic front.
Polar cell comes next, separated from warm mid-latitude air by polar front.
25
Equatorial trough
The low pressure band of air near equator caused by rising hot air.
26
Convergence vs divergence at equator and poles
Convergence is when surface air is drawn into the equatorial trough.
Divergence is the opposite at the poles, high-pressure cooled air spreads outwards.
27
Relationship between celsius and farenheit
0 C = 32 F
100C = 212 F
F = (9/5) * C + 32
28
Wind directions true or magnetic?
Weather forecasts refer to true bearings.
ATC (and ATIS) will refer to magnetic bearings to help relate to runway direction.
29
Veering vs backing
Veering means wind direction heading is increasing, backing means heading is decreasing.
30
Two forces causing wind
Pressure Gradient Force
Coriolis Force
31
What is coriolis force?
Air rotates along with the earth's rotation. However speed of rotation changes at different latitudes. As air moves north or south it will have a higher or lower easterly speed than the earths rotation creating east/westerly wind speed component.
32
Relationship between coriolis force and wind speed
Higher windspeed results in higher coriolis force
33
Which latitudes have highest coriolis force?
Higher coriolis force at higher latitudes as the change in speed of the earth over a given latitude change is higher closer to the poles.
34
Which way does coriolis force affect wind direction?
To the right in Northern hemisphere, to the left in Southern.
35
Geostrophic wind
This is the balanced steady wind state.
Over time the coriolis force will turn the wind created by pressure gradient so that it is parallel to the isobars (low pressure on the left in NH).
Wind strength will be proportional to the pressure gradient.
36
Buys Ballot's Law
In Northern Hemisphere, if you stand with back to the wind, low pressure will be on your left.
37
Implication of Buys Ballot's law
If flying with a starboard drift, wind is on your left so flying into low pressure. This means bad weather and ground clearance issues if you don't reset pressure setting.
Port drift means heading to higher pressure, better weather and more ground clearance.
38
Is low or high pressure system more stable?
High pressure system is more stable, more vertical air movement in low pressure systems.
39
Cyclone and anti-cyclone
Circular isobar patterns have either a high or low at the centre. In NH, low pressure system goes anti-clockwise (cyclonic motion), high pressure system goes clockwise (anti-cyclonic system).
40
Balance of forces in cyclones and anti-cyclones
Circular wind velocity requires acceleration (centri-petal) force towards the centre of the circle.
This means that in cyclonic (low pressure) system, pressure gradient force is greater than coriolis force, and opposite in anti-cyclonic.
41
Point at which surface wind is measured
10 metres above surface, around where wind socks will be
42
Top of boundary layer
Point where frictional forces of ground have negligible impact on wind, around 2000 to 3000 ft
43
Coriolis force close to earth and above boundary layer
Lower wind speeds near surface will reduce coriolis force making pressure gradient the major factor.
Around the top of the boundary layer wind will be flowing parallel to isobars.
44
Does wind veer or back as a result of surface friction?
Surface wind is slower due to friction and coriolis force increases with wind speed, so is lower at the surface.
Thus, in NH the wind backs close to the surface due to weakening coriolis effect.
45
Expected landing direction based on wind experienced at 2000ft
Expect wind to back close to the ground, so runway might be 30 or so degrees less than wind direction at altitude.
46
Factors affecting level of surface friction
Wind speed reduction and degree of backing affected by terrain (sea has less friction than land) and atmospheric stability (more stable means less vertical movement and thus less high altitude wind speed impacting low altitudes).
47
Range of degree of backing and windspeed reduction at surface from geostrophic wind
Land, stable: 50 degrees, 25% speed
Land, unstable: 10-20 deg, 50% speed
Sea: 5-20 degrees, 80-90% speed
48
Turbulence severity indicators
Light - single green upside down V
Moderate - single yellow
Severe - double red
Extreme - triple red
49
Description of turbulence severity
Light - Momentary slight changes in alt/att
Moderate - Changes in alt/att but aircraft in control, airspeed varies significantly
Severe - Large abrupt changes in alt/att/airspeed
Extreme - Violent movements, impossible to control.
50
Pilot action by turbulence severity
Light - no action, minimal impact on passengers
Moderate - Pilot action required to maintain safe flight
Sev/Ext - Navigation away from area to maintain flight safety is required
51
Diurnal variation in surface wind
Heated land in day creates convection which mixes fast upper air with slower surface air, increasing windspeed at surface.
