Ch 6 Quiz: Clouds & Fog — Classification & Visibility

Clouds form when the air temperature falls to the dew point temperature (100% relative humidity), causing water vapour to condense onto condensation nuclei forming cloud droplets.

Freezing point

Correct Incorrect Correct answer

Dew point

Correct Incorrect Correct answer

Absolute zero

Correct Incorrect Correct answer

Critical temperature

Correct Incorrect Correct answer

The base of convective (cumuliform) clouds is at the Lifting Condensation Level (LCL), where a rising parcel cools to its dew point. This can be estimated: (T – Td) ÷ 2.5 × 1000 ft (using °C).

The lifting condensation level (LCL)

Correct Incorrect Correct answer

The tropopause

Correct Incorrect Correct answer

The 0°C isotherm

Correct Incorrect Correct answer

The inversion height

Correct Incorrect Correct answer

ICAO/WMO definition: FOG = visibility < 1000 m with water droplets near the surface. MIST = visibility 1000–5000 m (relative humidity ≥ 95%). Haze = visibility <5000 m due to dry particles.

5000 m

Correct Incorrect Correct answer

1000 m

Correct Incorrect Correct answer

200 m

Correct Incorrect Correct answer

500 m

Correct Incorrect Correct answer

Radiation fog: forms on clear calm nights over land when the surface cools by radiation, cooling the air above to dew point. Conditions: clear sky (no cloud blanket), light winds (2–8 kt to mix moisture but not disperse), high moisture content.

Over oceans in winter

Correct Incorrect Correct answer

On clear, calm nights over land when the surface radiates heat

Correct Incorrect Correct answer

During the day in summer

Correct Incorrect Correct answer

In strong winds

Correct Incorrect Correct answer

Advection fog: warm moist air moves over a cold surface (land or sea) and is cooled from below. Common over cold ocean currents (Grand Banks, California Current). Unlike radiation fog, it can persist in moderate winds.

Cold air moves over warm water

Correct Incorrect Correct answer

Warm moist air moves over a cold surface

Correct Incorrect Correct answer

Radiation cools the ground

Correct Incorrect Correct answer

Air descends from mountains

Correct Incorrect Correct answer

Hill fog (orographic fog/cloud) = stratus or low cloud that envelops hills and mountains when moist air is forced to ascend. The cloud base is AT or BELOW the hilltop. Particularly hazardous for VFR flight in hilly terrain.

A type of radiation fog on hills

Correct Incorrect Correct answer

Orographic cloud — stratus that forms as moist air is forced upslope and cools to dew point

Correct Incorrect Correct answer

Sea fog on hilltops

Correct Incorrect Correct answer

Smoke-induced fog

Correct Incorrect Correct answer

Steam fog/Arctic sea smoke: cold dry air flows over warmer open water. Water evaporates rapidly, immediately condenses in the cold air → wispy columns of fog. Common over unfrozen Arctic/Antarctic seas in winter.

Warm moist air flows over cold water

Correct Incorrect Correct answer

Very cold air flows over relatively warm open water — evaporation and immediate condensation

Correct Incorrect Correct answer

Sea breeze meets land air

Correct Incorrect Correct answer

Ice melts rapidly

Correct Incorrect Correct answer

Cumulonimbus clouds produce the most severe aviation hazards: extreme turbulence, heavy precipitation, hail, lightning, icing, microbursts, and windshear. ICAO requires that Cb clouds be avoided.

Cirrus

Correct Incorrect Correct answer

Cumulonimbus (Cb)

Correct Incorrect Correct answer

Altostratus

Correct Incorrect Correct answer

Cirrostratus

Correct Incorrect Correct answer

Altocumulus lenticularis (lenticular clouds) are lens-shaped stationary clouds that form at wave crests in mountain wave/lee wave systems. Their presence indicates significant wave activity and possible severe turbulence in the rotor zone below.

