Meteorology

Question 1

What is the Dry Adiabatic Lapse Rate (DALR)?

Answer 1

The DALR is 3°C per 1,000 feet (9.8°C/km), the rate at which unsaturated air cools when rising or warms when descending due to pressure changes without heat exchange.

Example: Air at 15°C rising 2,000 feet cools to 9°C (15 - (3 × 2)).

Question 2

What is the Saturated Adiabatic Lapse Rate (SALR)?

Answer 2

The SALR is about 1.5°C per 1,000 feet (5-6°C/km), the rate at which saturated air cools when rising, reduced by latent heat release from condensation.

Example: Saturated air at 15°C rising 2,000 feet cools to 12°C (15 - (1.5 × 2)).

Question 3

How does the DALR affect atmospheric stability?

Answer 3

If the environmental lapse rate (ELR) is less than 3°C per 1,000 feet (e.g., 2°C), dry air is stable and resists rising. If ELR exceeds 3°C, it’s unstable, promoting convection.

Explanation: Stability depends on comparing ELR to DALR for dry air.

Question 4

How does the SALR affect atmospheric stability?

Answer 4

If the ELR exceeds 1.5°C per 1,000 feet (e.g., 2°C), saturated air is unstable, leading to cloud formation and potential thunderstorms. If less, it’s stable.

Explanation: Latent heat release makes moist air more buoyant.

Question 5

What happens when unsaturated air becomes saturated while rising?

Answer 5

It transitions from DALR (3°C/1,000 ft) to SALR (1.5°C/1,000 ft).

Example: Air at 20°C rises 1,000 feet to 17°C (DALR), saturates, then rises another 1,000 feet to 15.5°C (SALR).

Question 6

How does the DALR apply to descending air?

Answer 6

Unsaturated air warms at 3°C per 1,000 feet when descending.

Example: Air at 5°C at 5,000 feet warms to 20°C at sea level (5 + (3 × 5)).

Question 7

Why is the SALR less than the DALR?

Answer 7

Condensation releases latent heat, reducing the cooling rate from 3°C to 1.5°C per 1,000 feet.

Explanation: This heat offsets expansion cooling.

Question 8

What are the height classifications of clouds?

Answer 8

Low: Below 6,500 feet (e.g., stratus, cumulus).
Medium: 6,500–20,000 feet (e.g., altostratus, altocumulus).
High: Above 20,000 feet (e.g., cirrus, cirrostratus).

Question 9

What are the form classifications of clouds?

Answer 9

Stratiform: Layered, stable air (e.g., stratus, nimbostratus).
Cumuliform: Heaped, unstable air (e.g., cumulus, cumulonimbus).

Question 10

What weather is associated with stratus clouds?

Answer 10

Overcast, drizzle or light rain.

Aviation Impact: Poor visibility, stable conditions.

Question 11

What weather is associated with cumulus clouds?

Answer 11

Fair weather if small; heavy showers or thunderstorms if large and unstable.

Aviation Impact: Turbulence risk if towering.

Question 12

What weather is associated with altostratus clouds?

Answer 12

Steady rain or snow (2–5 mm/hr), overcast, often ahead of warm fronts.

Aviation Impact: Icing and visibility reduction.

Question 13

What weather is associated with altocumulus clouds?

Answer 13

Scattered, may signal thunderstorms or a front within 24 hours.

Aviation Impact: Indicates instability aloft.

Question 14

What weather is associated with cirrus clouds?

Answer 14

Fair weather, thin and wispy, but may precede rain in 12–24 hours.

Aviation Impact: Early warning of frontal systems.

Question 15

What weather is associated with cumulonimbus clouds?

Answer 15

Heavy rain (>10 mm/hr), hail, lightning, severe turbulence.

Aviation Impact: Avoid due to extreme hazards.

Question 16

What weather is associated with nimbostratus clouds?

Answer 16

Continuous rain or snow (2–5 mm/hr), thick overcast, low visibility.

Aviation Impact: Prolonged poor conditions.

Question 17

What is clear ice?

Answer 17

Dense, transparent ice from large supercooled droplets (>0.5 mm) freezing slowly, common in warm fronts or cumulonimbus.

