Extreme Wind Phenomena • Mid-Latitude Storms • Frontal Weather Systems
Extratropical cyclones are the giant weather engines of the middle latitudes. They move warm and cold air across continents, generate fronts, produce rain and snow, drive coastal flooding and create many of the world’s most destructive windstorms.
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What is an extratropical cyclone, how does it form, and why do some become violent windstorms? This guide explains baroclinic instability, polar fronts, jet-stream forcing, cyclone life cycles, warm and cold conveyor belts, bombogenesis, sting jets, regional storm types, rain, snow, coastal flooding, forecasting, climate influences, historic windstorms and safety.
An extratropical cyclone is a large rotating low-pressure system that forms outside the tropics, usually where contrasting warm and cold air masses meet. Also called a mid-latitude cyclone, frontal cyclone or temperate cyclone, it draws energy primarily from horizontal temperature differences rather than directly from warm tropical ocean water.
Extratropical Cyclone Quick Facts
- Extratropical cyclones are large low-pressure systems forming outside the tropics.
- They are powered mainly by horizontal temperature contrasts between air masses.
- They commonly form along the polar front in the middle latitudes.
- The jet stream and Rossby waves strongly influence their development and movement.
- Most contain warm fronts, cold fronts or occluded fronts.
- A mature system often appears as a comma-shaped cloud mass on satellite imagery.
- They can produce damaging wind, heavy rain, snow, freezing rain and coastal flooding.
- Bomb cyclones are rapidly intensifying extratropical cyclones.
- Sting jets are narrow descending wind currents inside some powerful cyclones.
- Nor’easters, European windstorms and Bering Sea storms belong to this broad storm family.
- Extratropical cyclones can be much larger than hurricanes.
- They can produce hurricane-force wind without being tropical cyclones.
- The strongest storm season generally occurs from autumn through spring.
- Storm impacts depend on track, pressure gradient, terrain, tides, soil saturation and infrastructure exposure.
What Is an Extratropical Cyclone?
An extratropical cyclone is a rotating low-pressure weather system that develops outside tropical regions.
These storms usually form between approximately 30° and 70° latitude, where warm subtropical air and colder polar air frequently meet.
Extratropical cyclones redistribute heat, moisture and momentum around the planet.
They are responsible for a large share of day-to-day weather across:
- North America;
- Europe;
- northern and eastern Asia;
- southern South America;
- southern Australia;
- New Zealand;
- the North Atlantic;
- the North Pacific;
- the Southern Ocean.
Other Names for Extratropical Cyclones
The same broad storm family is described using several terms.
| Term | Meaning |
|---|---|
| Extratropical cyclone | A cyclone forming outside the tropical belt. |
| Mid-latitude cyclone | A cyclone forming mainly in the middle latitudes. |
| Frontal cyclone | A low-pressure system organized around weather fronts. |
| Temperate cyclone | An older term emphasizing formation in temperate latitudes. |
| Depression | A common European term for a low-pressure system. |
| Winter storm | An impact-based term often used when snow, ice or strong winds dominate. |
| Windstorm | An extratropical cyclone whose main impact is damaging wind. |
These names overlap, but they are not always interchangeable in every forecast or scientific context.
Where Do Extratropical Cyclones Form?
Extratropical cyclones develop most frequently along major mid-latitude storm tracks.
North Atlantic storm track
Storms commonly develop near eastern North America, intensify over the Atlantic and move toward Iceland, the British Isles, Scandinavia or continental Europe.
North Pacific storm track
Powerful cyclones form east of Japan, near the Aleutians and across the Gulf of Alaska before affecting Alaska, western Canada and the western United States.
Mediterranean region
Smaller but sometimes intense cyclones form over the Mediterranean, producing heavy rain, snow, strong winds and coastal flooding.
Southern Ocean
The strong westerlies surrounding Antarctica support frequent and powerful extratropical cyclones.
Continental interiors
Cyclones also develop east of major mountain ranges and over continental temperature boundaries.
What Powers an Extratropical Cyclone?
Extratropical cyclones draw energy mainly from horizontal differences in temperature.
Cold air is dense and warm air is less dense. Where those air masses meet, the atmosphere contains stored potential energy.
A developing cyclone converts part of that potential energy into:
- rising and sinking air;
- cloud formation;
- precipitation;
- rotation;
- strong horizontal wind;
- heat transport toward the poles.
Latent heat
Water-vapor condensation releases heat inside clouds and can strengthen cyclone development.
However, latent heat supplements the storm rather than replacing the primary role of temperature gradients and upper-level dynamics.
Baroclinic Instability: The Main Cyclone Engine
Baroclinic instability develops where temperature changes strongly across a horizontal distance.
In such an atmosphere, surfaces of equal pressure and equal temperature are tilted relative to one another.
Small disturbances along this boundary can amplify into large waves and eventually form rotating low-pressure systems.
Why it matters
Baroclinic instability allows the atmosphere to reduce the contrast between warm and cold regions.
The developing cyclone moves:
- warm air poleward;
- cold air equatorward;
- heat upward;
- momentum through the storm track.
Main Ingredients for Extratropical Cyclone Formation
- A strong temperature gradient: warm and cold air masses positioned close together.