Radiation fog conditions

Correct Incorrect Correct answer

Mountain wave activity with potentially severe turbulence below

Correct Incorrect Correct answer

Approaching warm front

Correct Incorrect Correct answer

Sea breeze cloud

Correct Incorrect Correct answer

Cumulonimbus incus: the anvil-topped Cb where the cloud top has spread horizontally at the tropopause. The anvil points downwind. Incus = Latin for anvil. Indicates a mature, highly developed, extremely dangerous storm.

Cb with a wall cloud

Correct Incorrect Correct answer

Cb with an anvil top — indicating cloud has reached the tropopause

Correct Incorrect Correct answer

Cb with mammatus

Correct Incorrect Correct answer

Isolated Cb

Correct Incorrect Correct answer

High cloud family (above 20,000 ft / 6,000 m): Cirrus (Ci), Cirrocumulus (Cc), Cirrostratus (Cs). These are composed primarily of ice crystals. Cumulonimbus, though it tops very high, bases are in the low cloud range.

Altostratus

Correct Incorrect Correct answer

Cirrus (5,000–13,700 m / 16,500–45,000 ft)

Correct Incorrect Correct answer

Cumulonimbus

Correct Incorrect Correct answer

Nimbostratus

Correct Incorrect Correct answer

Virga: precipitation (rain or snow) that evaporates or sublimes in dry air before reaching the ground. It appears as trailing streaks below a cloud. Virga can produce strong evaporative cooling, downdrafts, and windshear beneath it.

Rain reaching the surface

Correct Incorrect Correct answer

Precipitation that evaporates before reaching the ground

Correct Incorrect Correct answer

A cloud formation indicating tornado

Correct Incorrect Correct answer

Fog over the ocean

Correct Incorrect Correct answer

Mammatus (mamma): pouch-like protrusions hanging from the underside of Cumulonimbus anvils. They indicate strong downdrafts and are associated with severe thunderstorms. Their presence signals particularly hazardous conditions nearby.

Stratus layers

Correct Incorrect Correct answer

Severe thunderstorms (Cumulonimbus) — indicate strong downdrafts

Correct Incorrect Correct answer

Sea fog

Correct Incorrect Correct answer

Cirrus clouds

Correct Incorrect Correct answer

Freezing fog: fog where temperature is at or below 0°C. The droplets are supercooled liquid water. They freeze on contact with aircraft surfaces (and roads, vegetation) causing clear ice. Reported as FZFG in METAR.

Fog forms at temperatures above 0°C

Correct Incorrect Correct answer

Fog exists at temperatures below 0°C — supercooled droplets freeze on contact with sub-zero surfaces

Correct Incorrect Correct answer

All fog freezes at night

Correct Incorrect Correct answer

Fog in the stratosphere

Correct Incorrect Correct answer

WMO (2017 Atlas) recognises 10 cloud genera: Ci, Cc, Cs, Ac, As, Ns, Sc, St, Cu, Cb. These are grouped into three altitude levels (high, middle, low) plus vertically developed (Cu, Cb, Ns can span levels).

7

Correct Incorrect Correct answer

10

Correct Incorrect Correct answer

12

Correct Incorrect Correct answer

14

Correct Incorrect Correct answer

Nimbostratus (Ns): dark grey layer cloud associated with continuous, persistent rain or snow. Bases are typically very low and ragged. Associated with warm fronts. Significant icing hazard within and below cloud.

Brief showers

Correct Incorrect Correct answer

Continuous rain or snow, obscuring cloud base, often bringing icing

Correct Incorrect Correct answer

Thunder and lightning

Correct Incorrect Correct answer

No precipitation

Correct Incorrect Correct answer

LCL (ft) ≈ (T − Td) / 2.5 × 1,000. Example: T = 25°C, Td = 15°C → (25-15)/2.5 × 1000 = 4,000 ft. This gives approximate Cu base height for surface-based convection.

Multiplying humidity by 100

Correct Incorrect Correct answer

(T − Td) ÷ 2.5 × 1000 ft (where T and Td are in °C at the surface)

Correct Incorrect Correct answer

Adding temperature and dew point

Correct Incorrect Correct answer

Dividing pressure by 100

Correct Incorrect Correct answer

Stratus: featureless low grey layer cloud. Mechanisms: (1) radiation fog lifting slightly in morning breeze, (2) turbulent mixing of moist stable air, (3) advection of moist air at low level. Rarely produces more than light drizzle.