Hazard: Reduces lift (e.g., 25% with 1 mm buildup), increases drag.

Question 18

What is rime ice?

Answer 18

Opaque, brittle ice from small supercooled droplets.

Hazard: Blocks sensors, alters aerodynamics.

Question 19

What is mixed ice?

Answer 19

Combines clear and rime ice from varying droplet sizes (0.1–0.5 mm), in transitional zones.

Hazard: Weight and adhesion issues, risks engine failure.

Question 20

What conditions favor clear ice formation?

Answer 20

Temperatures near 0°C to -10°C, large supercooled droplets in nimbostratus or cumulonimbus.

Explanation: Slow freezing allows dense buildup.

Question 21

What conditions favor rime ice formation?

Answer 21

Colder temperatures (-10°C to -20°C), small supercooled droplets in cumulus or freezing fog.

Explanation: Instant freezing creates a porous structure.

Question 22

What are the hazards of icing to aircraft?

Answer 22

Reduces lift, increases drag and weight, alters aerodynamics, blocks sensors or intakes, risking engine failure and control loss.

Aviation Impact: Severe for helicopters due to rotor imbalance.

Question 23

What does WHISTLE stand for in thunderstorm hazards?

Answer 23

Weather, Hail, Icing, Squalls, Turbulence, Lightning, Electricity.

Question 24

What is the Weather hazard in WHISTLE?

Answer 24

Severe conditions (e.g., heavy rain >10 mm/hr, wind shifts) reducing visibility.

Aviation Impact: Disrupts navigation.

Question 25

What is the Hail hazard in WHISTLE?

Answer 25

Hailstones (>2 cm) damage surfaces, engines, and windscreens in cumulonimbus cores. ## Footnote Aviation Impact: Structural failure risk.

Question 26

What is the Icing hazard in WHISTLE?

Answer 26

Rapid clear or mixed ice buildup in updrafts with supercooled water, reducing lift and increasing weight. ## Footnote Aviation Impact: Control loss potential.

Question 27

What are Squalls in WHISTLE?

Answer 27

Sudden wind gusts (>20 kt increase) near the ground, often from downdrafts. ## Footnote Aviation Impact: Risks control loss during takeoff/landing.

Question 28

What is the Turbulence hazard in WHISTLE?

Answer 28

Severe updrafts/downdrafts (>2,000 ft/min) in cumulonimbus, stressing airframes. ## Footnote Aviation Impact: Structural damage or passenger injury.

Question 29

What is the Lightning hazard in WHISTLE?

Answer 29

Strikes (>100,000 volts) damaging electronics, composites, or fuel systems. ## Footnote Aviation Impact: Critical for helicopters with exposed components.

Question 30

What is the Electricity hazard in WHISTLE?

Answer 30

Static discharges (e.g., St. Elmo’s fire) disrupting radio and navigation systems (interference >10 dB). ## Footnote Aviation Impact: Communication loss.

Question 31

What is radiation fog?

Answer 31

Forms on clear, calm nights when ground cools, condensing near-surface moisture. ## Footnote Aviation Impact: Delays morning operations.

Question 32

What is advection fog?

Answer 32

Warm, moist air cools over a cold surface (e.g., sea fog). ## Footnote Aviation Impact: Persistent, affects coastal airfields.

Question 33

What is frontal fog?

Answer 33

Rain from fronts saturates near-surface air. ## Footnote Aviation Impact: Linked to prolonged weather systems.

Question 34

What is steam fog?

Answer 34

Cold air over warm water causes evaporation and condensation. ## Footnote Aviation Impact: Localized, affects inland water areas.

Question 35

What conditions favor radiation fog formation?

Answer 35

Clear skies, light winds. ## Footnote Explanation: Ground loses heat, cooling air to dew point.

Question 36

What is a katabatic wind?

Answer 36

Cold, dense air flows downslope (5–10 kt) due to gravity, often at night. ## Footnote Weather: Frost, valley fog.

Question 37

What is an anabatic wind?

Answer 37

Warm air rises upslope (5–10 kt) due to daytime heating. ## Footnote Weather: Clears fog, improves visibility.

Question 38

What is a sea breeze?

