Strange Weather Phenomena • Winter Weather • Ice Storms
Ice storms are winter’s silent wrecking ball: ordinary-looking rain falls from the sky, then turns roads, forests and power lines into a glass-coated disaster zone.
What causes an ice storm? How does freezing rain differ from sleet, snow, freezing drizzle and black ice? This guide explains the atmospheric warm layer known as the warm nose, shallow surface cold, supercooled liquid water, glaze-ice formation, ice accretion, cold-air damming, road and aviation icing, tree and power-grid failure, forecasting challenges, regional ice-storm patterns, safety and the correct destination for legacy freezing-rain articles.
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This pillar owns freezing rain, ice storms, glaze ice, freezing drizzle, black-ice formation from liquid precipitation and damaging ice accretion. For the complete snow, ice and winter-cyclone system, begin with
Winter Weather Explained.
Broad snow disasters belong under
Blizzards and Major Snowstorms.
Freezing rain is liquid precipitation that remains supercooled below 0°C and freezes when it strikes a subfreezing surface. An ice storm occurs when enough freezing rain accumulates to create widespread or damaging glaze ice on roads, trees, power lines, aircraft, towers and buildings. Unlike a blizzard, an ice storm may arrive quietly—with no dramatic wall of snow—while simultaneously attacking mobility, electricity and communications.
Ice Storms and Freezing Rain: Quick Facts
- Freezing rain reaches the ground as liquid water and freezes after impact.
- Sleet or ice pellets freeze before reaching the ground.
- Snow generally remains frozen from cloud to surface.
- The classic freezing-rain profile contains cold air aloft, a warm layer that melts snow and a shallow subfreezing layer near the ground.
- The warm layer aloft is often called a warm nose.
- The near-surface cold layer must be shallow enough that liquid drops do not refreeze into sleet before reaching the ground.
- Freezing rain can occur when air temperature is slightly above freezing if exposed surfaces remain below freezing.
- Glaze ice is smooth, dense and often transparent.
- Black ice is a thin, hard-to-see surface coating; it is not a separate precipitation type.
- Freezing drizzle contains smaller droplets than ordinary freezing rain.
- Light freezing drizzle can create severe road hazards without dramatic radar returns.
- Ice accumulation depends on precipitation rate, wind, droplet size, surface temperature and runoff.
- The amount of liquid precipitation does not equal the final radial ice thickness on wires and branches.
- Wind can produce greater ice loading on the windward side of exposed objects.
- Ice-covered branches may fail hours after precipitation ends.
- Power outages often result from combined tree, line, pole and wind loading.
- Cold-air damming frequently supports ice storms east of mountain ranges.
- Bridges and overpasses often freeze before ground-supported roads.
- Freezing rain is especially dangerous for aviation because supercooled droplets can freeze onto aircraft.
- A small temperature error can shift a forecast between snow, sleet, freezing rain and rain.
What Is an Ice Storm?
An ice storm is a winter-weather event in which freezing rain accumulates on exposed surfaces and produces significant or damaging glaze ice.
The defining hazard is not the depth of snow. It is the accumulation of dense ice on:
- roads and bridges;
- trees and vegetation;
- power and communication lines;
- utility poles and transmission towers;
- vehicles and aircraft;
- buildings and exposed infrastructure.
Ice storms may cause:
- nearly frictionless roads;
- mass vehicle crashes;
- pedestrian injuries;
- widespread tree failure;
- multi-day or multi-week power outages;
- airport and railway closures;
- communication failure;
- dangerous falling ice after the storm.
What Is Freezing Rain?
Freezing rain is liquid rain that falls through a shallow layer of subfreezing air and freezes when it contacts a sufficiently cold surface.
It commonly begins as snow high in the atmosphere. The snowflakes then:
- fall into a layer of air above freezing;
- melt partially or completely into liquid drops;
- enter a shallow subfreezing layer near the surface;
- remain liquid because the cold layer is too shallow for complete refreezing;
- freeze after striking roads, trees, wires or other cold objects.
These drops are described as supercooled because they remain liquid at temperatures below the normal freezing point.
How Freezing Rain and Ice Storms Form
The classic freezing-rain profile contains several vertical layers.
-
Cold cloud layer:
Precipitation begins as snow or ice crystals. -
Warm layer aloft:
Snowflakes melt into liquid raindrops. -
Shallow cold layer near the ground:
The liquid drops cool below 0°C but do not have enough time to freeze into ice pellets. -
Subfreezing surfaces:
Drops freeze on impact. -
Persistent precipitation:
Repeated impacts build a coating of glaze ice.
Ice-storm severity increases when:
- freezing rain persists for many hours;
- surface temperatures remain below freezing;
- precipitation rates are high enough to accumulate but not so high that excessive runoff occurs;
- wind drives droplets against exposed objects;
- trees retain leaves or weak branches;
- ice accumulation overlaps with strong wind;
- cold air remains trapped near the surface.