Intense convection

Correct Incorrect Correct answer

Turbulent mixing of moist air in a stable, shallow layer — or by radiation cooling of the top of a fog layer

Correct Incorrect Correct answer

Frontal lifting

Correct Incorrect Correct answer

Orographic descent

Correct Incorrect Correct answer

Frontal (precipitation) fog: warm rain falls from above the front into cooler sub-frontal air, evaporates, and raises the humidity of the cold air to saturation, forming fog. Common ahead of warm fronts, especially in winter.

Fog caused by rain condensing

Correct Incorrect Correct answer

Fog that forms when rain falls through a dry, cooler air mass below a warm front, saturating the sub-frontal air

Correct Incorrect Correct answer

Fog in precipitation areas only

Correct Incorrect Correct answer

Same as radiation fog

Correct Incorrect Correct answer

LVPs (Low Visibility Procedures) are activated at most major airports when RVR falls below 600 m (for Cat II/III approaches). They impose minimum separations and taxiway controls. Some airports use 800 m as the LVP trigger.

800 m

Correct Incorrect Correct answer

600 m

Correct Incorrect Correct answer

1000 m

Correct Incorrect Correct answer

400 m

Correct Incorrect Correct answer

Cumulus humilis (Cu hum): shallow, flat-based cumulus with limited vertical development. Indicates daytime heating and mild instability — generally benign. Their tops are suppressed by a subsidence inversion. No significant aviation hazard.

Approaching storm

Correct Incorrect Correct answer

Slight convective activity only — unstable boundary layer with limited vertical extent

Correct Incorrect Correct answer

Sea fog beginning

Correct Incorrect Correct answer

Mountain wave cloud

Correct Incorrect Correct answer

Ac castellanus: turreted/castellated altocumulus with vertical development. Indicates mid-level instability and is a classic early morning indicator of afternoon thunderstorm potential. Its presence in the morning warrants thunderstorm vigilance.

Stable upper air

Correct Incorrect Correct answer

Mid-level instability — precursor to afternoon thunderstorm development

Correct Incorrect Correct answer

Sea breeze front

Correct Incorrect Correct answer

Frontal passage

Correct Incorrect Correct answer

METAR cloud amounts: SKC=0, FEW=1-2 oktas, SCT=3-4 oktas, BKN=5-7 oktas, OVC=8 oktas. FEW/SCT/BKN/OVC + height in hundreds of feet. E.g. BKN030 = broken cloud at 3,000 ft.

0 oktas

Correct Incorrect Correct answer

1–2 oktas

Correct Incorrect Correct answer

3–4 oktas

Correct Incorrect Correct answer

5–7 oktas

Correct Incorrect Correct answer

Contrails form when hot humid jet exhaust mixes with cold ambient air (typically above ~26,000 ft / −40°C), causing water vapour to condense and freeze. Persistent contrails indicate ice-supersaturated air. Can evolve into cirrus sheets.

Temperature is above 0°C

Correct Incorrect Correct answer

Exhaust water vapour condenses and freezes in the cold, supersaturated upper troposphere/lower stratosphere

Correct Incorrect Correct answer

Aircraft is burning fuel inefficiently

Correct Incorrect Correct answer

High humidity only at low altitude

Correct Incorrect Correct answer

Radiation fog disperses as: solar heating raises surface temperature above dew point, or moderate winds mix foggy air with drier air aloft. Thick fog may persist all day if cloud cover prevents solar heating.

Calm clear nights

Correct Incorrect Correct answer

Increasing wind (turbulent mixing with drier air above), heating of the surface by sun (raising temperature above dew point)

Correct Incorrect Correct answer

More humidity

Correct Incorrect Correct answer

Falling pressure

Correct Incorrect Correct answer

Dew point temperature: the temperature to which a parcel of air must be cooled (at constant pressure and moisture content) for saturation (RH=100%) to occur. Condensation (dew, fog, cloud) begins at this temperature.