Answer 38

Cool sea air moves inland to replace rising warm land air. ## Footnote Weather: Moist, cooler conditions.

Question 39

What are trade winds?

Answer 39

Steady winds (10–20 kt) from subtropical highs to the equator. ## Footnote Weather: Stable, dry conditions.

Question 40

What are westerly winds?

Answer 40

Mid-latitude synoptic winds (20–40 kt) driven by pressure gradients. ## Footnote Weather: Variable, fronts, depressions.

Question 41

What conditions favor katabatic winds?

Answer 41

Cold, stable air over elevated terrain at night, with clear skies enhancing cooling. ## Footnote Explanation: Gravity drives downslope flow.

Question 42

What is the source region of Arctic Maritime (Am) air, and what is the associated weather?

Answer 42

Source Region: North Pole and Arctic Ocean. Associated Weather: • Brings very cold conditions, especially in winter, with snowy weather dominating. • Temperatures often drop significantly, supporting snow accumulation. • Appears unstable, particularly in summer, leading to thunderstorms. • Cloud formations include cumulonimbus for convective activity and stratiform clouds during snow events. • Precipitation varies seasonally: snow is common in winter, hail or heavy showers occur from October to May, and summer brings intense showers or thunderstorms. • Winds are predominantly northerly, frequently affecting Scotland and coastal areas, blowing with enough force to reduce visibility during precipitation events. • Visibility clears between precipitation events but is reduced during them.

Question 43

What is the source region of Polar Maritime (Pm) air, and what is the associated weather?

Answer 43

Source Region: Northern Canada and Greenland. Associated Weather: • Most common UK air mass, bringing cold, showery weather year-round. • Consistently unstable, supporting cloud formations like cumulus and cumulonimbus for showers, and occasionally nimbostratus for persistent rain. • Precipitation is frequent, with showers dominating—hail and thunder are notable in winter, especially in the west and north, while summer sees heavier showers in eastern England due to land heating. • Winds blow from the northwest or west, maintaining the chilly, brisk feel. • Visibility fluctuates, reduced during showers but clearer between them, showcasing its role in the UK’s variable climate.

Question 44

What is the source region of Polar Continental (Pc) air, and what is the associated weather?

Answer 44

Source Region: Eastern Europe and Russia. Associated Weather: • Delivers some of the UK’s lowest temperatures, often below -10°C at night, with daytime temperatures sometimes remaining below freezing. • Stability depends on its path: a short sea track over the English Channel keeps it stable, resulting in clear skies and severe frosts, while a longer North Sea track adds moisture, making it unstable with showers of rain or snow, especially on the east coast. • Cloud formations range from clear skies in stable conditions to cumulus or cumulonimbus during unstable showers. • Winds blow from the east or northeast. • Visibility is good under clear skies but reduced during precipitation, reflecting its variable nature.

Question 45

What is the source region of Tropical Maritime (Tm) air, and what is the associated weather?

Answer 45

Source Region: Atlantic Ocean, specifically the Azores-Bermuda region. Associated Weather: • Warm and mild, often raising winter temperatures above average, creating a gentle influence. • Stable over cooler waters, leading to low cloud, drizzle, and fog around windward coasts and hills, but can turn unstable inland or in summer, fostering cumulus development. • Cloud formations include stratus and fog in stable conditions, shifting to cumulus if instability arises. • Precipitation features drizzle and light rain, intensifying if unstable. • South-westerly winds drive the moisture. • Visibility is poor near coasts due to fog, improving inland as conditions change, making it a frequent contributor to mild, wet weather.

Question 46

What is the source region of Tropical Continental (Tc) air, and what is the associated weather?

Answer 46

Source Region: North Africa and the Sahara. Associated Weather: • Introduces hot, dry weather to the UK, with daytime temperatures exceeding 30°C and nighttime temperatures ranging between 15-20°C. • Remains stable due to its warm, arid origins, producing few clouds—possibly high-level cirrus. • Precipitation is rare, though occasional showers may carry Saharan dust, an unusual feature leaving orange residue on surfaces. • Winds likely come from the south or southeast, bringing warmth but also dust and pollutants. • Visibility reduces to moderate or poor levels due to dust and pollutants, standing out for its heatwave potential and dusty influence in contrast to the UK’s typical climate.

