GeographyISC Class 11 · Atmospheric Moisture

Dew, Fog, Clouds, Precipitation and Types of Rainfall (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

Dew, frost, fog and clouds are forms of condensation; rain, snow, sleet and hail are forms of precipitation. Rainfall is convectional (heating), orographic (relief, with a rain shadow) or cyclonic (fronts and cyclones). The Western Ghats give heavy windward rain and a rain shadow at Pune.

Notice that rain falls where air is forced up and cools; the far side gets warm, dry sinking air, so Pune lies in a rain shadow.

Illustration drawn for QuestionBuddy.

Understand Dew, Fog, Clouds, Precipitation and Types of Rainfall

Condensation forms.

Dew: droplets on cool surfaces when the dew point is above freezing; clear sky, calm air, high RH, long cold nights.
Frost: when the dew point is below 0 degrees C, vapour changes directly to ice crystals; it damages crops.
Fog: a cloud at ground level with visibility under 1 km; radiation fog on clear calm winter nights, advection fog when warm moist air crosses a cold surface; smog is fog with smoke; mist is thinner with visibility over 1 km.
Clouds: cirrus (high, thin, feathery, ice crystals), cumulus (heaped, convectional), stratus (low layered sheets) and nimbus (rain clouds; cumulonimbus is towering with an anvil top).

Precipitation. Rain (liquid drops above about 0.5 mm); snow (ice crystals when temperature stays below freezing); sleet (frozen raindrops); hail (layered ice from cumulonimbus updrafts, damaging crops, common in pre-monsoon thunderstorms); drizzle (very fine rain from stratus).

Rainfall types. Convectional: intense heating, strong convection, cumulonimbus, afternoon thunder showers; equatorial regions; Kalbaisakhi in West Bengal and Assam. Orographic: moist winds forced up a mountain give heavy windward rain; the leeward side is a rain shadow with warm, dry descending air; Western Ghats and Pune; Mawsynram and Sohra on the Meghalaya plateau. Cyclonic (frontal): warm moist air lifted over cold air along fronts, or converging around tropical cyclones; western disturbances bring winter rain to the north-west and tropical cyclones bring rain to the east coast.

Dew, Fog, Clouds, Precipitation and Types of Rainfall: key facts

Condensation forms: $D e w ∣ F r os t ∣ F o g ∣ C l o u d$
Precipitation: $R ain ∣ S n o w ∣ S l ee t ∣ H ai l ∣ D r i z z l e$
Rainfall types: $C o n v ec t i o na l : h e a t in g ∣ O r o g r a p hi c : m o u n t ain s ∣ C y c l o ni c : f r o n t s$
Rain-shadow percentage: $L ee w a r d / w in d w a r d x 100∣ F a l l = 100 - t hi s v a l u e$

How to answer Dew, Fog, Clouds, Precipitation and Types of Rainfall questions

Questions are 3 to 4 marks: list forms, explain a rainfall type with a diagram, or compare windward and leeward.

1Name the type of rainfall and the cause of rising air.
2Describe the cooling, condensation and cloud stage.
3Add a regional example.
4For rain-shadow sums, compute leeward as a percentage of windward.

Dew, Fog, Clouds, Precipitation and Types of Rainfall in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Windward and leeward

Suppose a windward town gets 2,400 mm and a leeward town 480 mm.

Express leeward rainfall as a percentage of windward and the reduction.

Try it first, then show the solutionSolution

480/2,400 x 100 = 20 per cent.
Reduction = 100 - 20 = 80 per cent.

Answer: 20 per cent; 80 per cent less.

Memory hook: Leeward over windward.

Cold morning

Suppose a clear still night leaves grass wet with droplets in autumn and white crystals in winter.

Name each deposit.

Try it first, then show the solutionSolution

Above freezing the droplets are dew.
Below 0 degrees C vapour changes to ice crystals: frost.

Answer: Dew in autumn; frost in winter.

Memory hook: Dew liquid, frost ice.

Tricks to remember Dew, Fog, Clouds, Precipitation and Types of Rainfall

Short memory aids. Say each one aloud once, then use it on a question the same day.

CSN
Cirrus high, Cumulus heaped, Stratus layered, Nimbus rain.
Use it when: Clouds.
COC
Convectional heating, Orographic mountains, Cyclonic fronts.
Use it when: Rainfall types.

Dew, Fog, Clouds, Precipitation and Types of Rainfall: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Hail source · 1 mark · MCQBoard level

Hailstones form in:
(a) cirrus
(b) stratus
(c) cumulonimbus
(d) altostratus

Try it first, then show the solutionSolution

Tall storm clouds.

Answer: (c) Cumulonimbus.

Example 2: Fog and mist · 2 marks · Short answerBoard level

Distinguish between fog and mist on visibility.

Try it first, then show the solutionSolution

Fog: visibility below 1 km.
Mist: visibility above 1 km and thinner.