Water freezes

Correct Incorrect Correct answer

Air becomes saturated — if air is cooled to this temperature at constant pressure and moisture content, condensation begins

Correct Incorrect Correct answer

Humidity is 50%

Correct Incorrect Correct answer

Clouds reach their maximum height

Correct Incorrect Correct answer

Dense fog over the Indo-Gangetic Plain (Delhi, Amritsar, Varanasi) is worst in winter due to: (1) long clear nights → strong radiation cooling, (2) high moisture content from monsoon residue, (3) light winds, (4) stable inversions trapping fog.

Monsoon (June–September)

Correct Incorrect Correct answer

Winter (November–February) — especially in the Indo-Gangetic Plain, where radiation fog is severe and persistent

Correct Incorrect Correct answer

Summer (April–May)

Correct Incorrect Correct answer

Post-monsoon (October)

Correct Incorrect Correct answer

FZFG: Freezing Fog — FZ (freezing) + FG (fog). Temperature ≤ 0°C, visibility < 1000 m. Supercooled liquid fog droplets freeze instantly on contact with aircraft surfaces, equipment, and roads. Reported when T ≤ 0°C and FG conditions exist.

Freezing rain fog

Correct Incorrect Correct answer

Freezing fog — fog where temperature is at or below 0°C and supercooled droplets freeze on contact

Correct Incorrect Correct answer

Light fog

Correct Incorrect Correct answer

Fog visibility 200 m

Correct Incorrect Correct answer

MI = shallow (from French: mince). MIFG = shallow fog — patches or layer of fog that does not cover the entire aerodrome or is shallow (< 2 m). BCFG = patches of fog. PRFG = partial fog. Each has different reporting and operational significance.

Moderate intensity fog

Correct Incorrect Correct answer

Shallow fog — MI (shallow) + FG, meaning fog that does not cover the area completely or is very shallow

Correct Incorrect Correct answer

Mist only

Correct Incorrect Correct answer

Moderate ice fog

Correct Incorrect Correct answer

Stratus (St): low cloud family, base typically 0–2,000 ft AGL. Grey, uniform sheet. Produces: drizzle, mist, hill fog. Ceiling can be at ground level (fog). Particularly problematic in coastal areas and post-frontal moist airstreams.

Above 10,000 ft

Correct Incorrect Correct answer

Below 2,000 ft AGL — usually 100–1,000 ft in overcast grey layers

Correct Incorrect Correct answer

At the freezing level

Correct Incorrect Correct answer

Between 6,500–23,000 ft

Correct Incorrect Correct answer

Cu congestus: towering cumulus with cauliflower tops, base at LCL, glaciation not yet occurring. Can produce heavy showers and turbulence. If the updraft continues and glaciation occurs at the top, it becomes a Cumulonimbus.

Flat base only

Correct Incorrect Correct answer

Towering vertical development (taller than wide) but no glaciation — precursor to Cumulonimbus development

Correct Incorrect Correct answer

Very low base

Correct Incorrect Correct answer

Anvil top

Correct Incorrect Correct answer

Cb calvus: the cloud top has become glaciated (smooth, fibrous ice crystal appearance) indicating freezing has occurred, but the anvil has not yet spread. Intermediate stage between Cu congestus and Cb incus.

Cb with an anvil

Correct Incorrect Correct answer

Cb whose top has a rounded, smooth, fibrous (glaciated) appearance but without a well-developed anvil — an early stage of Cb development

Correct Incorrect Correct answer

A tropical Cb only

Correct Incorrect Correct answer

Cb with wall cloud

Correct Incorrect Correct answer

Cirrus (Ci): composed of ice crystals at high altitude (>6,000 m). Forms delicate, wispy white filaments. Does not produce significant precipitation at the surface. Indicates upper-level moisture and jet streams. Precedes warm fronts by 12–24 hours.