Question 47

What is a warm front?

Answer 47

Warm air advances over colder air with a shallow slope (~1:150), causing gradual ascent.

Question 48

What weather is associated with a warm front?

Answer 48

Before: Cirrus to altostratus, falling pressure (2 hPa/hr), light rain. During: Nimbostratus, steady rain (2–5 mm/hr), fog, visibility. After: Warmer, humid air, drizzle.

Question 49

What is a cold front?

Answer 49

Cold air undercuts warm air with a steep slope (~1:50), forcing rapid ascent.

Question 50

What weather is associated with a cold front?

Answer 50

Before: Warm, humid air, building cumulus, falling pressure. During: Squalls, heavy showers/thunderstorms, temperature drop (5–10°C). After: Cooler, drier air, good visibility (>10 km).

Question 51

What is an occluded front?

Answer 51

Cold front overtakes warm front, lifting warm air aloft.

Question 52

What weather is associated with an occluded front?

Answer 52

Before: Cirrus and altostratus, like a warm front. During: Mixed rain/snow (1–3 mm/hr), less intense. After: Gradual clearing.

Question 53

What conditions favor warm front development?

Answer 53

Warm, moist air (e.g., Tm) meeting colder, denser air (e.g., Pc), with a depression driving ascent. ## Footnote Explanation: Shallow slope prolongs weather.

Question 54

What does the Blue colour state indicate?

Answer 54

Visibility ≥8 km, cloud base ≥2,500 ft AGL. No operational restrictions.

Question 55

What does the White colour state indicate?

Answer 55

Visibility 5–8 km, cloud base 1,500–2,500 ft AGL. Minor restrictions.

Question 56

What does the Green colour state indicate?

Answer 56

Visibility ≥5 km, cloud base ≥500 ft AGL. Normal operations, light weather (e.g., drizzle).

Question 57

What does the Yellow 1 colour state indicate?

Answer 57

Visibility 1,600–5,000 m, cloud base 200–500 ft AGL. Caution needed.

Question 58

What does the Yellow 2 colour state indicate?

Answer 58

Visibility 800–1,600 m, cloud base 100–200 ft AGL. Significant restrictions.

Question 59

What does the Red colour state indicate?

Answer 59

Visibility <800 m, cloud base <100 ft AGL. Possible airfield closure.

Question 60

How do you calculate pressure altitude (PA)?

Answer 60

PA = elevation + (1013 - QNH) × 30 ft/hPa. ## Footnote Example: Elevation 500 ft, QNH 990 hPa → PA = 500 + (1013 - 990) × 30 = 1,190 ft.

Question 61

How do you calculate density altitude (DA)?

Answer 61

DA = PA + 120 × (actual temp - ISA temp). ## Footnote Example: PA 2,000 ft, actual temp 25°C, ISA temp 11°C → DA = 2,000 +

Question 62

How do you calculate density altitude (DA)?

Answer 62

DA = PA + 120 × (actual temp - ISA temp). ## Footnote Example: PA 2,000 ft, actual temp 25°C, ISA temp 11°C → DA = 2,000 + 120 × (25 - 11) = 3,680 ft.

Question 63

How do you calculate relative humidity (RH)?

Answer 63

RH = (actual vapour / saturation vapour) × 100. ## Footnote Example: At 20°C, actual vapour 10 g/m³, saturation 17 g/m³ → RH = (10 / 17) × 100 ≈ 58.8%.

Question 64

How do you calculate temperature change using DALR?

Answer 64

3°C per 1,000 ft for unsaturated air. ## Footnote Example: Air at 15°C rises 2,000 ft → 15 - (3 × 2) = 9°C.

Question 65

How do you calculate temperature change using SALR?

Answer 65

1.5°C per 1,000 ft for saturated air. ## Footnote Example: Air at 15°C rises 2,000 ft → 15 - (1.5 × 2) = 12°C.

Question 66

What is the ISA temperature at 2,000 feet?

Answer 66

ISA temp at sea level is 15°C, decreasing 1.98°C per 1,000 ft. ## Footnote At 2,000 ft: 15 - (1.98 × 2) ≈ 11°C.