- A surface disturbance: a wave, trough or pressure fall along the frontal boundary.
- Upper-level divergence: air spreading apart above the developing low.
- Jet-stream support: strong upper-level winds helping remove mass from the atmospheric column.
- Moisture: water vapor supporting clouds, precipitation and latent-heat release.
- Coriolis force: planetary rotation helping organize the circulation.
- Time and space: room for the disturbance to deepen and develop a full frontal structure.
How the Jet Stream Helps Cyclones Form
The jet stream is a band of fast-moving wind near the upper troposphere.
It develops near strong horizontal temperature gradients and plays a central role in extratropical cyclone formation.
Jet streaks
A jet streak is a region of especially fast wind embedded within the larger jet stream.
Certain regions near the entrance and exit of a jet streak favor rising motion and surface pressure falls.
Upper-level divergence
When air spreads apart high above a developing surface low, mass is removed from the atmospheric column.
Surface pressure falls and the cyclone deepens.
Storm steering
The jet stream also helps determine:
- storm direction;
- storm speed;
- development region;
- landfall timing;
- whether a cyclone curves poleward or remains zonal.
Rossby Waves and Mid-Latitude Storm Tracks
Rossby waves are large north–south bends in the upper-level westerly winds.
Their troughs and ridges influence where extratropical cyclones form and travel.
Upper-level troughs
Troughs contain colder air aloft and often support rising motion ahead of them.
Surface cyclones frequently deepen east of an upper-level trough.
Progressive patterns
Fast-moving Rossby waves produce a sequence of traveling storms.
Blocking patterns
Blocking highs can redirect cyclones, slow them or force several storms along the same path.
This can create prolonged rain, repeated windstorms or persistent cold and snow.
What Is Cyclogenesis?
Cyclogenesis is the formation or strengthening of a cyclone.
It begins when pressure falls and organized rotation develops around a low-pressure center.
Common cyclogenesis regions
- east of major mountain ranges;
- along the Gulf Stream;
- along the Kuroshio Current near Japan;
- near the polar front;
- over the western Mediterranean;
- near the Aleutian Islands;
- along strong coastal temperature boundaries.
Lee cyclogenesis
Cyclones frequently form east of mountain ranges where airflow descending from high terrain helps create a surface trough or low-pressure center.
The Life Cycle of an Extratropical Cyclone
A typical cyclone develops through several stages.
- Initial frontal disturbance
- Open-wave cyclone
- Deepening and mature low
- Occlusion
- Decay or re-intensification
Real storms do not all follow one perfect textbook sequence, but the lifecycle provides a useful framework.
Stage 1: Initial Frontal Wave
A nearly stationary front separates colder air poleward from warmer air equatorward.
A disturbance creates a wave in the front.
Surface pressure begins falling near the wave crest, and weak cyclonic rotation develops.
Early signs
- increasing cloud;
- pressure falls;
- a developing kink in the front;
- light precipitation near the boundary;
- upper-level divergence.
Stage 2: Open-Wave Cyclone
As the low deepens, distinct warm and cold fronts form.
Warm air moves poleward ahead of the low, while colder air advances equatorward behind it.
Typical structure
- a warm front extending east or northeast;
- a cold front extending south or southwest;
- a warm sector between the two fronts;
- organized rain and cloud bands;
- strengthening surface wind.
Stage 3: Mature Extratropical Cyclone
The cyclone reaches its strongest organized phase when the pressure gradient, wind field and frontal precipitation are well developed.
The mature storm may contain:
- heavy rain ahead of the warm front;
- showers and thunderstorms along the cold front;
- snow in the cold sector;
- a dry slot wrapping toward the center;
- strong winds south and west of the low;
- coastal flooding where winds drive water onshore.
Stage 4: Occlusion
The cold front usually moves faster than the warm front.
Eventually, the cold front catches the warm front and lifts the warm sector away from the surface.
This creates an occluded front.
Does occlusion mean the storm is weak?
Not necessarily.
Some cyclones reach peak wind intensity during or near occlusion, especially when the pressure gradient remains tight or a bent-back front develops.
Stage 5: Cyclone Decay
Once the strongest temperature contrasts are removed from the surface low, the cyclone often begins weakening.
Pressure rises, fronts lose definition and the wind field gradually decreases.
Possible alternatives
A cyclone may:
- merge with another low;
- re-intensify over warmer water;
- become vertically stacked and stall;
- transition into a cut-off low;
- undergo tropical or subtropical transition.
Anatomy of an Extratropical Cyclone
An extratropical cyclone contains much more than a low-pressure center and two fronts.
A mature storm may include:
- a surface low;
- a warm sector;
- a cold sector;
- warm, cold and occluded fronts;
- a triple point;
- a comma cloud;
- a cloud head;
- a dry slot;
- conveyor-belt airstreams;
- strong wind regions;
- possible sting jets;
- rain, snow and convective bands.
The Low-Pressure Center
Surface winds rotate counterclockwise around a Northern Hemisphere low and clockwise around a Southern Hemisphere low.
The lowest pressure does not always coincide with the strongest surface winds.
Maximum wind usually occurs where pressure changes most rapidly over distance.