Stratus

Correct Incorrect Correct answer

Cirrus — at the high altitude where Ci forms (>20,000 ft), temperatures are below −40°C and only ice crystals exist

Correct Incorrect Correct answer

Altocumulus

Correct Incorrect Correct answer

Cumulonimbus base

Correct Incorrect Correct answer

Altostratus: middle-level grey/blue sheet cloud (6,500–23,000 ft). Typically precedes a warm front, thickening and lowering as the front approaches. Eventually becomes Nimbostratus. ‘Watery sun’ effect = thin As. Thick As → continuous rain below.

Convective instability

Correct Incorrect Correct answer

Approaching warm front or upper-level trough — thin As can be seen through (the sun appears watery), thick As obscures the sun

Correct Incorrect Correct answer

Radiation fog conditions

Correct Incorrect Correct answer

Cold, dry air mass

Correct Incorrect Correct answer

ICAO cloud étages: LOW (surface–6,500 ft), MIDDLE (6,500–23,000 ft), HIGH (16,500–45,000 ft). Vertically developed (Cu, Cb) span multiple levels. The étage system helps classify and communicate cloud cover effectively.

0–2,000 ft

Correct Incorrect Correct answer

6,500–23,000 ft (2,000–7,000 m)

Correct Incorrect Correct answer

Above 20,000 ft

Correct Incorrect Correct answer

At the freezing level only

Correct Incorrect Correct answer

Ceilometer: LIDAR-based (laser) instrument measuring cloud base height. Sends upward laser pulses and measures time-of-flight of backscattered signal from cloud base. Automatically provides cloud base, cloud layer heights, and vertical visibility data for METAR generation.

Temperature

Correct Incorrect Correct answer

Cloud base height using a pulsed laser beam (LIDAR principle) — measures backscatter from cloud base

Correct Incorrect Correct answer

Wind speed

Correct Incorrect Correct answer

Visibility

Correct Incorrect Correct answer

Undulatus (Ac/Sc undulatus): parallel bands/rolls of cloud formed by wave motion (Kelvin-Helmholtz waves) at a stable layer interface. Can indicate windshear at that level. Generally low turbulence unless Kelvin-Helmholtz instability is strong (breaking waves = moderate turbulence).

Random cloud patches

Correct Incorrect Correct answer

Parallel bands or ripples in the sky — formed by wave motion in a stable atmospheric layer

Correct Incorrect Correct answer

A solid grey sheet

Correct Incorrect Correct answer

A single lenticular cloud

Correct Incorrect Correct answer

Optimal radiation fog wind: 2–8 kt. Calm = cooling confined to a very thin layer (dew/frost rather than deep fog). Stronger wind (>10–12 kt) mixes dry air from above, dispersing or preventing fog. 2–8 kt is the sweet spot for widespread fog development.

Calm (0 kt) or very strong (>20 kt)

Correct Incorrect Correct answer

2–8 kt — light wind mixes moisture and cooling through a shallow layer without dispersing it

Correct Incorrect Correct answer

15–20 kt

Correct Incorrect Correct answer

Above 25 kt

Correct Incorrect Correct answer

Altocumulus: middle-level cloud (6,500–23,000 ft), composed of water droplets (can be ice at colder temperatures). Appears as white/grey rounded masses, sheets, or patches. Often in rolls or waves. Can indicate turbulence if highly variable or castellated.

Ice crystals only

Correct Incorrect Correct answer

Mainly water droplets (and some ice at lower temperatures), forming in the middle étage — white and grey patches or sheets

Correct Incorrect Correct answer

Predominantly snow pellets

Correct Incorrect Correct answer

Volcanic ash

Correct Incorrect Correct answer

SIGMETs for CB: issued for isolated thunderstorms associated with hail or squall lines, widespread embedded Cb, or Cb tops above FL250 (for high-level SIGWX). The criterion varies by region and weather service; ICAO Annex 3 sets the framework.

Any single CB

Correct Incorrect Correct answer

Isolated Cb with tops above FL100 in IMC, or areas of widespread/embedded Cb above FL250

Correct Incorrect Correct answer

Only squall lines

Correct Incorrect Correct answer

Cb in the tropics only

Correct Incorrect Correct answer

Classic warm front cloud sequence (Norwegian Model): Cirrus (Ci) 500–700 km ahead → Cirrostratus (Cs, halo) 400–500 km → Altostratus (As) 300 km → Nimbostratus (Ns) + rain 200 km → Stratus (St) near surface front → clearance in warm sector.

