Local Winds, Air Masses & Fronts – NDA Geography Notes

Introduction

The planetary winds of Chapter 14 govern the broad patterns of global circulation. But at the local and regional scale, a different set of winds operates — shaped by local temperature differences, terrain, and seasonal pressure changes. These are local winds — predictable, named, and often having dramatic effects on the weather and people of the regions where they blow.

This chapter also introduces air masses — large bodies of air with uniform temperature and humidity — and fronts — the boundaries between contrasting air masses where most of the world’s significant weather events occur.

NDA tests this chapter primarily through local wind identification and matching questions. The names of local winds, their regions, and their characteristics — hot or cold, dry or moist — are the most reliably tested facts.

Understand the Topic

Air Masses

An air mass is a large body of air that has roughly uniform temperature and humidity throughout its horizontal extent. Air masses form when air stays over a region long enough to take on the temperature and moisture characteristics of that surface.

Source regions are the areas where air masses form. A good source region must be:

• Large and flat
• Have uniform surface characteristics (all land, all ocean, all ice)
• Have calm or gentle winds so the air stays in place long enough to be modified

The four main types of air mass based on source region:

Maritime Polar (mP) — forms over cold ocean surfaces at high latitudes. Cold and moist.

Continental Polar (cP) — forms over cold land surfaces at high latitudes (Siberia, Canada in winter). Cold and dry.

Maritime Tropical (mT) — forms over warm ocean surfaces in the tropics. Warm and moist.

Continental Tropical (cT) — forms over warm, dry land surfaces in the tropics (Sahara, Arabian Desert). Hot and dry. [NDA tested via CDS]

Fronts

A front is the boundary between two air masses of different temperature and humidity. When a cold air mass meets a warm air mass, they do not mix easily. Instead, they form a sharp boundary — the front. Most precipitation and severe weather occurs along fronts.

The science of fronts was developed largely by Norwegian meteorologists in the early 20th century — sometimes called the Bergen School. [NDA tested via CDS]

Types of fronts:

Cold Front:
A cold air mass pushes into and under a warm air mass. The cold air is denser and acts like a wedge — forcing the warm air steeply upward. This rapid uplift causes:

• Cumulonimbus clouds (tall thunderstorm clouds)
• Heavy rainfall in a narrow belt
• Short, intense precipitation followed by clearing
• Rapid temperature drop after the front passes

Cold fronts move faster than warm fronts. [NDA tested via CDS]

Warm Front:
A warm air mass advances and slides gently over a retreating cold air mass. The warm air rises gradually — creating:

• Widespread, layered clouds (stratus, nimbostratus)
• Steady, light to moderate rainfall over a wide area
• Gradual warming after the front passes

Occluded Front:
When a cold front catches up with a warm front and lifts the warm air completely off the surface. The surface is then occupied by cold air on both sides with the warm air aloft. [NDA tested via CDS]

Stationary Front:
When neither air mass is advancing — the front remains in the same position for days. Produces persistent cloud and light rain. [NDA tested via CDS]

Local Winds

Local winds are winds that are specific to a particular region — caused by local temperature differences, terrain effects, or seasonal pressure patterns rather than global pressure belts.

NDA tests local winds heavily through match-list questions. The key information for each wind is:

1. The name
2. The region where it blows
3. Whether it is hot or cold
4. Whether it is dry or moist

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Hot and Dry Local Winds

Foehn (Föhn):
A warm, dry wind that blows down the northern slopes of the Alps in Europe. It is a classic example of an orographic (mountain-related) wind.

How it forms: Moist air from the Mediterranean rises on the southern slopes of the Alps — cooling and losing moisture as rain. When it descends on the northern side, it warms up rapidly (dry adiabatic rate is faster than moist adiabatic rate). The result is a warm, dry wind on the lee side. This process — warming and drying on the downwind side — is called the Foehn effect and applies to all similar winds worldwide. [NDA tested via CDS]

Chinook:
A warm, dry wind that blows down the eastern slopes of the Rocky Mountains in the USA and Canada. It is the North American equivalent of the Foehn. Its name in Arapaho language means “snow eater” — because it can melt large amounts of snow very quickly. Temperature can rise by 20–30°C in just a few hours when a Chinook arrives. [NDA tested via CDS]

Chinook is a local wind occurring in the USA. [NDA tested via CDS]

Sirocco:
A hot, dry (or sometimes moist) wind that originates in the Sahara Desert and blows northward across the Mediterranean Sea to southern Europe (Italy, Spain). As it crosses the Mediterranean, it picks up moisture and arrives as a hot, humid, oppressive wind. In North Africa it is hot and dry — but by the time it reaches Europe it is warm and moist. [NDA tested via CDS]

Sirocco is the hot wind blowing from Africa toward the Mediterranean coast. [NDA 2007-II | NDA tested via CDS]

Khamsin:
A hot, dry, dusty wind that blows from the Sahara Desert across Egypt and the eastern Mediterranean. It typically blows for about 50 days between March and May (the Arabic word khamsin means fifty). Similar to the Sirocco in origin. [NDA tested via CDS]

Harmattan:
A dry, dusty wind that blows from the Sahara Desert westward and southwestward across West Africa toward the Gulf of Guinea coast. It blows during the winter months (November to March). It carries enormous amounts of dust and dries out vegetation. In the coastal areas of West Africa, it is called the “doctor” because it brings some relief from the humid, oppressive conditions there. [NDA 2007-II | NDA 2011-II | NDA tested via CDS]

