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DGCA Aviation Meteorology · 94 questions

Temperature, Humidity & Cloud Base: DGCA Aviation Meteorology Questions and Answers

94 practice questions on Temperature, Humidity & Cloud Base with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.

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About this topic

Use this page to revise Temperature, Humidity & Cloud Base for the DGCA Aviation Meteorology paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 94 questions in the TrueHeading bank for this topic.

In short: Use the dew-point spread. The temperature falls 3 °C per 1000 ft and the dew point 0.5 °C, so they close 2.5 °C per 1000 ft.

Open the full set in the student zone to answer every question, track your accuracy and take timed mock tests.

Key concepts: Temperature, Humidity & Cloud Base

5 ideas to know cold.

How do you estimate cloud base?

Use the dew-point spread. The temperature falls 3 °C per 1000 ft and the dew point 0.5 °C, so they close 2.5 °C per 1000 ft.

Cloud base (ft)≈400×(T−Td)\text{Cloud base (ft)}\approx 400\times(T-T_d)
or  122×(T−Td) m\text{or }\ 122\times(T-T_d)\ \text{m}
  • T = 24 °C, Td = 14 °C: spread 10, base ≈ 4000 ft above the surface
T 24 °CTd 14 °CT −3 °C / 1000 ftTd −0.5 °C/ 1000 ftcloud baseBase (ft) ≈ 400 × (T − Td)4000 ft

What are dew point and relative humidity?

Dew point is the temperature at which the air becomes saturated. Relative humidity is the vapour present as a percentage of the most the air could hold at that temperature.

  • When T = Td, RH is 100 % (saturation)
  • Cooling raises RH; warming lowers it
  • Warm air can hold more vapour than cold air

What is an inversion and where do you see them?

A layer where temperature increases with height.

  • Radiation inversion: clear calm night, near the ground
  • Advection, subsidence (in anticyclones) and frontal inversions
  • Very stable: traps smoke, haze and low cloud, and can cause fog

When is the temperature at its daily extremes?

Maximum about 1–2 hours after local noon. Minimum around sunrise.

  • Cloud cover and wind reduce the daily range
  • Dry air and clear skies increase it

Four ways heat moves in the atmosphere?

Radiation, conduction, convection (vertical) and advection (horizontal), plus latent heat from phase changes.

Tip: The atmosphere is warmed mostly from below by the Earth’s surface, not directly by the Sun.

Practice questions: Temperature, Humidity & Cloud Base

Tap “Show answer” after you have tried each one.

Q1Surface temperature 14 °C and dew point 11 °C. The approximate height of the base of cumuliform cloud formed by convection (above the surface) is:

  1. 1 200 ft
  2. 750 ft
  3. 2 400 ft
  4. 3 000 ft
Show answer

Answer: A. 1 200 ft

Spread = 14 − 11 = 3 °C. Base ≈ 400 ft × spread = 1 200 ft (DALR 3 °C/1 000 ft minus dew-point fall of 0.5 °C/1 000 ft leaves 2.5 °C of closure per 1 000 ft).

Q2Surface temperature 20 °C and dew point 8 °C. The approximate height of the base of cumuliform cloud formed by convection (above the surface) is:

  1. 3 000 ft
  2. 12 000 ft
  3. 6 000 ft
  4. 4 800 ft
Show answer

Answer: D. 4 800 ft

Spread = 20 − 8 = 12 °C. Base ≈ 400 ft × spread = 4 800 ft (DALR 3 °C/1 000 ft minus dew-point fall of 0.5 °C/1 000 ft leaves 2.5 °C of closure per 1 000 ft).

Q3Surface temperature 15 °C and dew point −1 °C. The approximate height of the base of cumuliform cloud formed by convection (above the surface) is:

  1. 6 400 ft
  2. 4 000 ft
  3. 7 600 ft
  4. 16 000 ft
Show answer

Answer: A. 6 400 ft

Spread = 15 − −1 = 16 °C. Base ≈ 400 ft × spread = 6 400 ft (DALR 3 °C/1 000 ft minus dew-point fall of 0.5 °C/1 000 ft leaves 2.5 °C of closure per 1 000 ft).

Q4Cloud base from convection is observed at 2800 ft above the surface and the surface temperature is 24 °C. The dew point at the surface is approximately:

  1. 10 °C
  2. 20 °C
  3. 17 °C
  4. 16 °C
Show answer

Answer: C. 17 °C

Spread = base ÷ 400 = 7 °C. Dew point = 24 − 7 = 17 °C.

Q5Cloud base from convection is observed at 2800 ft above the surface and the surface temperature is 14 °C. The dew point at the surface is approximately:

  1. 10 °C
  2. 6 °C
  3. 7 °C
  4. 0 °C
Show answer

Answer: C. 7 °C

Spread = base ÷ 400 = 7 °C. Dew point = 14 − 7 = 7 °C.

Q6Surface temperature 27 °C, dew point 19 °C. A rising parcel cools at the DALR (3 °C/1 000 ft) up to the condensation level (spread × 400 ft). Its temperature at that level is:

  1. 22.2 °C
  2. 27.0 °C
  3. 17.4 °C
  4. 19.0 °C
Show answer

Answer: C. 17.4 °C

Condensation level = 8 × 400 = 3200 ft. Cooling = 3 × 3.2 = 9.6 °C. Temperature = 27 − 9.6 = 17.4 °C.

Q7Surface temperature 20 °C, dew point 13 °C. A rising parcel cools at the DALR (3 °C/1 000 ft) up to the condensation level (spread × 400 ft). Its temperature at that level is:

  1. 20.0 °C
  2. 11.6 °C
  3. 13.0 °C
  4. 15.8 °C
Show answer

Answer: B. 11.6 °C

Condensation level = 7 × 400 = 2800 ft. Cooling = 3 × 2.8 = 8.4 °C. Temperature = 20 − 8.4 = 11.6 °C.

Q8The surface temperature is 24 °C and the temperature falls at 2 °C per 1 000 ft (ISA, rounded). The height of the freezing level above the surface is approximately:

  1. 24 000 ft
  2. 8 000 ft
  3. 13 800 ft
  4. 12 000 ft
Show answer

Answer: D. 12 000 ft

Height = temperature ÷ lapse rate = 24 ÷ 2 = 12.0 thousand ft = 12 000 ft.

Q9The temperature-dew point spread at the surface is 3 °C. Taking 125 m for each °C of spread, the convective cloud base is about:

  1. 750 m
  2. 180 m
  3. 375 m
  4. 1200 m
Show answer

Answer: C. 375 m

Base ≈ 3 × 125 m = 375 m (equivalent to 400 ft per °C).

Q10If the temperature of a parcel of air falls with no change in water vapour content, the relative humidity:

  1. decreases
  2. increases
  3. becomes zero
  4. stays the same
Show answer

Answer: B. increases

Colder air can hold less vapour, so the RH rises.

Q11On a clear night with light wind the temperature falls fastest:

  1. in the stratosphere
  2. at 1 000 m
  3. close to the ground
  4. over the sea
Show answer

Answer: C. close to the ground

Terrestrial radiation cools the surface, giving a ground inversion.

Q12An isothermal layer is one in which the temperature:

  1. decreases at 6.5 °C/km
  2. decreases at the DALR
  3. increases with height
  4. is constant with height
Show answer

Answer: D. is constant with height

Isothermal layers are stable.

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