Question 67

How are warm fronts depicted on synoptic charts?

Answer 67

Red semi-circles pointing in the direction of movement. ## Footnote Aviation Impact: Expect prolonged rain, icing.

Question 68

How are cold fronts depicted on synoptic charts?

Answer 68

Blue triangles pointing in the direction of movement. ## Footnote Aviation Impact: Sudden weather changes, turbulence.

Question 69

How are occluded fronts depicted on synoptic charts?

Answer 69

Purple alternating semi-circles and triangles. ## Footnote Aviation Impact: Mixed precipitation, clearing soon.

Question 70

What do isobars indicate on a synoptic chart?

Answer 70

Lines of equal pressure (e.g., 1000 hPa). ## Footnote Tight spacing means strong winds (>30 kt). Aviation Impact: Turbulence risk.

Question 71

What does the 528 line represent on a synoptic chart?

Answer 71

On a 500 hPa chart, 528 dam (5,280 meters) is a threshold where snow is likely below if surface temperatures are near or below 0°C. ## Footnote Indicates a cold upper atmosphere supporting snow.

Question 72

What does the 546 line represent on a synoptic chart?

Answer 72

On a 500 hPa chart, 546 dam (5,460 meters) is a transitional zone; below this, mixed precipitation or snow is likely if surface temperatures are 0–5°C. ## Footnote Above, rain is favored.

Question 73

What does the 564 line represent on a synoptic chart?

Answer 73

On a 500 hPa chart, 564 dam (5,640 meters) indicates warmer air aloft; above this, rain is typical, below it, snow or mixed precipitation increases in winter. ## Footnote Marks a warmer, often tropical air mass.

Question 74

What does a trough indicate on a synoptic chart?

Answer 74

An elongated low-pressure area, shown as a dashed line, linked to showers or thunderstorms. ## Footnote Aviation Impact: Expect instability, turbulence.

Question 75

How is wind depicted on a synoptic chart?

Answer 75

Wind barbs show direction and speed: each full barb = 10 kt, half barb = 5 kt. ## Footnote Example: Two full barbs + half barb = 25 kt.

Question 76

What conditions favor snow below the 528 line?

Answer 76

Surface temperatures near or below 0°C, cold air mass (e.g., Pc or Am), and 500 hPa height ≤528 dam. ## Footnote Cold aloft ensures snow reaches the ground.

Question 77

How does DALR influence cloud base height?

Answer 77

Cloud base occurs where air cools to its dew point at 3°C/1,000 ft. ## Footnote Example: Air at 20°C with dew point 14°C forms clouds at 2,000 ft (20 - 14 = 6°C ÷ 3°C/1,000 ft).

Question 78

What weather is associated with cirrostratus clouds?

Answer 78

Thin, high clouds with a halo effect around the sun/moon, indicating rain within 12–24 hours. ## Footnote Aviation Impact: Early frontal warning.

Question 79

What are the hazards of clear ice to helicopters?

Answer 79

Heavy buildup (e.g., 10 mm/min) on rotors reduces lift, increases drag, and risks imbalance. ## Footnote Aviation Impact: Lethal control loss.

Question 80

What are the hazards of squalls in thunderstorms?

Answer 80

Sudden gusts (>20 kt) from downdrafts risk control loss near the ground. ## Footnote Example: Wind shifts from 10 kt to 35 kt in seconds.

Question 81

What conditions favor advection fog formation?

Answer 81

Warm, moist air moves over a cooler surface.

Question 82

What is the source region of Returning Polar Maritime (RPm) air, and what is the associated weather?

Answer 82

Source Region: Greenland and the Arctic, modified via the North Atlantic. Associated Weather: • Starts cold but warms over the ocean, becoming mild and moist by the time it reaches the UK. • Stability varies by direction: unstable when moving southwards, producing clouds and rain showers, and stable when shifting northeastwards after encountering cooler waters, leading to extensive cloud cover like stratocumulus or altostratus in stable states, or cumulus in unstable ones. • Precipitation includes rain showers, potentially continuous if stable. • Winds likely from the west or southwest drive the weather. • Visibility reduces during precipitation but varies otherwise, reflecting its dynamic transformation over the Atlantic.