At night layers stay more separate and surface speeds reduce - wind shear may be higher.
52
Sea breeze and land breeze
In day when the land heats up (faster than sea), air above it rises and cool air from the sea is brought in.
At night this reverses.
53
Katabatic wind
Cooled air around mountains at NIGHT sinks, causing wind into valleys.
54
Anabatic flow wind
Flow of air up mountains caused by air at lower altitudes being heated up by the earth.
55
Katabatic or anabatic wind stronger?
Katabatic will be stronger as it has gravity on its side
56
Mountain waves
Strong winds perpendicular to a mountain ridge, especially if accompanied by an inversion (which restricts upwards airflow).
Downdraughts and turbulence expected on the lee side of the mountain which can exceed climbing ability of aircraft.
57
Lenticular and rotor clouds
Caused by mountain waves, lenticular clouds appear above mountain ridges and are created in a wave (lined) pattern.
Rotor clouds appear lower down around the turbulent air created on the lee side.
58
Distance over which mountain waves can create turbulence
Up to 50/100nm beyond lee side
59
Wind in the tropics
- Nature of forces
- Depiction in charts
Generally weak winds, coriolis force very low but pressure gradient isn't strong either.
Depict streamlines and isotachs on charts, with streamlines showing wind direction and isotachs showing areas of equal wind strength (not equal pressure).
60
Four main cloud groups
- Cirriform (fibrous)
- Cumuliform (heaped)
- Stratiform (layered)
- Nimbus (rain-bearing)
61
High level cloud types
High level - over 20,000ft
- Cirrus (Ci): Detached filaments, narrow bands
- Cirrocumulus (Cc): Thin layer of patchy fibrous cloud
- Cirrostratus (Cs): Transparent veil covering portion of the sky
62
Middle level cloud types
Middle level - 6k to 20k ft
- Altocumulus (Ac): Layer of patches of cloud. Coronae (coloured ring around sun/moon) are characteristic.
- Altostratus (As): Grey/bluish cloud sheet, uniform layer part covering the sky, thin enough to see sun through.
63
Low level cloud types
Low level - below 6k [S/C/N-S-C]
- Stratus (St): Grey layer with uniform base, can drizzle, sun visible through it.
- Cumulus (Cu): Detached clouds with sharp outlines, white but bases can be grey as no light reaches.
- Nimbostratus (Ns): Dark grey clouds covering the sky.
- Stratocumulus (Sc): Grey/whitish patch or sheet of cloud, can be joined or showing breaks between thicker areas.
- Cumulonimbus (Cb): Heavy dense cloud with large vertical range, dark and stormy base. Ragged Cu and Sc appear near base.
64
Meaning of cloud words:
Nimbus
Stratus
Cumulus
Cirrus
Alto
Nimbus - Rain bearing
Stratus - Layer
Cumulus - Heaped
Cirrus - High level
Alto - Medium level
65
3 other types of cloud
- Stratus/Cumulus fractus: fragments of the relevant cloud observed around the base of nimbostratus, altostratus or cumulonimbus clouds.
- Castellanus: Small turret shaped clouds that group together, indicating growth of middle layer clouds.
- Lenticularis - Lens shaped clouds formed by mountain waves.
66
Latent heat
Heat energy absorbed or given out by water during a state change.
67
Relative humidity
Vapour pressure / Saturation vapour pressure
68
Humidity Mixing Ratio (HMR)
Ratio of mass of water vapour in air parcel to the mass of dry air
69
Relative humidity and HMR at increasing altitude
As pocket of air rises the temperature decreases, so saturation vapour pressure decreases, so relative humidity increases.
However the amount of water doesn't change so HMR is constant.
(Cold air holds less water than hot air)
70
Dewpoint
The temperature at which a pocket of air will be fully saturated as temperature decreases.
71
What is the "spread"?
Difference between temperature and dew point. Low spread indicates formation of cloud or fog likely.
72
How do clouds form?
Parcel of air experiences reduction in temperature down to dewpoint
73
5 methods of cloud formation
Adiabatic
- Mass uplift of air (due to weather system or mountain range), cools as it rises
- Convection of air upwards, cooling as it rises
- Turbulence and mixing, the rising air will cool
Diabatic
- Advection - warm, moist air loses temperature to cooler land
- Radiation - air radiates out more heat than it receives
74
Rate of temperature loss as air rises
Initial below dewpoint temperature loss at DALR, about 3 deg C per 1000ft.