Central pressure
A very low central pressure indicates a deep cyclone, but storm impact also depends on:
- storm size;
- pressure-gradient distribution;
- track;
- forward speed;
- frontal structure;
- terrain;
- population exposure.
The Warm Sector
The warm sector is the wedge of relatively warm air between the warm front and cold front.
Conditions may include:
- strong southerly winds;
- high humidity;
- low cloud;
- drizzle or rain;
- unseasonably warm temperatures;
- thunderstorms near the cold front.
In powerful cyclones, the warm sector transports substantial heat and moisture toward higher latitudes.
Warm, Cold and Occluded Fronts
Warm front
Warm air rises gradually over cooler air, producing layered cloud and widespread precipitation.
Cold front
Cold air advances beneath warm air and may produce a narrow line of heavy rain, snow, thunderstorms or squalls.
Occluded front
The cold front catches the warm front, lifting the warm air away from the ground.
Bent-back front
In some intense cyclones, part of the frontal boundary curls around the low and produces a region of exceptional wind.
Triple Points and Secondary Cyclone Development
A triple point is where three frontal boundaries meet.
It often marks the intersection of:
- a cold front;
- a warm front;
- an occluded front.
Triple points may support:
- secondary low formation;
- strong thunderstorms;
- tornado development;
- rapid changes in wind direction;
- localized heavy precipitation.
Comma Clouds and Cloud Heads
Mature extratropical cyclones frequently form a comma-shaped cloud pattern.
The broad cloud shield north and west of the low is called the cloud head.
Why the comma shape forms
- Warm moist air rises ahead of the cyclone.
- Cloud wraps around the low-pressure center.
- Dry air intrudes from the southwest or west.
- The frontal cloud band curves around the circulation.
A tightly wrapped cloud head may indicate a mature or rapidly intensifying storm.
Dry Slots and Dry Intrusions
A dry slot is a region of relatively cloud-free or thin-cloud air wrapping into the cyclone.
It is associated with descending dry air from higher levels.
Possible effects
- cloud evaporation;
- stronger surface heating;
- increased instability;
- momentum transport;
- enhanced gusts;
- sting-jet development near the cloud head.
The dry slot should not be interpreted as a harmless break in the storm. It may be adjacent to some of the strongest winds.
The Conveyor-Belt Model of Extratropical Cyclones
Meteorologists often describe cyclone airflow using conveyor belts.
These are broad three-dimensional airstreams moving through the storm.
The main conveyor belts are:
- the warm conveyor belt;
- the cold conveyor belt;
- the dry conveyor belt or dry intrusion.
The Warm Conveyor Belt
The warm conveyor belt is a broad current of warm, moist air moving poleward and upward ahead of the cyclone.
It typically begins near the surface in the warm sector and rises over the warm front.
Weather produced
- thick layered cloud;
- widespread rain or snow;
- latent-heat release;
- atmospheric-river transport;
- heavy precipitation near mountains.
Strong warm conveyor belts can transport enormous quantities of moisture toward high latitudes.
The Cold Conveyor Belt
The cold conveyor belt begins in cooler air north or northeast of the cyclone.
It flows toward the low, often beneath the warm conveyor belt, and wraps around the cyclone center.
Possible impacts
- heavy rain or snow;
- strong winds near the bent-back front;
- blizzard conditions;
- wraparound precipitation;
- coastal wind damage.
The cold conveyor belt can generate destructive wind even when no sting jet is present.
The Dry Conveyor Belt
The dry conveyor belt descends from higher levels on the western or southwestern side of the cyclone.
It forms the dry slot and may bring:
- clearer skies;
- lower humidity;
- stronger mixing;
- convective showers;
- severe gusts;
- enhanced instability behind the cold front.
The Norwegian Cyclone Model
The Norwegian cyclone model describes a frontal wave that develops, deepens and eventually occludes.
Its classic sequence includes:
- stationary front;
- frontal wave;
- open-wave cyclone;
- mature low;
- occlusion;
- decay.
This model remains useful, but not every cyclone follows it precisely.
The Shapiro–Keyser Cyclone Model
The Shapiro–Keyser model describes cyclones with a frontal fracture, bent-back front and possible warm seclusion.
Its major stages include:
- frontal wave;
- frontal fracture;
- bent-back warm front;
- warm-core seclusion.
This structure is especially important in severe European windstorms and sting-jet research.
Why Do Extratropical Cyclones Produce Strong Winds?
Wind forms because air accelerates from higher pressure toward lower pressure.
In a powerful cyclone, closely packed pressure contours create a strong pressure-gradient force.
Destructive wind may come from:
- the broad pressure gradient;
- the cold conveyor belt;
- the warm sector low-level jet;
- post-frontal convection;
- sting jets;
- mountain and gap acceleration;
- boundary-layer mixing.
Pressure Gradients and Wind Strength
A pressure gradient describes how quickly atmospheric pressure changes over distance.
Closely spaced isobars on a weather map indicate a strong gradient and potentially strong wind.
Central pressure is not enough
Two storms with the same minimum pressure can produce different winds because:
- one may be smaller and more tightly packed;
- one may have a broader wind field;
- their tracks may differ;
- their frontal structures may differ;
- terrain may enhance one storm more strongly.