The Warm Nose and Shallow Cold Layer
Meteorologists often call the above-freezing layer aloft a warm nose.
Its depth and temperature determine whether falling snow:
- remains snow;
- partially melts;
- fully melts into rain.
Deep surface cold favors sleet
When the near-surface cold layer is deep enough, melted drops refreeze before reaching the ground and become sleet or ice pellets.
Shallow surface cold favors freezing rain
When the cold layer is shallow, drops remain liquid until they strike a cold surface.
Surface warming changes freezing rain to rain
If the surface cold layer erodes completely, precipitation falls as ordinary rain.
What Does Supercooled Mean?
A supercooled droplet is liquid water that remains unfrozen even though its temperature is below 0°C.
Liquid water does not always freeze instantly at the nominal freezing point. Freezing is promoted by:
- contact with an ice nucleus;
- collision with a frozen surface;
- mechanical disturbance;
- sufficiently low temperature;
- contact with existing ice.
When a supercooled raindrop strikes a road, branch, wire or aircraft, freezing begins rapidly and adds to the growing ice layer.
Snow vs Sleet vs Freezing Rain vs Rain
| Precipitation | Atmospheric profile | State at impact | Main hazard |
|---|---|---|---|
| Snow | Mostly below freezing from cloud to ground | Frozen crystals | Accumulation, drifting and reduced visibility |
| Sleet or ice pellets | Warm layer melts snow; deep cold layer refreezes drops | Frozen pellets | Dense, slippery accumulation |
| Freezing rain | Warm layer melts snow; shallow cold layer supercools drops | Liquid until impact | Glaze ice, black ice, tree and power damage |
| Rain | Above-freezing layer reaches the surface | Liquid | Flooding and wet-road hazards |
Freezing Drizzle
Freezing drizzle consists of very small supercooled liquid drops that freeze on contact with exposed surfaces.
It differs from ordinary freezing rain mainly in droplet size and cloud microphysics.
Why freezing drizzle is dangerous
- It may appear insignificant.
- It can create a thin but extremely slippery glaze.
- It may be difficult to detect with radar.
- Drivers may not realize roads are icing.
- It creates serious aircraft-icing hazards.
- It can persist beneath shallow low clouds.
A light precipitation rate does not mean a light impact when every drop freezes onto the road.
What Is Glaze Ice?
Glaze ice is a smooth, dense, often transparent coating formed when supercooled rain or drizzle freezes on contact.
Glaze characteristics
- smooth or glass-like surface;
- high density;
- strong bonding to exposed objects;
- significant structural weight;
- difficult removal;
- continued growth during persistent precipitation.
Glaze vs rime
| Feature | Glaze ice | Rime ice |
|---|---|---|
| Main source | Freezing rain or large supercooled droplets | Freezing fog or cloud droplets |
| Appearance | Smooth, dense and transparent or translucent | White, opaque, rough or feathery |
| Freezing process | Water can spread before freezing | Droplets freeze rapidly on impact |
| Main hazard | Heavy loading and slippery surfaces | Aircraft, mountain and tower icing |
What Is Black Ice?
Black ice is a thin, transparent or nearly transparent coating of ice that allows dark pavement to remain visible beneath it.
Black ice can form from:
- freezing rain;
- freezing drizzle;
- refrozen meltwater;
- fog or dew freezing on cold pavement;
- wet roads freezing after a cold front;
- compacted snow becoming polished.
Black ice vs freezing rain
Freezing rain is precipitation. Black ice is a surface condition.
Where black ice forms first
- bridges and overpasses;
- shaded roads;
- ramps and curves;
- roads near rivers and lakes;
- untreated secondary roads;
- parking lots and sidewalks;
- areas where snowmelt drains across pavement.
How Ice Accretion Is Measured
Ice accretion can be described using several different measurements.
Flat ice thickness
Measures ice on a flat horizontal surface. This does not always represent the load on wires or branches.
Radial ice thickness
Measures the thickness of ice extending outward around a cylindrical object such as a wire.
Equivalent radial ice
A standardized value used to estimate the structural effect of uneven ice accumulation.
Why measurements differ
- wind makes accretion asymmetric;
- water may run off before freezing;
- surface temperature varies;
- object shape affects collection;
- precipitation rate changes freezing efficiency;
- sunlight and heat from the object may cause melting;
- different observers measure different surfaces.
Why Ice Becomes So Heavy
Ice is dense. When glaze coats the entire circumference of a wire or branch, the cross-sectional area and total mass increase rapidly.
Loading becomes especially damaging when:
- ice thickens for many hours;
- wind pushes against the enlarged ice-coated object;
- branches are already weak or diseased;
- trees retain leaves;
- wet snow later adheres to the ice;
- temperatures remain below freezing long enough to prevent shedding;
- multiple icing episodes occur before recovery.