After dewpoint is reached, saturated air loses temp at SALR, about 1.5 deg C per 1000ft.
This is due to latent heat release as water vapour condenses into liquid state.
75
What influences the type of cloud to form?
ELR relative to DALR/SALR of the air pocket.
If ELR is greater then rising air will continue to be hotter than surrounding and form cumuliform clouds as it rises.
If ELR is around DALR/SALR it will reach a stable altitude and form stratiform clouds.
IF ELR is below DALR/SALR the rising air will cool faster than surrounding air and go back down, forming stratiform cloud or fog.
76
How do lenticular clouds form?
Air forced up by a mountain cools adiabatically as it rises, at the dewpoint water condenses and clouds form.
As the air moves back down on the leeside the water content vaporises again and clouds disappear.
So clouds only appear above the top of the mountains.
77
Orographic cloud
Cloud caused by mountains forcing wind to higher altitudes.
78
Fohn wind effect
If rising air on windward side of a mountain reaches dewpoint before the peak, clouds will form and precipitation can remove water from the air.
As it falls on the other side it will be dryer gain temperature at DALR so heat quicker.
On the leeward side therefore the wind will be warmer and cloud base higher.
79
Cloud formed by turbulence near surface
Random movements of air mean cloud is formed as some air rises and falling air revaporises. This results in stratiform clouds over a large area.
80
Cloud formed by widespread ascent
When two air masses meet (a front) the warmer air will rise above the cooler. As the warmer air rises it cools and forms cloud if it reaches dewpoint.
Will be stratiform (nimbostratus, then altostratus then cirrostratus at increasing altitude).
81
Types of precipitation from cloud types
Intermittent or continuous precipitation (starting/finishing gradually) indicates stratiform cloud. Drizzle likely from stratocumulus, rain from nimbostratus.
Rain or snow showers from cumulus or cumulonimbus.
Hail in particular from cumulonimbus.
82
Cloud cover abbreviations
SKC, FEW, SCT, BKN, OVC
SKC - sky clear
FEW - few, 1 or 2 oktas
SCT - scattered, 3 or 4 oktas
BKN - broken, 5,6 or 7 oktas
OVC - overcast, 8 oktas
83
METAR cloud summaries
Cloud cover abbreviation and flight level for the base of the clouds.
84
Impact of inversions on visibility
Inversions create a "cap" altitude which stops smoke and other contaminants rising and creates a trapped layer of poor visibility.
85
Mist vs fog
Usually mist develops into fog then back into mist.
Fog means visibility is below 1km, mist means it is further.
86
Causes of mist/fog
Cooling of air, either by a cold surface (radiation or advection fog) or two air masses (frontal fog)
87
Radiation fog formation
1) Clear skies and low wind (<7kts) cause land to radiate heat out and cool at night and a low level inversion. Some wind needed to ensure resupply of moisture from higher air, as it will be lost to dew on the ground.
2) Wind lulls to 1-2kts causing lowest air layers by cold ground to cool, air saturates and fog layer forms.
3) Radiative cooling from top of fog layer deepens the fog.
88
Radiation fog more likely in high or low pressure
High pressure (associated with calm, low wind conditions and no cloud)
89
Dispersal of radiation fog
As the land warms up in the day, the air close to it will heat and rise. The fog will lift, perhaps leading to stratus cloud.
However if the fog is thick and prevents sun from reaching the ground, the fog can last all day.
90
Does radiation fog form over land or sea?
Only over land, the sea has a more stable temperature than land.
91
Advection fog formation
Warm moist air moving over cold surface.
Can happen suddenly in day or night.
92
Sea fog
Advection fog caused by warm moist air from the sea moving over cold earth, or the opposite.
93
Frontal fog formation
2 methods
1) Cloud extending down to the surface as front passes (usually over hills, so called hill fog);
2) Air becoming saturated by evaporation of rain that has fallen.
94
Orographic fog
Formed as moist air is forced to raise over a hill.
95
Steaming fog
In very cold areas, when cool air flows over a shallow layer of warm, moist air on surface of water.
Causes a thin layer of mist above the water, but requires very cold air so only near the poles.
96
Visibility reporting
Generally reported in km (up to 9999).
Runway visual range (RVR) reported in metres if low enough (e.g. R35/0400 is 400m visibility on runway 35).