Momentum Transport and Boundary-Layer Mixing
The strongest winds in a cyclone may initially occur hundreds or thousands of meters above the surface.
Turbulence, convection and precipitation can transport this momentum downward.
Strong mixing occurs when:
- cold air moves over a warmer surface;
- sunlight heats the ground behind a front;
- showers create downdrafts;
- dry air increases instability;
- terrain disrupts the flow.
This is why gusts may intensify after a cold front passes even while central pressure begins rising.
How Terrain Enhances Cyclone Winds
Mountains, valleys, coasts and urban landscapes modify the cyclone wind field.
Mountain passes
Air accelerates through gaps and passes aligned with the pressure gradient.
Downslope winds
Cross-mountain flow may produce mountain waves and destructive lee-side gusts.
Coastal exposure
Headlands and open coastlines receive stronger marine wind with fewer surface obstacles.
Urban turbulence
Tall buildings create localized gusts and downdrafts at street level.
Sting Jets Inside Extratropical Cyclones
A sting jet is a narrow current of rapidly descending air inside some intense extratropical cyclones.
It descends from the hooked cloud head near the bent-back front and can create a concentrated corridor of exceptional surface gusts.
Sting-jet ingredients
- a mature Shapiro–Keyser cyclone;
- a hooked cloud head;
- a dry intrusion;
- evaporative cooling;
- slantwise instability;
- strong winds at middle levels;
- efficient downward momentum transport.
Sting jets occur in only a minority of extratropical cyclones.
Bomb Cyclones and Explosive Cyclogenesis
A bomb cyclone is an extratropical cyclone that deepens extremely rapidly.
The process is called bombogenesis or explosive cyclogenesis.
All bomb cyclones are extratropical cyclones, but not all extratropical cyclones are bomb cyclones.
The classic threshold
The commonly cited reference is a central-pressure fall of approximately 24 hectopascals in 24 hours near 60° latitude.
The exact threshold is adjusted for latitude because the Coriolis effect changes between regions.
Why bomb cyclones become dangerous
- rapidly tightening pressure gradients;
- fast wind-field expansion;
- heavy rain or snow;
- high waves;
- storm surge;
- limited preparation time;
- possible sting-jet development.
What Weather Do Extratropical Cyclones Produce?
The same cyclone can produce dramatically different weather across its circulation.
| Storm region | Typical weather |
|---|---|
| Ahead of the warm front | Layered cloud, rain, snow, sleet or freezing rain |
| Warm sector | Strong winds, mild air, low cloud, rain or drizzle |
| Cold front | Heavy rain, squalls, thunderstorms, hail or abrupt temperature drop |
| Behind the cold front | Showers, snow squalls, gusts and falling temperatures |
| Wraparound sector | Heavy rain or snow, strong winds and prolonged precipitation |
| Coast | Storm surge, high waves, erosion and flooding |
Heavy Rain and Inland Flooding
Extratropical cyclones can produce widespread rainfall along fronts and conveyor belts.
Flood risk increases when:
- the storm moves slowly;
- several cyclones follow the same path;
- an atmospheric river feeds the warm conveyor belt;
- mountains force moist air upward;
- soil is already saturated;
- snowmelt occurs simultaneously.
Secondary wind danger
Saturated soil weakens tree-root support, making forests and urban trees more vulnerable to windthrow.
Snowstorms, Blizzards and Wraparound Snow
Extratropical cyclones are responsible for many major snowstorms.
Heavy snow may develop:
- northwest of the low-pressure center;
- along the cold conveyor belt;
- north of the warm front;
- within deformation bands;
- over mountains exposed to moist flow.
Blizzard conditions
Strong wind can combine with falling or loose snow to create:
- whiteouts;
- deep drifting;
- dangerous wind chill;
- road closures;
- power outages.
Freezing Rain and Ice Storms
Freezing rain occurs when snow melts in a warm layer above the ground and then falls into shallow subfreezing air near the surface.
The droplets remain liquid until they strike exposed objects and freeze.
Extratropical cyclones frequently create this vertical temperature structure near warm fronts.
Major impacts
- dangerous roads;
- tree damage;
- power-line failure;
- aircraft icing;
- roof loading;
- long power outages.
Thunderstorms, Squall Lines and Tornadoes
The warm sector and cold front of an extratropical cyclone may support severe convection.
Possible hazards include:
- squall lines;
- supercells;
- tornadoes;
- large hail;
- downbursts;
- derechos;
- flash flooding.
Triple-point tornadoes
Enhanced wind shear near the triple point can create a favorable environment for rotating thunderstorms.
Atmospheric Rivers and Extratropical Cyclones
Atmospheric rivers are long corridors of concentrated water-vapor transport.
They are often connected to the warm conveyor belt of an extratropical cyclone.
Combined impacts
- extreme rainfall;
- mountain snow;
- flooding;
- landslides;
- rapid snowmelt;
- strong pre-frontal winds.
Storm Surge and Coastal Flooding
Extratropical cyclones can produce dangerous coastal water levels through:
- strong onshore wind;
- low atmospheric pressure;
- large waves;
- high astronomical tides;
- long wind fetch;
- coastal geometry.
Why surge can occur far from the storm center
Extratropical cyclones have very large wind fields.
Water may be pushed toward a coastline hundreds of kilometers from the central low.