Cb → Ns → Ac → Ci

Correct Incorrect Correct answer

Ci → Cs → As → Ns → St/Sc → clearance

Correct Incorrect Correct answer

St → Ns → As → Ci

Correct Incorrect Correct answer

No cloud sequence

Correct Incorrect Correct answer

Diurnal convective maximum: solar heating peaks around local noon–early afternoon. Maximum surface temperatures → maximum buoyancy of rising parcels → maximum CAPE → tallest Cb → maximum thunderstorm activity. Typical peak: 14:00–18:00 local time.

Pressure is lowest in the afternoon

Correct Incorrect Correct answer

Solar heating is maximum, driving strongest surface-based convection — maximum CAPE and maximum LCL heating occur in mid-afternoon

Correct Incorrect Correct answer

Wind is strongest at noon

Correct Incorrect Correct answer

Coriolis is weakest at midday

Correct Incorrect Correct answer

PIBAL: pilot balloon tracked visually or by radar to measure upper wind. Operator tracks azimuth and elevation at timed intervals → calculates wind at each level. Used at remote/developing-world stations. Largely replaced by radiosonde and ACARS at major stations.

Temperature

Correct Incorrect Correct answer

Upper wind by tracking the balloon's position with a theodolite — obsolete but still used at some stations

Correct Incorrect Correct answer

Humidity only

Correct Incorrect Correct answer

Cloud top height

Correct Incorrect Correct answer

Haze: visibility reduction by dry particles (dust, salt, pollution) — RH typically <95%. Smoke: combustion products. Neither requires saturation (unlike fog/mist). METAR codes: HZ (haze), FU (smoke), DU (dust), SA (sand). Differ from FG (RH=100%).

They are not meteorological

Correct Incorrect Correct answer

Smoke/haze consist of dry particles (no liquid droplets) — visibility reduced but RH may be well below 100%

Correct Incorrect Correct answer

They form only in cities

Correct Incorrect Correct answer

Fog is denser

Correct Incorrect Correct answer

Ceiling: height above ground of the lowest layer of cloud reported as BKN (5–7 oktas) or OVC (8 oktas) or obscuration. Used to determine IFR/MVFR/VFR conditions. Example: ceiling 300 ft = BKN030 in METAR → well below VFR minima.

The maximum altitude of the aircraft

Correct Incorrect Correct answer

The height of the lowest broken (BKN) or overcast (OVC) cloud layer, or obscuration — used for IFR/VFR categorisation

Correct Incorrect Correct answer

The cloud top

Correct Incorrect Correct answer

Any cloud in the sky

Correct Incorrect Correct answer

VV (vertical visibility): used when the sky is obscured by a surface-based phenomenon (dense fog, heavy snow, dust storm). The number after VV is the vertical visibility into the phenomenon (e.g. VV002 = vertical visibility 200 ft). Ceiling = 0 effectively.

Overcast cloud at the stated height

Correct Incorrect Correct answer

Vertical visibility into an obscuring phenomenon (fog, heavy snow, dust) — the base of the obscuration is at the surface

Correct Incorrect Correct answer

No cloud visible

Correct Incorrect Correct answer

Cloud above 5,000 ft

Correct Incorrect Correct answer

Altostratus: middle-level (6,500–23,000 ft), can show ‘watery sun’, may produce light precipitation that evaporates before reaching ground. Nimbostratus: thick dark layer (base typically below 6,500 ft), continuous rain or snow reaches ground. As → Ns as front approaches.

Altitude only

Correct Incorrect Correct answer

As may be thin enough to show a watery sun; Ns is thick, dark, produces continuous rain, and base is much lower — often ragged

Correct Incorrect Correct answer

No difference

Correct Incorrect Correct answer

Ns is a high cloud

Correct Incorrect Correct answer

Warm advection fog in India: during pre-monsoon (April–May), warm moist southerly air from the Bay of Bengal advances over the Deccan plateau. If the air cools below dew point over land, advection fog forms, particularly overnight into the morning.

