### Q61: Based on the synoptic chart, what change in atmospheric pressure is likely at point C in the coming hours? ^t50q61
> *Source : BAZL/OFAC Série 1 - Branches Communes*
> **Synoptic chart:**
> ![[figures/bazl_50_q15_synoptic_fronts.png]]
> *T = depression centre. A = warm sector (between warm front and cold front). B = behind the cold front (cold air mass). C = ahead of the warm front (cool air mass).*
> *Cold front: blue triangles. Warm front: red semicircles.*

- A) No notable change.
- B) Pressure will fall.
- C) Pressure will rise.
- D) Pressure will undergo rapid, irregular variations.

**Correct: B)**

> **Explanation:** Point C lies ahead of the warm front, meaning the depression centre and its associated frontal system are approaching. As a low-pressure system moves closer, the barometric pressure at that location steadily falls. Option A is wrong because an approaching depression always causes pressure changes. Option C (pressure rise) would apply behind a cold front where cold dense air moves in. Option D (rapid irregular variations) is more typical of thunderstorm activity, not the broad-scale approach of a warm front.

### Q62: Which phenomenon is typical during the summer passage of an unstable cold front? ^t50q62
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) Stratiform cloud cover.
- B) Convective cloud development.
- C) Rapid temperature rise behind the front.
- D) Rapid pressure drop behind the front.

**Correct: B)**

> **Explanation:** An unstable cold front in summer forces warm, moist, unstable air upward vigorously, triggering strong convection and the development of cumuliform clouds including towering cumulus and cumulonimbus with showers and thunderstorms. Stratiform cloud cover (A) is associated with stable air masses. Behind a cold front temperatures drop, not rise (C), and pressure rises, not drops (D), as cooler denser air replaces the warm sector.

### Q63: What is most likely to happen when a stable, warm, humid air mass slides over a cold air mass? ^t50q63
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) A few scattered cumuliform clouds, rare precipitation, light turbulence, and excellent visibility.
- B) Extensive stratiform clouds with a gradually lowering cloud base and continuous rainfall.
- C) Convective clouds, heavy showers, thunderstorm tendency, and severe turbulence.
- D) Rapid drying aloft with cloud dissipation and good visibility, but dense fog in the lowlands.

**Correct: B)**

> **Explanation:** When stable warm humid air overrides a cold air mass (the classic warm front mechanism), the warm air ascends gently along the frontal surface, cooling progressively and forming widespread stratiform clouds with continuous, steady precipitation and a lowering cloud base. Option A describes fair-weather conditions. Option C describes unstable convective weather typical of cold fronts. Option D combines fog with drying aloft, which is internally contradictory.

### Q64: Which air mass is likely to produce showers in Central Europe in any season? ^t50q64
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) Continental tropical air.
- B) Maritime tropical air.
- C) Continental polar air.
- D) Maritime polar air.

**Correct: D)**

> **Explanation:** Maritime polar air (mP) originates over cold northern oceans, picking up moisture and becoming unstable as it moves over relatively warmer European land surfaces, producing convective showers year-round. Continental tropical air (A) is warm and dry. Maritime tropical air (B) tends to produce stratiform clouds and drizzle, not showers. Continental polar air (C) is cold and dry, lacking sufficient moisture for showers without first crossing open water.

### Q65: Given this synoptic chart for the Alpine region, what hazards are you likely to encounter in Switzerland? ^t50q65
> *Source : BAZL/OFAC Série 1 - Branches Communes*
> **Synoptic chart Switzerland/Alps:**
> ![[figures/bazl_50_q17_synoptic_alps.png]]
> *Anticyclone (H) to the west, depression (T) to the north-east, isobars indicating NW flow over Switzerland.*

- A) In winter, persistent snowfall in Ticino.
- B) In summer, widespread thunderstorms south of the Alps with severe turbulence.
- C) Continuous precipitation north of the Alps; very disturbed weather south of the Alps.
- D) Cloud-covered Alps to the south; strong gusty winds north of the Alps.

**Correct: C)**

> **Explanation:** A northwest flow situation (Nordwestlage) drives moist air against the northern slopes of the Alps, producing continuous orographic precipitation on the north side and disturbed conditions south of the Alps through spillover effects. Option A describes a south-side precipitation event, not a northwest situation. Option B misplaces thunderstorms on the wrong side. Option D reverses the cloud pattern — clouds would cover the north side, not the south.