Answer: Fog under 1 km; mist over 1 km.

Example 3: Rain-shadow sums · 4 marks · Long answerHarder board level

A windward station on a mountain range receives 2,000 mm of rain and a leeward station 700 mm. Find the leeward rainfall as a percentage of windward and the percentage reduction. Explain why the leeward side is drier.

Try it first, then show the solutionSolution

700/2,000 x 100 = 35 per cent.
Reduction = 100 - 35 = 65 per cent.
Air loses moisture while rising on the windward side.
Descending leeward air warms by compression and is dry.

Answer: 35 per cent of windward; 65 per cent less; descending dry air.

Example 4: Convectional rain · 4 marks · Long answerHarder board level

Describe the formation of convectional rainfall and name two regions or phenomena.

Try it first, then show the solutionSolution

Intense heating warms the air above the ground.
Air rises in convection currents, cools and forms cumulonimbus.
Heavy showers with thunder fall in the afternoon.
Equatorial regions and Kalbaisakhi of West Bengal and Assam.

Answer: Heating, rising, cooling and cumulonimbus give afternoon showers; equatorial regions and Kalbaisakhi.

Example 5: Rain-type analysis · 5 marks · Case-basedHOTS / competency

Case: A coastal hill town gets heavy monsoon rain, while a town on the opposite side of the range is dry; later a tropical cyclone brings heavy rain to both. (a) Name the first type. (b) Name the dry zone. (c) Name the type linked with the cyclone.

Try it first, then show the solutionSolution

(a) Orographic rainfall.
(b) A rain-shadow area on the leeward side.
(c) Cyclonic (frontal or converging) rainfall.

Answer: (a) Orographic (b) rain shadow (c) cyclonic rain.

Where students lose marks in Dew, Fog, Clouds, Precipitation and Types of Rainfall

The slips examiners see most often, and what to write instead.

Mistake: Mixing dew and frost
Temperature below freezing is ignored.
Do this: Dew forms above freezing; frost when the dew point is below 0 degrees C.
Usually costs: 1 mark.
Mistake: Saying orographic rain falls on the leeward side
Windward and leeward swapped.
Wrong working
Rain-shadow on the windward
Right working
Rain-shadow on the leeward
Do this: Heavy rain is on the windward side; leeward is rain shadow.
Usually costs: 1 to 2 marks.
Mistake: Missing example
Types of rain without places.
Do this: Add Western Ghats, Mawsynram or Kalbaisakhi.
Usually costs: 1 mark.

Exam tips

Draw a profile for orographic rain.
Give leeward as percentage of windward.
List cloud types with heights.
Mention smog as polluted fog.

Practice questions on Dew, Fog, Clouds, Precipitation and Types of Rainfall

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Dark, towering clouds with an anvil top that bring thunder are:
(a) cirrus
(b) stratus
(c) cumulonimbus
(d) cumulus
Hint
Thunderstorm clouds.
Answer
(c) Cumulonimbus.
Q2 · 3 marks · Short answerHarder board level
Explain how hail forms and why it is harmful.
Hint
Updrafts add ice layers.
Answer
Strong updrafts carry raindrops repeatedly into freezing parts of cumulonimbus, adding layers of ice until the stones fall. Hail damages crops, orchards and property.
Q3 · 3 marks · Short answerHarder board level
Why do places on the leeward side of the Western Ghats such as Pune receive less rain?
Hint
Rain shadow.
Answer
Moist south-west monsoon winds give heavy rain on the windward slopes; air descending the leeward side warms by compression and is dry, creating a rain shadow.
Q4 · 3 marks · Short answerHarder board level
A leeward town gets 600 mm while the windward gets 3,000 mm. Find the percentage the leeward rainfall is of windward.
Hint
600/3,000.
Answer
600/3,000 x 100 = 20 per cent.
Q5 · 4 marks · Case-basedHOTS / competency
Case: Two foggy mornings are reported, one on a calm winter night inland and one by the sea where warm moist air crosses cold water. (a) Name each type. (b) Explain the cause of each. (c) Name the polluted form of fog.
Hint
Radiation and advection.
Answer
(a) Radiation fog and advection fog. (b) Ground cooling on a clear calm night, and warm moist air cooled by a cold surface. (c) Smog.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Rain-shadow side?Show answer
Leeward.
2.Kalbaisakhi is?Show answer
Convectional pre-monsoon thunderstorm.
3.Fog visibility?Show answer
Below 1 km.
4.Frozen raindrops?Show answer
Sleet.
5.Cloud with anvil top?Show answer
Cumulonimbus.

Dew, Fog, Clouds, Precipitation and Types of Rainfall: frequently asked questions

Why does the leeward side warm?

Descending air is compressed.

Which rain is typical at the equator?

Convectional.

What is drizzle?

Very fine rain from low stratus clouds.