97
Divergence vs convergence
Considered at surface level - divergence is air flowing out of high pressure, convergence is air flowing into low pressure.
Above the high/low pressure point air will be drawn down/up, and the opposite effect (convergence/divergence) experienced at higher altitude.
98
Vertical movement, stability and temperature of divergent/convergent system
In divergence, air experiences subsistence -> sinking, warming and becoming more stable.
In convergence -> rising air cools and becomes unstable.
99
2 key factors in nature of an air mass
Region of origin (e.g. polar, arctic, tropical).
Track (e.g. over sea or continental)
100
Effect of origin of air mass
Maritime air will be more moist than air from continental areas.
Polar air flowing to lower latitudes gets warmed from below and becomes less stable.
Tropical air flowing to higher latitudes is cooled from below and becomes more stable.
101
Air masses towards UK
102
Front
Division between two air masses with different characteristics. Described as warm front or cold front depending on the nature of the air mass that is advancing.
103
Warm and cold fronts on charts
Warm fronts have red semi-circles in direction of movement.
Cold fronts have blue triangles in direction of movement.
104
Cold & Warm front weather diagram
105
Warm front description
- visibility, temp, wind, pressure
Warm air will slide over cool air so front is more advanced at higher altitudes than the ground level front on chart (up to 600nm ahead - RAIN 200nm ahead).
First Cirrus cloud then Cirrostratus, Altostratus, nimbostratus. May get virga from As and continuous rain/snow from Ns.
Low visibility, rising temp, veering wind, falling pressure (that stops).
106
Warm front description from air
Widespread cloud, stratus and hill fog.
Widespread precipitation.
Wind shear.
Veering wind while passing through front, will need to adjust heading.
107
Warm front diagram
108
Cold front description
- temp, wind, pressure
Cold air doesn't "slide" under warm air as much so steeper front covering less distance.
Warm air displaced upwards is unstable so cumulonimbus cloud likely in front, cumulus cloud behind the front.
Drop in temperature, heavy showers, thunderstorms. Wind veers, pressure falls then rises once front passes.
109
Cold front description from air
Cumulonimbus clouds can cause thunderstorms and violent winds.
Icing could be a problem, windshear, heavy showers.
Polar air behind the cold front may be clear, but the front should be avoided.
110
Cold front diagram
111
Warm sector
Area between warm and cold fronts in the UK associated with stable SW winds and tropical maritime air.
Low stratus clouds, windshear and mountain wave activity.
112
Polar Front Depression direction
Parallel to warm sector isobars
113
Stationary front
Boundary between warm and front areas of air which isn't moving
114
Frontal Wave
Warm air tends to bulge into cold air, creating a wave (frontal wave). The leading edge of the wave is a warm front, following edge is a cold front.
Cold front usually moves faster than warm front.
115
Frontal depression
The pressure at the tip of a frontal wave falls sharply, so a depression forms.
116
Occluded front
- depiction on charts
In a frontal wave, when the cold front (travelling faster) catches up with the warm front, an occluded front (or occlusion) occurs.
Depicted as alternated red semi-circle and blue triangle marks.
117
2 types of occluded front
Cold front occlusion is when the following cold front remains at the surface.
Warm front occlusion when the warm front remains at the surface.
118
Description of occluded front
Clouds dependent on the individual air masses, but cumulonimbus over the occluded front and stratus (Cs, As) over the warm front are likely.
Brief thunderstorms as unstable air is forced upwards at the front itself.
119
Norwegian front theory
This is the basic theory we follow in PPL, but it is a simplification and we need to review actual forecasts in detail to understand weather.
120
Depression
- description
- conditions
This is a low pressure air system. Convergence and rising air in the centre of the system.
Rising cooling air leads to cumuliform clouds, showers, although visibility may be good if no rain as particles carried away vertically.
121
Trough
A V-shaped extension of isobars in a low pressure system.
Increases low level convergence and strong convection, creating hazardous weather and Cumulonimbus clouds.
122
Cyclone
[Or tropical revolving storm, hurricane, typhoon]
Intense depression around 10-20 degrees latitude. Small (200-300nm) with small centre (10nm) but very low pressure and high winds (100kph).
123
Anticyclone or "high"
An are of high pressure at the surface, clockwise winds (NH) with divergence at surface and convergence at height.
Caused by greater convergence at upper layers than the divergence at the surface.