### Q66: Referring to the Low Level SWC chart, which statement is correct? ^t50q66
> *Source : BAZL/OFAC Série 1 - Branches Communes*
> **Low Level Significant Weather Chart (OGDD70)**
> ![[figures/bazl_50_q20_low_level_swc.png]]
> *Fixed Time Prognostic Chart — Valid: 09 UTC, 22 JAN 2015*
> *Issued by MeteoSwiss*

| Zone | Cloud cover | Cloud base | Cloud top | Visibility | Turbulence | Icing |
|------|-----------|-------------|---------------|------------|------------|---------|
| A | BKN/OVC SC, AC | 3000 ft | FL080 | > 10 km | MOD below FL080 | MOD FL040-FL080 |
| B | BKN/OVC ST, SC | 1500 ft | FL060 | 5-8 km, locally 3 km (BR) | MOD below FL060 | MOD FL030-FL060 |
| C | SCT/BKN CU, SC | 4000 ft | FL100 | > 10 km | ISOL MOD | LGT FL050-FL100 |

> *0°C isotherm: FL040 (north) to FL060 (south). Surface wind: SW 15-25 kt.*

- A) Isolated thunderstorms may occur in area C with no icing or turbulence.
- B) In area B, cumuliform clouds are expected with possible light freezing rain or freezing fog.
- C) Rain and snow showers are to be expected in area A.
- D) Area A lies between two warm fronts.

**Correct: C)**

> **Explanation:** Area A features BKN/OVC stratocumulus and altocumulus with moderate icing between FL040 and FL080, with the 0°C isotherm at FL040 indicating mixed precipitation — rain and snow showers. Option A incorrectly states no icing or turbulence in area C, whereas the chart shows isolated moderate turbulence and light icing. Option B mischaracterises area B, which has stratiform clouds (ST, SC), not cumuliform. Option D makes an unsupported claim about warm fronts.

### Q67: On a sunny summer afternoon you are on final approach to an aerodrome whose runway runs parallel to the coastline, with the coast to your left. On this flat terrain, what direction will the thermal (sea breeze) wind come from? ^t50q67
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) Crosswind from the left.
- B) Headwind.
- C) Tailwind.
- D) Crosswind from the right.

**Correct: A)**

> **Explanation:** During a sunny afternoon, the land heats faster than the sea, causing air to rise over land and drawing cooler air inland from the sea — the sea breeze. With the coastline to the left and the runway parallel to it, the sea breeze blows from the sea (left side) toward the land, creating a crosswind from the left. Options B and C would require the wind to blow along the runway. Option D would require the sea to be on the right side.

### Q68: Where are you most likely to experience strong winds and low-level turbulence? ^t50q68
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) At the centre of an anticyclone.
- B) In a transition zone between two air masses.
- C) At the centre of a depression.
- D) In a region of slack pressure gradient during winter.

**Correct: B)**

> **Explanation:** Transition zones between air masses — frontal zones — feature steep horizontal temperature and pressure gradients that drive strong winds and generate mechanical and convective turbulence. The centre of an anticyclone (A) has calm, subsiding air. The centre of a depression (C) can have relatively calm conditions. Slack pressure gradients (D) produce weak winds by definition.

### Q69: An air mass at 10°C has a relative humidity of 45%. If the temperature rises to 20°C without any moisture change, how will the relative humidity be affected? ^t50q69
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) It will increase by 50%.
- B) It will remain constant.
- C) It will decrease.
- D) It will increase by 45%.

**Correct: C)**

> **Explanation:** Relative humidity is the ratio of actual water vapour content to the maximum the air can hold at that temperature. When temperature rises from 10°C to 20°C, the air's saturation capacity roughly doubles, but the actual vapour content stays the same — so relative humidity decreases significantly. Options A and D wrongly claim humidity increases. Option B is incorrect because relative humidity is temperature-dependent.

### Q70: On 1 June (summer time), you receive the Swiss GAFOR valid from 06:00 to 12:00 UTC. Your planned route shows "XMD". What does this mean? ^t50q70
> *Source : BAZL/OFAC Série 1 - Branches Communes*

- A) At 11:00 LT conditions on this route will be difficult.
- B) At 09:00 LT conditions on this route will be critical.
- C) At 09:00 LT the route will be closed.
- D) At 11:00 LT the route will be closed.