Marine and Ocean Hazards
Extratropical cyclones are among the most dangerous weather systems for ships and offshore infrastructure.
Hazards include:
- hurricane-force marine wind;
- high seas;
- crossing wave systems;
- rapid pressure changes;
- icing in cold regions;
- poor visibility;
- coastal surge;
- dangerous harbor conditions.
Rapidly deepening storms over the North Atlantic, North Pacific and Southern Ocean are especially hazardous.
Regional Types of Extratropical Cyclones
Different regions use different names for recurring cyclone patterns.
| Regional storm type | Main region | Common hazards |
|---|---|---|
| European windstorm | North Atlantic and Europe | Damaging wind, rain, coastal flooding |
| Nor’easter | Eastern North America | Snow, rain, wind, coastal flooding |
| Alberta Clipper | Canada and northern United States | Fast snow, cold and wind |
| Colorado low | Central North America | Blizzards, thunderstorms and strong winds |
| Great Lakes storm | Great Lakes region | High waves, snow, wind and coastal flooding |
| Aleutian low | North Pacific and Alaska | Marine wind, snow, rain and high waves |
| Bering Sea storm | Alaska and Bering Sea | Storm surge, erosion and hurricane-force wind |
| Southern Ocean cyclone | Mid- and high southern latitudes | Extreme marine wind and waves |
European Windstorms
European windstorms are powerful extratropical cyclones crossing the North Atlantic into western, northern or central Europe.
They commonly affect:
- Ireland;
- the United Kingdom;
- France;
- Belgium;
- the Netherlands;
- Germany;
- Denmark;
- Switzerland;
- Scandinavia.
Why they are so damaging
- dense population;
- extensive forests;
- major transport networks;
- large insurance exposure;
- winter soil saturation;
- coastal infrastructure;
- possible sting jets.
Named storms such as Arwen, Eunice, Franklin, Eleanor, Alex and Amélie belong to this broad family.
North Atlantic Cyclones
The North Atlantic is one of the planet’s most active extratropical storm regions.
Cyclones develop along the contrast between:
- cold continental or polar air;
- milder maritime air;
- warm Gulf Stream waters;
- the powerful North Atlantic jet stream.
Typical tracks
Storms may move toward:
- Newfoundland;
- Greenland;
- Iceland;
- the British Isles;
- Norway;
- western continental Europe.
Nor’easters
A nor’easter is an extratropical cyclone affecting the eastern coast of North America.
Its name comes from the strong northeasterly winds affecting coastal areas ahead of the storm.
Typical impacts
- heavy snow;
- blizzard conditions;
- coastal flooding;
- large waves;
- strong winds;
- heavy rain;
- transport disruption.
Great Lakes Storms
Extratropical cyclones crossing the Great Lakes can produce severe wind, high waves, coastal flooding and heavy lake-enhanced snow.
Important hazards
- dangerous shipping conditions;
- rapid wave growth;
- lake-effect snow behind the cyclone;
- shoreline erosion;
- power outages;
- freezing spray.
The Great Lakes can locally intensify moisture and snowfall but do not create the large cyclone by themselves.
Alberta Clippers
Alberta Clippers are fast-moving extratropical cyclones originating near western Canada.
They usually move southeastward across central Canada and the northern United States.
Typical characteristics
- rapid movement;
- light to moderate snow;
- strong wind;
- abrupt temperature drops;
- dangerous wind chill;
- blowing snow.
Clippers often contain less moisture than Gulf-fed winter storms but can still create severe travel conditions.
Colorado Lows and Panhandle Hooks
Colorado lows form near the central Rocky Mountains and intensify as they move onto the Great Plains.
Panhandle-hook storms follow a curved track from the southern High Plains toward the central United States and Great Lakes.
Possible impacts
- blizzards northwest of the track;
- heavy rain and thunderstorms in the warm sector;
- tornadoes along the cold front;
- strong winds over a broad area;
- rapid temperature changes.
North Pacific Cyclones
The North Pacific produces some of the largest and deepest extratropical cyclones on Earth.
Storms often form east of Japan and intensify while moving toward the Aleutian Islands, Gulf of Alaska or western North America.
Major impacts
- hurricane-force marine wind;
- giant waves;
- atmospheric rivers;
- coastal flooding;
- mountain snow;
- aviation disruption;
- Alaskan coastal erosion.
Aleutian Lows and Bering Sea Storms
The Aleutian low is a recurring region of low pressure over the North Pacific during the cold season.
Individual cyclones moving through this region can become enormous.
Bering Sea impacts
- hurricane-force wind;
- extreme waves;
- coastal flooding;
- village erosion;
- sea-ice movement;
- marine icing;
- transport and fishing disruption.
Southern Ocean Cyclones
The Southern Ocean contains a nearly continuous belt of strong westerly wind and frequent extratropical cyclones.
Storms move through the Roaring Forties, Furious Fifties and Screaming Sixties.
Why the region is so stormy
- few large land barriers;
- strong temperature contrasts;
- persistent westerlies;
- powerful jet-stream flow;
- large uninterrupted ocean fetch.
These storms produce some of the world’s most extreme marine wind and wave conditions.