Radiation fog

Correct Incorrect Correct answer

Advection fog — moist air advecting inland from the Bay of Bengal meets warm land surfaces

Correct Incorrect Correct answer

Steam fog

Correct Incorrect Correct answer

Frontal fog

Correct Incorrect Correct answer

A 200 ft ceiling requires at minimum CAT II operations (DH 100 ft, RVR ≥300 m). If the aircraft, crew, and airport are not CAT II certified, no approach is permitted. CFIT risk is extreme at such low ceilings without precise ILS guidance.

Turbulence only

Correct Incorrect Correct answer

CFIT (Controlled Flight Into Terrain) risk on approach; CAT II/III ILS required; most operations require CAT II/III minima (decision height 100 ft)

Correct Incorrect Correct answer

Icing only

Correct Incorrect Correct answer

No risk in a modern aircraft

Correct Incorrect Correct answer

OPMET: the set of operational meteorological products for aviation defined by ICAO Annex 3 and distributed through the ICAO OPMET Global Center (OGC). Includes: METAR, SPECI, TAF, SIGMET, AIRMET, PIREP, WINTEM, SIGWX, WAFS products.

Only METAR

Correct Incorrect Correct answer

METAR, TAF, SIGMET, AIRMET, PIREP, VOLMET — all aviation operational weather products distributed via WMO GTS and ICAO OPMET networks

Correct Incorrect Correct answer

Forecasts only

Correct Incorrect Correct answer

NWP model output only

Correct Incorrect Correct answer

Nimbostratus (Ns): dark grey to charcoal, often appearing almost black from below. The darkness is due to the extreme thickness of the cloud (several km) which absorbs most solar radiation. Its ragged base (pannus/scud) is a characteristic feature.

Bright white

Correct Incorrect Correct answer

Dark grey to nearly black — the thick cloud absorbs most solar radiation, making it appear very dark from below

Correct Incorrect Correct answer

Blue

Correct Incorrect Correct answer

Reddish

Correct Incorrect Correct answer

Pannus (formerly fractus): ragged accessory cloud beneath Nimbostratus or Cb. Forms when rain evaporates below the cloud base, increasing humidity, and turbulent mixing creates wispy detached cloud fragments. Indicates active precipitation from above.

A type of Cumulonimbus

Correct Incorrect Correct answer

Ragged, wispy cloud fragments below the main Ns or Cb base — formed by turbulence and evaporation near the base

Correct Incorrect Correct answer

The cloud ceiling

Correct Incorrect Correct answer

A lenticular cloud variant

Correct Incorrect Correct answer

LCL (ft) ≈ (T − Td) / 2.5 × 1,000. Example: T=30°C, Td=20°C → (30−20)/2.5 × 1,000 = 4,000 ft cloud base. Valid for surface-based convection in the NH.

Cloud top height

Correct Incorrect Correct answer

Height of the cloud base above the surface for surface-based convective clouds

Correct Incorrect Correct answer

Temperature at cloud base

Correct Incorrect Correct answer

Freezing level

Correct Incorrect Correct answer

Cirrostratus halos: ice crystals (typically hexagonal plates) act as prisms, refracting light at specific angles. The common 22° halo is formed by 60° prism columns; the 46° halo by 90° faces. Halos are a reliable indicator of Cs and approaching warm front.

It contains water droplets that scatter light

Correct Incorrect Correct answer

Ice crystals in Cs refract and reflect light at 22° and 46° angles — producing halos around the sun or moon

Correct Incorrect Correct answer

It is very thin

Correct Incorrect Correct answer

It blocks all light

Correct Incorrect Correct answer

TCU in METAR: cloud reported as ‘FEW030TCU’ or ‘BKN025TCU’. Indicates Cu with significant vertical extent (towering) — potential severe turbulence, icing, and imminent Cb development. TCU warrants pilot caution even if not yet full Cb.