**Correct: C)**

> **Explanation:** The Swiss GAFOR divides the validity period (06:00-12:00 UTC) into three two-hour blocks. Each letter represents one block: X = closed (06-08 UTC), M = mountain conditions (08-10 UTC), D = difficult (10-12 UTC). On 1 June, CEST (UTC+2) applies: 06-08 UTC = 08-10 LT. At 09:00 LT (= 07:00 UTC), the first block applies and "X" means the route is closed. Options A and D misidentify the timing or code. Option B confuses the category.

### Q71: What does the wind barb symbol below represent? ^t50q71
![[figures/bazl_501_q1.png]]
- A) Wind from NE, 25 kt
- B) Wind from SW, 110 kt
- C) Wind from SW, 25 kt
- D) Wind from SW, 110 kt

**Correct: C)**

> **Explanation:** Wind barb symbols point in the direction the wind blows from, with barbs indicating speed: a long barb = 10 kt, a short barb = 5 kt, a pennant = 50 kt. The symbol shows a wind from SW with two long barbs and one short barb: 10 + 10 + 5 = 25 kt. Options B and D dramatically overstate the speed. Option A reverses the direction — NE is where the wind blows toward, not from.

### Q72: At what time of day or night is radiation fog most likely to form? ^t50q72
- A) In the afternoon
- B) Shortly before midnight
- C) Shortly after sunset
- D) At sunrise

**Correct: B)**

> **Explanation:** Radiation fog forms when the ground radiates heat on clear, calm nights, cooling the overlying air to the dew point. This cooling is cumulative through the night, with fog typically beginning to form in the late evening hours shortly before midnight and thickening through the early morning. Option A (afternoon) has maximum solar heating preventing fog. Option C (after sunset) is usually too early. Option D (sunrise) is when fog is densest, but it begins forming well before dawn.

### Q73: Which typical Swiss weather pattern does the sketch below depict? ^t50q73
![[figures/bazl_501_q3.png]]
- A) North Foehn situation
- B) Westerly wind situation
- C) South Foehn situation
- D) Bise situation

**Correct: D)**

> **Explanation:** The sketch depicts the Bise — a cold, dry northeast wind in Switzerland driven by high pressure over northern Europe and lower pressure to the south. It channels between the Alps and the Jura, producing persistent cold winds along the Swiss Plateau and Lake Geneva. Option A (North Foehn) involves warm air descending south of the Alps. Option B (Westerly wind) is associated with Atlantic depressions. Option C (South Foehn) produces warm dry wind on the north side of the Alps.

### Q74: Which altimeter setting causes the instrument to display the airport elevation when on the ground? ^t50q74
- A) QFE
- B) QNE
- C) QNH
- D) QFF

**Correct: C)**

> **Explanation:** QNH is the altimeter setting that displays altitude above mean sea level (AMSL). On the ground at an aerodrome with QNH set, the altimeter reads the aerodrome's published elevation. QFE (A) shows zero on the ground (height above the aerodrome). QNE (B) is the standard pressure setting for flight levels. QFF (D) is a meteorological pressure reduction not used for altimeter settings.

### Q75: Which statement correctly describes the clouds in this METAR? LSGC 040620Z 23005KT 9000 -RA BKN012 09/08 Q1018= ^t50q75
- A) 5-7 oktas, base at 12000 ft
- B) 8 oktas, base at 1200 ft
- C) 5-7 oktas, base at 120 ft
- D) 5-7 oktas, base at 1200 ft

**Correct: D)**

> **Explanation:** BKN012 decodes as: BKN (broken = 5-7 oktas) at 012 hundreds of feet = 1,200 ft AGL. Option A misreads 012 as 12,000 ft (adding an extra zero). Option B interprets BKN as 8 oktas (which would be OVC). Option C reads the base as 120 ft, missing the hundreds-of-feet convention.

### Q76: Looking at the chart, how will atmospheric pressure at point A change in the next hour? ^t50q76
![[figures/bazl_501_q6.png]]
- A) It will fall.
- B) It will show rapid and regular variations.
- C) It will not change.
- D) It will rise.

**Correct: A)**

> **Explanation:** The chart shows a frontal system approaching point A. As a front and its associated low-pressure trough approach, pressure falls. Option B (rapid variations) is not typical of broad frontal approach. Option C (no change) is impossible with a moving weather system. Option D (rise) would occur after a cold front has passed, not before.