Medicanes and Hybrid Mediterranean Storms
A medicane is a Mediterranean cyclone with some tropical-like characteristics.
Many begin as ordinary extratropical or upper-level lows before developing:
- a warmer core;
- organized convection;
- a more symmetrical cloud structure;
- an eye-like feature.
Medicanes are not typical extratropical cyclones once their tropical characteristics become dominant, but transition between storm types can occur.
Extratropical Transition and Tropical Transition
Extratropical transition
A hurricane or tropical cyclone may move into the middle latitudes, interact with fronts and become an extratropical cyclone.
During transition, the storm often:
- expands in size;
- develops fronts;
- becomes asymmetric;
- accelerates;
- shifts its strongest wind away from the center.
Tropical transition
Under some conditions, an extratropical or subtropical low can acquire a warm core and become a tropical cyclone.
Storm classification can therefore change during the lifecycle.
How Are Extratropical Cyclones Forecast?
Large cyclones can often be identified several days in advance.
Meteorologists use:
- surface pressure maps;
- upper-air observations;
- satellite imagery;
- weather radar;
- ocean buoys;
- aircraft observations;
- numerical weather models;
- ensemble forecasts;
- impact databases.
Surface Pressure and Frontal Maps
Surface maps show:
- low-pressure centers;
- high-pressure systems;
- isobars;
- warm fronts;
- cold fronts;
- occluded fronts;
- stationary fronts.
Closely packed isobars indicate a strong pressure gradient and potential for strong wind.
Upper-Air and Jet-Stream Analysis
Upper-air charts reveal the atmospheric structure above the surface.
Common forecast levels
- 850 hPa: low-level temperature, moisture and wind;
- 700 hPa: cloud moisture and rising motion;
- 500 hPa: troughs, ridges and vorticity;
- 300–250 hPa: jet streams and jet streaks.
A strengthening upper-level trough west of a surface low often signals further cyclone development.
Satellite Imagery
Satellite images reveal the cyclone’s cloud structure and evolution.
Key features
- comma cloud;
- cloud head;
- dry slot;
- frontal cloud bands;
- convective cells;
- warm seclusion;
- sting-jet signatures.
Rapidly tightening cloud curvature may indicate intensification.
Weather Radar
Radar shows precipitation intensity and movement.
It helps identify:
- rain bands;
- snow bands;
- cold fronts;
- squall lines;
- thunderstorms;
- mesoscale precipitation structures;
- possible wind signatures.
Radar coverage is limited over oceans, where many cyclones intensify.
Numerical Weather Models
Weather models simulate atmospheric motion using physical equations.
Forecasters compare:
- storm track;
- minimum pressure;
- deepening rate;
- frontal position;
- wind gusts;
- rain and snow amounts;
- storm surge;
- possible sting-jet development.
Global vs regional models
Global models capture the large storm system, while higher-resolution regional models resolve terrain, fronts and localized wind maxima more accurately.
Ensemble Forecasting
An ensemble forecast runs the model many times with slightly different initial conditions.
The results help estimate uncertainty.
Ensembles reveal:
- the range of possible tracks;
- the probability of rapid deepening;
- wind-gust uncertainty;
- rain and snow ranges;
- storm-surge risk;
- confidence in timing.
A tight cluster indicates higher confidence. A wide spread means the forecast remains uncertain.
Why Do Cyclone Forecasts Change?
Small errors in the initial atmosphere can grow rapidly.
Forecast uncertainty comes from:
- sparse ocean observations;
- uncertainty in upper-level disturbances;
- complex cloud and precipitation physics;
- storm interactions;
- jet-stream changes;
- rapid cyclogenesis;
- terrain effects;
- small track shifts.
Why track matters
A shift of 100 kilometers can move the strongest wind, heaviest snow or coastal surge into a completely different region.
Warnings and Impact Forecasting
Public warnings may focus on expected impacts rather than the scientific storm classification.
Possible warnings include:
- high-wind warnings;
- storm warnings;
- hurricane-force wind warnings for marine areas;
- blizzard warnings;
- heavy-rain warnings;
- flood warnings;
- coastal-flood warnings;
- ice-storm warnings;
- severe-thunderstorm or tornado warnings.
Historic Extratropical Cyclones and Windstorms
Historic storms reveal how devastating non-tropical windstorms can become.
Important events include:
- the Great Storm of 1703;
- the Columbus Day Storm of 1962;
- the Great Storm of 1987;
- Cyclone Lothar in 1999;
- Cyclone Gudrun in 2005;
- Cyclone Kyrill in 2007;
- Cyclone Xynthia in 2010;
- Storm Arwen in 2021;
- Storm Eunice in 2022;
- many other North Atlantic, Pacific and Bering Sea storms.
The Great Storm of 1703
The Great Storm of 1703 was one of the most severe windstorms documented in the British Isles.
It caused:
- major building damage;
- widespread tree loss;
- shipwrecks;
- coastal flooding;
- thousands of deaths at sea and on land.
The event occurred long before modern observations, but historical evidence indicates an exceptional extratropical cyclone.
The Columbus Day Storm of 1962
The Columbus Day Storm struck the Pacific Northwest in October 1962.
It produced extreme winds from northern California through Oregon, Washington and British Columbia.