Harmattan is the dry, dusty wind blowing from the Sahara Desert toward West Africa. [NDA 2011-II]

Loo:
A hot, dry, and oppressive wind that blows from the west and northwest across the Indo-Gangetic Plain (northern India and Pakistan) during the hot season — May and June. It is a severe heat wind that can cause heatstroke and death if a person is exposed to it for extended periods. [NDA tested via CDS]

Santa Ana:
A hot, dry wind that blows from the high desert interior of California and Nevada toward the Pacific coast of southern California. It occurs in autumn and is notorious for spreading wildfires. [NDA tested via CDS]

Simoom (Samoom):
A hot, dry, suffocating wind that blows across the Arabian Peninsula and the Sahara. It carries large amounts of dust and sand. [NDA tested via CDS]

Brickfielder:
A hot, dry wind that blows from the interior of Australia toward the southeastern coast. [NDA tested via CDS]

Cold Local Winds

Mistral:
A cold, dry, strong wind that blows from the north or northwest down the Rhône Valley in southern France toward the Mediterranean. It blows particularly in winter and spring. It can be very violent and has been known to overturn vehicles and damage crops. [NDA 2007-II | NDA tested via CDS]

Mistral is a cold wind blowing in France. [NDA 2007-II]

Bora:
A cold, dry, powerful wind that blows from the northeast down into the Adriatic Sea — affecting the coastal areas of Croatia, Slovenia, and northeastern Italy (particularly the area around Trieste). It blows from the cold continental interior outward to the relatively warm Adriatic. [NDA tested via CDS]

Blizzard:
A severe winter storm with very cold temperatures, strong winds, and blowing snow — reducing visibility to nearly zero. Associated with polar regions — particularly with Antarctica and the northern interior of North America and Russia. [NDA tested via CDS]

Buran (Purga):
A cold, violent blizzard wind that blows across Central Asia and Siberia (Russia and the surrounding former Soviet republics). In Siberia it is called Purga. [NDA tested via CDS]

Pampero:
A cold, violent wind that blows from the southwest across the Pampas grasslands of Argentina — originating from the cold southern latitudes. [NDA tested via CDS]

Lavante (Levante):
A cold, moist wind that blows from the east across the Strait of Gibraltar — affecting southern Spain. [NDA tested via CDS]

Nor’wester:
In New Zealand, the nor’wester is a warm, dry Foehn-type wind that blows across the Canterbury Plains from the northwest — descending from the Southern Alps. In India (West Bengal and Bangladesh), a nor’wester is a violent pre-monsoon thunderstorm.

Sea Breeze and Land Breeze

Sea breezes and land breezes are examples of diurnal (daily) local winds — they change direction twice a day, driven by the different heating and cooling rates of land and water.

Sea Breeze (day):
During the day, land heats up faster than the adjacent sea. Air over land becomes warm, expands, and rises — creating low pressure. Cooler, denser air from the sea flows in to replace it. Wind blows from sea to land — this is the sea breeze.

Sea breezes are common in the afternoon — when the temperature difference between land and sea is greatest. [NDA tested via CDS]

Land Breeze (night):
At night, land cools faster than the sea. Air over land becomes cooler and denser — creating high pressure. Air from the warmer sea surface is still relatively warm and forms low pressure. Wind blows from land to sea — this is the land breeze.

Land breezes are common in the early morning hours. [NDA tested via CDS]

Why does land heat and cool faster than water?

Land has a lower specific heat capacity than water. Water can absorb large amounts of heat with little temperature change. Land heats up quickly but also cools quickly. Ocean moderates temperature — coastal areas have smaller temperature ranges than continental interiors.

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Mountain Breeze and Valley Breeze

Similar to sea and land breezes but driven by terrain height differences.

Valley Breeze (day):
During the day, mountain slopes heat up faster than the valley floor at the same elevation. Air on slopes warms, rises, and flows up the slope. Wind blows from the valley upward along the slope — this is the valley breeze (or anabatic wind). [NDA tested via CDS]

Mountain Breeze (night):
At night, mountain slopes cool rapidly by radiation. This cold, dense air flows downward along the slopes into the valley — this is the mountain breeze (or katabatic wind). [NDA tested via CDS]

Katabatic wind = cold air flowing down a slope under gravity.

The term katabatic is sometimes applied to larger cold outflow winds as well — like the cold outflow from the Antarctic ice sheet that creates strong winds around Antarctica.

Match List — Local Winds (Most Tested Format)

Wind	Region	Type
Foehn	Alps, Europe	Warm, dry (lee side)
Chinook	Rocky Mountains, USA/Canada	Warm, dry
Sirocco	Sahara → Mediterranean	Hot, dry/moist
Khamsin	Sahara → Egypt	Hot, dry, dusty
Harmattan	Sahara → West Africa	Hot, dry, dusty
Loo	North India/Pakistan	Hot, dry
Santa Ana	Southern California, USA	Hot, dry
Simoom	Arabian Peninsula/Sahara	Hot, dry, dusty
Brickfielder	Interior → SE Australia	Hot, dry
Mistral	Rhône Valley → S. France	Cold, dry, strong
Bora	NE → Adriatic Sea/Croatia	Cold, dry
Blizzard	Polar/sub-polar regions	Cold, snowy
Buran/Purga	Central Asia/Siberia	Cold, violent
Pampero	SW → Pampas, Argentina	Cold