124
Description of a high (anticyclone)
Can cause an inversion if subsiding air heats to higher temp than the lower layers => stratus, smoke trapped at lower levels, gloomy winter days.
If the sky is clear radiation from earth can lead to fog.
125
Ridge of high pressure
Similar experience to high pressure system
126
Col
Areas of constant pressure in-between 2 high and 2 low pressure systems.
Generally light winds, fog in winter, high temperatures and showers/thunderstorms in summer.
127
Three triggers for thunderstorm
i) Deep instability, so rising air keeps rising
ii) High moisture content
iii) Trigger action:
e.g. Front or mountain forcing air upwards, strong heating from earth, heating of polar air or convergence
128
Stages of thunderstorm
i) Cumulus stage
ii) Mature stage
iii) Dissipating stage
129
Cumulus stage of thunderstorm description
Moist air cools as it rises, with water vapor condensing when it reaches dewpoint. Latent heat given off reduces cooling rate, so clouds are warmer and rise faster than surroundings. Air at all levels drawn in from surrounding air leading to significant vertical gains up to troposphere, where water will freeze or be super-cooled (CLOUD BECOMES GLACIATED)
Strong, warm updraughts.
130
Mature stage of thunderstorm description
The updraughts are not strong enough to hold cold water up so they fall, taking air with them, creating very cold downdraughts. The cold downdraughts and warm updraughts create hazardous windshear.
Heavy rain is now falling and downdraughts out of the bottom of the cloud are dangerous.
Anvil shape of the now cumulonimbus cloud is visible at top.
131
Dissipation stage of thunderstorm description
Cold downdraughts cause warm updraughts to weaken, reducing supply of moist air to the top.
Cloud collapses, possibly into stratiform.
132
Distance to leave from thunderstorms
At least 10nm, 20nm from larger ones
133
Gust front
Wind at surface caused by cold downdraughts out of the bottom of thunderstorms, due to the cold precipitation and cold downdraughts.
134
Microburst
- What is it?
- 2 types
2nm downdraft, 5-15 mins
Wet microbursts have significant rain, dry microbursts have no visible signs.
135
Clear ice
Caused by supercooled water (0 to -20 deg C). Initial large drops freeze on contact with metal surface. Released latent heat slows freezing of further drops so they spread over the surface before freezing.
Result is a clear sheet of ice over a surface, affecting aerodynamics and weight.
136
Rime ice
Forms when supercooled small water drops freeze instantly on a below zero surface. Will be lumpy, often forms on leading edges.
137
Cloudy/mixed ice
Mix of clear and rime ice
138
Hoar frost
Formed when moist air comes into contact with a sub-zero surface.
Can happen to a plane parked overnight, or travelling from a cold air pocket into a warmer, moist air pocket.
Not super dangerous, but can affect visability.
139
Icing and air temperature
Highest risk between 0 and -20 deg C.
From -20 deg C to -40 deg C it moderates a little.
Below -40 deg C (e.g. cirrus cloud at high alt) the risk is low.
Descending to warmer air, or perhaps rising to cooler air can be preferable.
140
Icing in cloud/condition types
Cumulus cloud has high risk at temp down to -20 deg C. Vertical air movement can mean temperatures varying so take care.
Stratiform cloud water drops down to -15 deg C therefore high risk of icing.
Raindrops and drizzle are a high risk if OAT is below zero, e.g. in the cooler air ahead of (and under) warm front.
141
Max temperature at which carb icing can form
30 deg C
142
Radiosonde
Instrumentation carried up into higher altitudes by a weather balloon.
Can also have dropsondes which are dropped from a plane.
143
SIGMET
Special weather report to indicate significant meteorological conditions (e.g. thunderstorms, tropical revolving storms, severe squall etc.)
144
Three formats of weather report
i) Internet services
ii) GAMET - text based, fax or phone
iii) Graphic charts and data via METFAX
145
CB amount abbreviations
ISOL - isolated, individual clouds
OCNL - occasional, well separated clouds
FRQ - frequent, little or no separation
EMBD - embedded, contained in layers of other clouds
146
CAVOK
Visibility > 10km
No cloud below 5,000ft aal (or highest minimum sector altitude if lower)
No significant weather near aerodrome
147
Warning regarding CAVOK
Updates when weather changes only require an update if cloud appears below 1,500 ft, so CAVOK only really guarantees no cloud below 1,500 ft.