Major impacts
- massive forest damage;
- power failures;
- building destruction;
- transport disruption;
- major economic losses.
The storm remains a benchmark for Pacific Northwest windstorm risk.
The Great Storm of 1987
The Great Storm of October 1987 struck southern England and northern France.
It caused exceptional wind damage, widespread tree loss and major power disruption.
Later research identified evidence that a sting jet may have contributed to the narrow corridor of extreme gusts.
Cyclone Lothar in 1999
Lothar crossed France, Switzerland, Germany and neighboring regions on December 26, 1999.
It produced:
- extreme gusts;
- massive forest blowdown;
- power outages;
- transport disruption;
- numerous fatalities.
Lothar remains one of Europe’s most economically damaging windstorms.
Cyclone Kyrill in 2007
Cyclone Kyrill affected large parts of western, central and northern Europe in January 2007.
The storm produced widespread destructive wind across a very large area.
Impacts included:
- rail and air-transport shutdowns;
- power failures;
- forest damage;
- building damage;
- fatal accidents.
Cyclone Xynthia in 2010
Xynthia crossed western Europe in February 2010.
Strong wind combined with high tide and storm surge along the French Atlantic coast.
The resulting coastal flooding caused severe loss of life and demonstrated that water can become the deadliest impact of an extratropical windstorm.
Modern Named European Windstorms
Modern storm-naming systems help communicate risk and improve public awareness.
Recent named extratropical storms have included:
- Storm Eleanor;
- Storm Alex;
- Storm Arwen;
- Storm Franklin;
- Storm Eunice;
- Storm Amélie;
- Storm Christian;
- Storm Xavier.
The storm name does not represent a separate scientific storm category. These systems remain extratropical cyclones.
Extratropical Cyclones and Climate Change
Climate change can influence extratropical cyclones through changes in temperature gradients, atmospheric moisture, sea ice, storm tracks and ocean temperatures.
More atmospheric moisture
Warmer air can contain more water vapor, increasing the potential for heavy precipitation in cyclone systems.
Changing temperature gradients
Arctic warming may weaken some lower-atmosphere temperature contrasts, while upper-atmosphere and ocean changes may affect cyclone development differently.
Storm-track shifts
Some research indicates regional or seasonal shifts in mid-latitude storm tracks.
Snow and rain changes
Warmer temperatures increase the likelihood that precipitation falls as rain rather than snow in marginal climates.
Coastal risk
Rising sea level increases the baseline water level from which extratropical storm surge begins.
Wind uncertainty
Future changes in the most extreme cyclone winds vary by region and remain more uncertain than the increase in atmospheric moisture and coastal flood exposure.
Extratropical Cyclone Comparison Guide
| Storm type | Main energy source | Fronts | Typical structure | Main hazards |
|---|---|---|---|---|
| Extratropical cyclone | Horizontal temperature contrasts | Usually present | Asymmetric, large and frontal | Wind, rain, snow, ice and coastal flooding |
| Bomb cyclone | Same as an extratropical cyclone, but rapidly intensifying | Usually present | Rapid pressure fall and tightening wind field | Extreme wind, heavy precipitation and waves |
| Hurricane | Warm ocean and latent heat | Absent near the mature core | Warm-core and more symmetrical | Wind, surge, rain and tornadoes |
| Nor’easter | Mid-latitude temperature contrast and Atlantic moisture | Present | Coastal extratropical cyclone | Snow, rain, wind and coastal flooding |
| Polar low | Cold air over relatively warm ocean | Weak or small-scale | Compact high-latitude cyclone | Snow squalls, strong wind and marine hazards |
| Medicane | Hybrid or tropical-like processes over the Mediterranean | May weaken or disappear | Compact and sometimes warm-core | Flooding, wind and coastal damage |
| Sting jet | Descending airflow inside an extratropical cyclone | Associated with the bent-back front | Narrow internal wind current | Localized exceptional gusts |
Extratropical Cyclone and Windstorm Safety
Before the storm
- Monitor official weather warnings.
- Secure outdoor furniture, bins and loose objects.
- Charge phones, batteries and emergency lights.
- Prepare for possible power outages.
- Move vehicles away from large trees where possible.
- Check road, rail, ferry and flight information.
- Bring pets indoors.
- Prepare medications and essential supplies.
During strong winds
- Remain inside a sturdy building.
- Stay away from windows and glass doors.
- Avoid forests, parks and tree-lined roads.
- Do not approach downed power lines.
- Avoid unnecessary travel.
- Expect falling roof tiles and airborne debris.
- Use caution near cranes, scaffolding and construction sites.
If driving
- Reduce speed.
- Keep both hands on the wheel.
- Expect crosswinds on bridges and exposed roads.
- Give extra space to high-sided vehicles.
- Avoid flooded roads.
- Leave the road safely if conditions become uncontrollable.
During heavy snow or ice
- Avoid travel when warnings are active.
- Carry winter emergency supplies.
- Prepare for blocked roads and power loss.
- Protect against carbon-monoxide poisoning.
Near the coast
- Stay away from sea walls and exposed beaches.
- Do not approach large breaking waves.
- Follow evacuation instructions for coastal flooding.
- Secure boats before conditions deteriorate.