It is just a tall Cu with no hazard

Correct Incorrect Correct answer

TCU (towering cumulus) = Cu congestus or Cb in development — ICAO requires reporting alongside height; it indicates potential severe weather

Correct Incorrect Correct answer

It is the same as Ci

Correct Incorrect Correct answer

It has no lightning

Correct Incorrect Correct answer

Stratus drizzle: St produces very small droplets that fall slowly as drizzle (drops <0.5 mm). Full rain requires large drops formed by coalescence in deep clouds or Bergeron process. Drizzle in St is particularly hazardous for icing below 0°C.

Cumulonimbus

Correct Incorrect Correct answer

Stratus — warm process clouds with small droplets produce drizzle; coalescence inefficient for large raindrops

Correct Incorrect Correct answer

Nimbostratus

Correct Incorrect Correct answer

Altostratus

Correct Incorrect Correct answer

Sky obscured: when a surface-based obscuring phenomenon (fog, blowing snow, dust, smoke) prevents an observer from determining cloud base height. METAR reports sky condition as VV followed by vertical visibility in hundreds of feet (e.g. VV005 = 500 ft vertical visibility).

Thin cloud

Correct Incorrect Correct answer

The sky is completely hidden by a surface-based phenomenon (fog, heavy precipitation, dust) — reported as VV/// (indefinite ceiling)

Correct Incorrect Correct answer

Broken cloud

Correct Incorrect Correct answer

Partial cloud only

Correct Incorrect Correct answer

Freezing level sources: (1) SIGWX chart (freezing level contour), (2) radiosonde sounding (T=0°C altitude), (3) NWP grid output, (4) AIRMET/SIGMET if significant, (5) TAF freezing level (some formats). Essential for icing risk assessment on every IFR flight.

METAR only

Correct Incorrect Correct answer

Radiosonde sounding data, SIGWX charts, TAF with freezing level, or NWP model output — all give freezing level forecast

Correct Incorrect Correct answer

Only PIREP

Correct Incorrect Correct answer

Radar only

Correct Incorrect Correct answer

FEW010CB: only 1–2 oktas of Cb at 1,000 ft — but Cb IS the most dangerous cloud. Even a single Cb nearby warrants serious caution. Pilots should check PIREP and SIGMET before proceeding. Low cloud base of 1,000 ft compounds the hazard.

No concern — FEW means little cloud

Correct Incorrect Correct answer

Immediate concern — even 1–2 oktas of Cb at 1,000 ft indicates active thunderstorm potential, severe turbulence risk, and icing

Correct Incorrect Correct answer

Only if visibility is also low

Correct Incorrect Correct answer

Only if temperature is below 0°C

Correct Incorrect Correct answer

Dry microburst: intense downdraft with no rain reaching the surface (virga only). Particularly hazardous because it is invisible on weather radar (no precipitation return) yet produces violent surface-level outflow. Common in arid regions.

Clear area

Correct Incorrect Correct answer

Dry microburst — the downdraft occurs in dry air so precipitation evaporates before reaching the surface, yet the wind hazard remains

Correct Incorrect Correct answer

Storm eye

Correct Incorrect Correct answer

Anvil zone

Correct Incorrect Correct answer

Quiz Summary

Information

Results

Results

Categories

1. Question

2. Question

3. Question

4. Question

5. Question

6. Question

7. Question

8. Question

9. Question

10. Question

11. Question

12. Question

13. Question

14. Question

15. Question

16. Question

17. Question

18. Question

19. Question

20. Question

21. Question

22. Question

23. Question

24. Question

25. Question

26. Question

27. Question

28. Question

29. Question

30. Question

31. Question

32. Question

33. Question

34. Question

35. Question

36. Question

37. Question

38. Question

39. Question

40. Question

41. Question

42. Question

43. Question

44. Question

45. Question

46. Question

47. Question

48. Question

49. Question

50. Question

51. Question

52. Question

53. Question

54. Question

55. Question

56. Question

57. Question

58. Question

59. Question

60. Question

Company

Legal

Connect