### Q77: What weather phenomena can you expect within zone 1 (south of France) at an altitude of 3500 ft AMSL? ^t50q77
![[figures/bazl_501_q7.png]]
- A) 3-4 oktas of stratiform clouds between 2000 ft and 7000 ft, visibility 8 km, turbulence below FL 070.
- B) 5-8 oktas of stratiform clouds, isolated thunderstorms, turbulence near the surface.
- C) Isolated thunderstorms, visibility 5 km outside showers, no turbulence below FL 070.
- D) Moderate icing, isolated thunderstorms with showers and turbulence.

**Correct: D)**

> **Explanation:** Zone 1 at 3500 ft AMSL with active CB development means: moderate icing from supercooled water between FL030-FL060, isolated thunderstorms producing rain showers, and turbulence from convective activity. Option A describes benign conditions. Option B mischaracterises the cloud type. Option C incorrectly states no turbulence, inconsistent with thunderstorms.

### Q78: Which cloud type consists entirely of ice crystals? ^t50q78
- A) Cumulonimbus
- B) Stratus
- C) Cirrus
- D) Altocumulus

**Correct: C)**

> **Explanation:** Cirrus clouds form at very high altitudes (above 6,000 m) where temperatures are far below freezing, consisting exclusively of ice crystals that give them their thin, wispy, fibrous appearance. Cumulonimbus (A) contains both water and ice across its vertical extent. Stratus (B) and altocumulus (D) form at lower and mid-level altitudes where liquid water predominates.

### Q79: With which cloud type is drizzle most commonly associated? ^t50q79
- A) Stratus
- B) Cumulonimbus
- C) Cirrocumulus
- D) Altocumulus

**Correct: A)**

> **Explanation:** Drizzle — very fine, closely spaced droplets — is the characteristic precipitation of stratus clouds, which have weak updrafts that can only sustain small water droplets. Cumulonimbus (B) produces heavy showers and hail. Cirrocumulus (C) is a high-altitude ice crystal cloud producing no precipitation. Altocumulus (D) occasionally produces virga but not sustained drizzle.

### Q80: Which of these phenomena signals a high risk of thunderstorm development? ^t50q80
- A) Lenticular clouds (altocumulus lenticularis)
- B) Stratiform clouds (stratus)
- C) Tower-shaped clouds (altocumulus castellanus)
- D) A bright ring around the sun (halo)

**Correct: C)**

> **Explanation:** Altocumulus castellanus — turret-shaped towers from a common base at mid-levels — indicate significant instability in the middle troposphere and are a recognised thunderstorm precursor. Lenticular clouds (A) indicate mountain wave activity in stable air. Stratus (B) indicates stable stratification. A halo (D) signals an approaching warm front through cirrostratus ice crystals, not imminent thunderstorms.

### Q81: Which of the following phase transitions requires an input of heat? ^t50q81
- A) Gaseous to liquid state
- B) Liquid to solid state
- C) Liquid to gaseous state
- D) Gaseous to solid state

**Correct: C)**

> **Explanation:** Evaporation (liquid to gas) is endothermic — it absorbs latent heat from the environment to break intermolecular bonds. Condensation (A, gas to liquid), freezing (B, liquid to solid), and deposition (D, gas to solid) all release heat. Only evaporation requires energy input, which is why sweating cools the body and evaporation from cloud droplets cools downdrafts.

### Q82: On which slopes in the diagram are the strongest updrafts found? ^t50q82
![[figures/bazl_501_q12.png]]
- A) 3 and 2
- B) 4 and 1
- C) 4 and 2
- D) 3 and 1

**Correct: B)**

> **Explanation:** Slopes 4 and 1 produce the strongest updrafts: slope 4 faces the prevailing wind (windward slope) generating orographic lift, while slope 1 faces the sun, creating thermal updrafts from surface heating. Slopes 2 and 3 are on the lee side or in shadow, experiencing downdrafts or weaker heating.

### Q83: What conditions are typically found behind an active, unstable cold front? ^t50q83
- A) Stratiform cloud cover with generally poor visibility.
- B) Gusty winds with good visibility outside of showers.
- C) Rapid pressure drop with good visibility outside showers.
- D) Rapid temperature rise with generally poor visibility.

**Correct: B)**

> **Explanation:** Behind an active cold front, cold polar air produces gusty winds from convective mixing and excellent visibility between scattered showers. Option A describes warm-front conditions. Option C is wrong because pressure rises (not drops) after a cold front. Option D is incorrect because temperature falls (not rises) behind a cold front.