After the storm
- Watch for weakened trees and hanging branches.
- Avoid damaged structures.
- Treat fallen wires as live.
- Check on vulnerable neighbors when safe.
- Use generators outdoors and away from windows.
Extratropical Cyclone Myths and Misconceptions
| Myth | Reality |
|---|---|
| Extratropical cyclones are weak because they are not hurricanes. | They can produce hurricane-force winds, major flooding and enormous wave fields. |
| Every deep cyclone is a bomb cyclone. | Bomb-cyclone status depends on the rate of pressure fall, not only the minimum pressure. |
| The lowest pressure marks the strongest wind. | The strongest wind usually occurs where the pressure gradient is tightest. |
| Occluded cyclones are always weakening. | Some storms reach peak wind intensity near or after occlusion. |
| Sting jets occur in every European windstorm. | They occur only in a minority of suitable cyclones. |
| European named storms are a separate cyclone type. | The name is used for communication; the storms remain extratropical cyclones. |
| Extratropical cyclones occur only in winter. | They occur year-round, although the strongest are more common during the cool season. |
| Climate change simply means more windstorms everywhere. | Changes differ by region and hazard; heavy precipitation and coastal exposure are clearer trends than universal wind increases. |
Frequently Asked Questions About Extratropical Cyclones
What is an extratropical cyclone?
An extratropical cyclone is a large rotating low-pressure system that forms outside the tropics, usually along a boundary between warm and cold air masses.
Why is it called extratropical?
The term means that the cyclone forms outside the tropical belt, usually in the middle or high latitudes.
What is another name for an extratropical cyclone?
Other names include mid-latitude cyclone, frontal cyclone, temperate cyclone, depression and non-tropical low-pressure system.
How do extratropical cyclones form?
They form when a disturbance develops along a strong temperature boundary and upper-level winds support rising air and falling surface pressure.
What powers an extratropical cyclone?
Its main energy source is the horizontal temperature contrast between warm and cold air masses, supplemented by latent heat released in clouds.
What is baroclinic instability?
Baroclinic instability is a process in which disturbances grow along strong horizontal temperature gradients and develop into large rotating weather systems.
Why do extratropical cyclones have fronts?
They form where contrasting air masses meet. The boundaries become warm, cold, stationary and occluded fronts.
How large is an extratropical cyclone?
Many are more than 1,000 kilometers wide, and the largest systems can cover much of an ocean basin or continent.
How long does an extratropical cyclone last?
A typical cyclone may persist for several days, although some weaken quickly and others remain active for more than a week.
What is the difference between an extratropical cyclone and a hurricane?
Extratropical cyclones are powered mainly by temperature contrasts and usually contain fronts. Hurricanes are warm-core tropical cyclones powered primarily by warm ocean water and organized convection.
Can extratropical cyclones produce hurricane-force winds?
Yes. Powerful extratropical cyclones can produce hurricane-force gusts or sustained marine winds even though they are not hurricanes.
What is a bomb cyclone?
A bomb cyclone is an extratropical cyclone that undergoes explosive cyclogenesis and experiences a very rapid fall in central pressure.
Are all extratropical cyclones bomb cyclones?
No. All bomb cyclones belong to the extratropical-cyclone family, but most extratropical cyclones do not deepen rapidly enough to qualify.
What is a sting jet?
A sting jet is a narrow descending current of air inside some intense extratropical cyclones that can produce a corridor of exceptional surface gusts.
What is a warm conveyor belt?
A warm conveyor belt is a broad stream of warm, moist air that rises ahead of an extratropical cyclone and produces widespread cloud and precipitation.
What is a cold conveyor belt?
A cold conveyor belt is a cooler airstream that flows toward and around the cyclone center and can produce heavy precipitation and strong winds.
What is an occluded front?
An occluded front forms when a faster cold front catches a warm front and lifts the warm sector away from the surface.
What is a nor’easter?
A nor’easter is an extratropical cyclone affecting eastern North America, often producing strong northeasterly wind, heavy snow or rain and coastal flooding.
Where are extratropical cyclones most common?
They are especially common over the North Atlantic, North Pacific, Southern Ocean and major mid-latitude continental storm tracks.
When is extratropical cyclone season?
They occur year-round, but the strongest mid-latitude cyclones are generally most common from autumn through spring.
Can extratropical cyclones cause tornadoes?
Yes. Thunderstorms in the warm sector or near the cold front and triple point can produce tornadoes when instability and wind shear are sufficient.
Can extratropical cyclones cause blizzards?
Yes. Many major blizzards develop on the cold side of extratropical cyclones where strong wind overlaps with heavy or blowing snow.
Can extratropical cyclones cause storm surge?
Yes. Their large wind fields and low pressure can push water toward coastlines and generate major coastal flooding.
How are extratropical cyclones forecast?
Meteorologists use surface maps, weather balloons, satellites, radar, ocean observations, numerical models and ensemble forecasts.
Why do cyclone forecasts change?
Small differences in the storm track, jet stream, upper-level disturbance and moisture can grow with time and change the location of the strongest impacts.
Are extratropical cyclones becoming stronger?
Changes vary by region and season. A warmer atmosphere increases moisture and heavy-rain potential, while future wind and storm-track trends remain more complex.
