Clouds and Precipitation
~9 min read
- Clouds: Visible mass of water droplets/ice. Classified by height (high/middle/low) and shape (cirro-, alto-, strato-, cumulo-, nimbo-).
- Precipitation types: Convectional (rising hot air), Orographic (mountain barriers), Cyclonic/Frontal (along weather fronts).
- Forms: Rain, snow, sleet, hail, dew, frost, fog.
Clouds form when air rises and cools below its dew point, condensing water vapour. Precipitation is the return of water to the surface. NDA tests cloud classification and rainfall types.
Cloud Classification
By height:
| Family | Height | Examples |
|---|---|---|
| High clouds | 5–13 km | Cirrus, Cirrostratus, Cirrocumulus — ice crystals, thin, wispy |
| Middle clouds | 2–7 km | Altostratus, Altocumulus — water + ice mix |
| Low clouds | 0–2 km | Stratus, Stratocumulus, Nimbostratus — water droplets, often produce drizzle/rain |
| Vertical clouds | 0.5–13 km | Cumulus (fair-weather puffs), Cumulonimbus (thunderstorm towers) |
Cirrus — high, thin, wispy (often called "mares' tails"). Cumulus — cotton-like, fair weather. Cumulonimbus — tall storm clouds with thunder, lightning, hail. Nimbostratus — uniform grey rain cloud.
Three Types of Rainfall
| Type | Cause | Example |
|---|---|---|
| Convectional | Hot air rises, cools, condenses (afternoon thunderstorms in equatorial regions) | Equatorial regions; Indian summer afternoon showers (Kalbaisakhi) |
| Orographic | Moist air forced up over a mountain, cools on windward side | Western Ghats (windward Konkan coast, leeward Deccan rain shadow); Cherrapunji |
| Cyclonic (Frontal) | Warm and cold air masses meet at a front | Temperate cyclones in mid-latitudes; some Indian Northeast monsoon rain |
Forms of Precipitation
- Rain: Liquid water drops > 0.5 mm.
- Drizzle: Tiny drops < 0.5 mm.
- Snow: Ice crystals forming when temperature is below freezing.
- Sleet: Frozen raindrops; falls during winter.
- Hail: Ice balls formed in cumulonimbus clouds by repeated up-and-down cycles in strong updrafts.
- Dew: Water vapour condenses on cool surfaces (grass, leaves) at night.
- Frost: Dew that freezes (or vapour that deposits as ice directly).
- Fog: Cloud at ground level — reduces visibility < 1 km.
Humidity and Dew Point
Absolute humidity: Mass of water vapour per unit volume of air (g/m³).
Relative humidity: Actual water vapour as a percentage of maximum possible at that temperature. 100% = saturation; condensation begins.
Dew point: Temperature at which the air becomes saturated. Below dew point, water vapour condenses into dew/fog/clouds.
NDA PYQ Examples
Q: Cherrapunji receives heavy rainfall mainly due to:
(a) Convectional rainfall (b) Orographic rainfall (c) Frontal rainfall (d) Cyclonic rainfall
Answer: (b) Orographic — monsoon winds rise over the Khasi hills.
Q: Which cloud is associated with thunderstorms?
(a) Cirrus (b) Stratus (c) Cumulonimbus (d) Altocumulus
Answer: (c) Cumulonimbus — tall vertical clouds with strong updrafts.
Q: Hailstones are formed in which type of cloud?
(a) Stratus (b) Cumulus (c) Cumulonimbus (d) Cirrus
Answer: (c) Cumulonimbus — strong updrafts repeatedly lift water droplets above freezing level.
Drill Clouds and Precipitation for NDA
NDA-pattern items on Clouds and Precipitation with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
What is the difference between fog and mist?
Both reduce visibility. Fog: visibility < 1 km. Mist: visibility 1–5 km. Both are clouds at ground level.
Why does it not rain in deserts?
Descending air at subtropical high pressure belts (30° N/S) doesn't cool to dew point. Without cooling, water vapour can't condense. Deserts also lack the moisture source (oceans/forests).
How is dew formed?
On clear, calm nights, ground surfaces lose heat by radiation and cool below the dew point of the air above. Water vapour in the air condenses on the cold surface as droplets.
Why is Cherrapunji the wettest place but Mawsynram now wettest?
Both are on the windward side of Khasi hills, Meghalaya. Mawsynram (slightly higher altitude, ~1,400 m) has overtaken Cherrapunji as the rainiest place — both receive ~11,000+ mm annually.
What is rain shadow?
The dry leeward side of a mountain where moisture has been wrung out on the windward side. Examples: Deccan Plateau (leeward of Western Ghats); eastern Tibetan Plateau (leeward of Himalayas).