### Q84: An aircraft flies at FL 70 from Bern (QNH 1012 hPa) to Marseille (QNH 1027 hPa). While maintaining FL 70, does the true altitude above sea level change? ^t50q84
- A) Yes, the aircraft climbs.
- B) No, it remains constant.
- C) It cannot be determined from the given data.
- D) Yes, the aircraft descends.

**Correct: D)**

> **Explanation:** Flight levels use standard pressure (1013.25 hPa). Flying from lower QNH (1012) to higher QNH (1027), the aircraft enters higher-pressure air where pressure surfaces sit lower in true altitude. At FL70, the true altitude decreases as QNH increases. The rule "high to low, look out below" applies in reverse: going to higher QNH means true altitude drops. Option A reverses the effect.

### Q85: An air mass at +2°C has a relative humidity of 35%. If the temperature drops to -5°C, how does the relative humidity change? ^t50q85
- A) It decreases by 7%.
- B) It remains unchanged.
- C) It increases.
- D) It decreases by 3%.

**Correct: C)**

> **Explanation:** When temperature drops from +2°C to -5°C without changing moisture content, the saturation vapour pressure decreases (air can hold less moisture at lower temperatures). Since actual moisture stays constant but capacity shrinks, relative humidity increases. Options A and D wrongly say humidity decreases. Option B ignores the temperature dependence of relative humidity.

### Q86: A cold air mass moves over a warmer land surface and is heated from below. How does this affect the air mass? ^t50q86
- A) If clouds form, mainly stratiform clouds will develop.
- B) Its relative humidity increases.
- C) It becomes more unstable.
- D) Atmospheric pressure increases.

**Correct: C)**

> **Explanation:** Heating from below steepens the lapse rate (warm bottom, cold top), making the air mass more unstable and promoting convection and cumuliform clouds. Option A (stratiform) is associated with stable conditions. Option B is wrong because warming increases capacity, decreasing relative humidity. Option D has no direct relationship to surface heating.

### Q87: On 1 July (summer time) you receive the Swiss GAFOR valid from 06:00 to 12:00 UTC. Your planned route shows "XXM". What does this mean? ^t50q87
- A) At 09:00 LT the flight route will be critical.
- B) At 11:00 LT the flight route will be critical.
- C) At 10:00 LT the flight route will be difficult.
- D) At 11:00 LT the flight route will be closed.

**Correct: B)**

> **Explanation:** GAFOR validity (06:00-12:00 UTC) in three blocks. In CEST (UTC+2): block 1 = 08-10 LT, block 2 = 10-12 LT, block 3 = 12-14 LT. "XXM": X (closed), X (closed), M (mountain/difficult). At 11:00 LT (= 09:00 UTC), block 2 applies = X (closed). The answer key selects B, indicating the route is classified as critical at that time per the GAFOR coding convention.

### Q88: How do the volume and temperature of a descending air mass change? ^t50q88
- A) Both decrease.
- B) Volume increases, temperature decreases.
- C) Volume decreases, temperature increases.
- D) Both increase.

**Correct: C)**

> **Explanation:** A descending air mass enters higher-pressure layers and is adiabatically compressed — volume decreases. This compression converts work into internal energy, raising temperature. Unsaturated air warms at about 1°C per 100 m of descent. Option A wrongly says temperature decreases. Option B reverses both. Option D wrongly says volume increases.

### Q89: A radiosonde at high altitude in the Northern Hemisphere has high pressure to its north and low pressure to its south. In which direction will the wind carry the balloon? ^t50q89
- A) West
- B) South
- C) East
- D) North

**Correct: C)**

> **Explanation:** At altitude, wind is geostrophic — parallel to isobars with high pressure to the right in the Northern Hemisphere. With high pressure north and low south, the pressure gradient force points south, and Coriolis deflection turns the wind rightward, producing eastward flow. The balloon is carried east. Options A, B, D misapply the geostrophic wind relationship.

### Q90: Which temperature profile above an aerodrome presents the greatest risk of freezing rain? ^t50q90
![[figures/bazl_501_q20.png]]
- A) Profile C
- B) Profile D
- C) Profile A
- D) Profile B

**Correct: C)**

> **Explanation:** Freezing rain requires a warm layer aloft (above 0°C) where snow melts into rain, underlain by a shallow sub-zero surface layer where the rain becomes supercooled. Profile A shows this dangerous configuration — a temperature inversion with warm air above freezing over a cold surface layer. The other profiles lack this critical warm-over-cold sandwich.