148
TEMPO
- Meaning
- How it is written
Temporary variation lasting less than 60 minutes, or less than half of the TREND period.
e.g. passing thunderstorm
Will be followed by 4 digit code indicating starting hour and ending hour (next 4 digit code is visibility).
e.g. TEMPO 2023 5000 means visibility 5km between 2000 and 2300
149
BECMG
- Meaning
- How it is written
At end of the stated period the stated weather will become the steady state.
DDTT/DDTT format for start and end period for the state.
e.g. BECMG 1910/1912 9999 means on 19th between 1000 and 1200 visibility going to over 10km
150
Written code for cloud cover
Initial code for coverage (SKC, FEW, SCT, BRK, OVC) then FL of cloud base.
e.g. BKN008 is broken cloud above 800ft
151
Initial code for TAF report
TAF then [aerodrome code]
DDHHMMZ for time of report
DDHH/DDHH for start/end of time period
Then description of weather
e.g. TAF EGDL 190600Z 1907/1916 means report sent on 19th at 0600, covering 0700 to 1600 on 19th.
152
TAF cloud base height basis
Cloud base in height above aerodrome, not altitude
153
GAMET
- Stands for
- Description
General Aviation Meteorological Forecast
Plain text forecast for low level general aviation users in UK
- GAMET South West
- GAMET South East
- GAMET Central
- GAMET North
154
Special forecast
Where insufficient weather information is available for a given aerodrome, can request a special forecast for your flight.
Need 2 hours notice (4 hours for over 500nm).
They only cover the areas outside standard UK area forecasts.
155
TAF
- Stands For
- Description
- Validity, frequency
Terminal Aerodrome Forecast
Text messages in ICAO format for aeoodromes where observations are taken.
Usually cover 9 to 24 hours.
9 hour TAFs updated every 3 hours, 12-24 hours updated every 6 hours.
156
Abbreviations:
- BR
- +/-
- IR
- GR
- GS
- HPA
BR: Mist
+/-: Heavy/light
IR: Ice on runway
GR: Hail (>5mm)
GS: Small hail
HPA: Hectopascals
157
Abbreviations:
- MiFG
- VV
- BCFG
- TS
- CB
- NSW
MiFG: Shallow fog
VV: Vertical visibility (i.e. cloud base) not measured, sky is obscured
BCFG: Fog patches
TS: Thunderstorm
CB: Cumulonimbus
NSW: No significant weather
158
Abbreviations:
- LAN
- COT
- SEA
- VC
- AIREP
LAN: Over land
COT: Coast
SEA: At sea
VC: Vicinity
AIREP: Aircraft Report
159
METAR
Meteorological aerodrome observation reports taken at 30 min to 1 hour intervals.
Only have DDHHMM time code, no validity period.
Two temperatures reported - air temp and dewpoint (e.g. 09/07) at 1.2m height.
QNH also included.
160
TREND forecast
AKA Landing forecast
TREND prediction for weather for 2 hours after a METAR observation
161
VHF meteorological information in flight
- FIS or ATC can provide information;
- VOLMET radio broadcast updated every hour and half past;
- ATIS.
Note FIS/ATC will automatically provide any SIGMET info
162
VOLMET items
Current observed conditions (at aerodrome)
Landing forecast
SIGMET (if any)
Forecast trend for 2 hours
163
Altitude limit of spot wind chart
24,000 ft
164
Where does tropical maritime air in UK originate from?
Azores
165
QFF
Pressure measured at ground station, reduced to MSL based on atmospheric conditions [then used to calculate QFE and QNH]
166
Summer high pressure conditions
Large isobar spacing, calm winds, formation of local wind systems, few high cumulus clouds
167
Winter high pressure conditions
Light winds, widespread fog
168
Wind speed symbols
169
European named winds
170
Description of Mistral wind
Speeds up due to passage through mountain valleys.
171
Description of Bora wind
From NE into adriatic, down mountains
172
Snow showers
173
Thunderstorm
174
Main requirement for rain
Moderate to strong updraughts
175
Year round high pressure systems
At 30 degrees N/S, oceanic latitudes.
Hot equatorial air cooling as it descends further N/S.
176
Result of cold air flowing in at top of troposhere
Low pressure at high point (as if low pressure were drawing the cold air in), flowing down to ground and divergence at surface.
Showers and thunderstorms can develop.
177
Cloud ceiling
Height above aerodrome of lowest layer of cloud below 20k ft covering half of the sky