Ice plus wind
Ice increases both weight and wind resistance. A line or branch that survives the static ice load may fail when strong wind arrives.
Ice plus snow
Snow can cling to an existing glaze layer, creating compound loading that is much greater than either hazard alone.
Why Ice Storms Cause Power Outages
Ice storms can damage several parts of the electrical grid simultaneously.
Direct line loading
Ice accumulates around conductors and communication cables, increasing their weight and causing sagging or breakage.
Tree failure
Ice-coated branches break and fall onto distribution lines.
Pole and tower loading
Utility poles and transmission structures may fail under combined ice, wind and line-tension forces.
Galloping conductors
Uneven ice accretion can change the aerodynamic shape of power lines, allowing them to oscillate strongly in wind and collide or damage hardware.
Why restoration takes so long
- roads remain impassable;
- falling branches continue after precipitation ends;
- many failures occur at once;
- replacement poles and transformers are needed;
- crews face hazardous working conditions;
- communication networks may also be damaged.
Tree and Forest Damage
Trees are highly vulnerable because branches present large collection surfaces.
Factors controlling tree damage
- ice thickness;
- wind speed;
- tree species;
- branch architecture;
- wood strength;
- existing disease or decay;
- leaf retention;
- soil saturation;
- previous storm damage.
Possible forest impacts
- broken crowns;
- snapped limbs;
- uprooted trees;
- long-term canopy loss;
- greater pest and disease exposure;
- blocked roads and trails;
- habitat changes;
- delayed power-grid restoration.
Damage may continue during thawing because ice sheds unevenly and weakened branches fail after temperatures rise.
Road, Bridge and Pedestrian Hazards
Traction loss
A very thin ice layer can drastically reduce tire grip and increase stopping distance.
Invisible transition
Drivers may leave ordinary wet pavement and encounter ice without any obvious visual warning.
Bridges and elevated roads
Bridges cool more rapidly and may freeze while nearby ground-supported roads remain wet.
Pedestrian hazards
- sidewalk falls;
- icy stairs;
- slippery parking lots;
- falling branches;
- ice falling from roofs and towers;
- blocked access for emergency services.
Why salt may struggle
Deicing chemicals may become less effective at very low temperatures or may be diluted by continuing precipitation.
Aircraft and Aviation Icing
Supercooled liquid droplets can freeze onto aircraft wings, propellers, windshields, antennas and engine components.
Why aircraft icing is dangerous
- Ice alters wing shape.
- Lift may decrease.
- Drag increases.
- Stall speed may rise.
- Control surfaces may become restricted.
- Propeller and engine performance may be affected.
- Sensors and antennas may ice over.
Freezing rain and large droplets
Large supercooled droplets can flow beyond protected leading edges before freezing, creating difficult-to-control ice accumulation.
Ground operations
Ice storms also disrupt airports through:
- runway and taxiway icing;
- aircraft deicing delays;
- gate and ramp hazards;
- equipment icing;
- crew and passenger disruption.
Buildings, Towers and Infrastructure
Communication towers
Towers, antennas and cables collect ice and experience greater weight and wind loading.
Rail systems
- switches freeze;
- overhead electrical systems accumulate ice;
- platforms become dangerous;
- trees fall across tracks;
- braking performance declines.
Buildings
- gutters and drains freeze;
- roof edges accumulate ice;
- falling ice threatens pedestrians;
- doors and equipment freeze shut;
- backup generators become inaccessible;
- heating demand rises during power loss.
Agriculture
- orchard branches break;
- greenhouses suffer structural loading;
- livestock areas become inaccessible;
- water systems freeze;
- feed and fuel deliveries are interrupted.
Cold-Air Damming and Appalachian Ice Storms
Cold-air damming occurs when dense cold air becomes trapped against the eastern side of a mountain range while warmer air moves above it.
This setup is especially important east of the Appalachian Mountains.
How the process works
- High pressure supplies cold, dense air near the surface.
- The mountains inhibit westward movement of that air.
- Warm, moist air flows above the shallow cold layer.
- Snow melts inside the warm layer.
- The rain becomes supercooled in the trapped surface cold.
- Freezing rain accumulates across the Piedmont and adjacent valleys.
Why cold air can persist
- Cold air is dense and shallow.
- Terrain restricts its movement.
- Evaporative cooling can reinforce it.
- Surface winds may maintain cold-air supply.
- Numerical models may erode it too quickly.
Ice Storms Inside Major Winter Cyclones
Freezing rain often forms within the transition zone of a large winter storm.
A single cyclone may produce:
- heavy snow on its colder side;
- sleet near the melting boundary;
- freezing rain where warm air overruns shallow surface cold;
- ordinary rain farther into the warm sector;
- strong wind and coastal flooding elsewhere.
Nor’easters
Nor’easters can produce freezing rain inland or near the rain–snow transition zone, while the coast receives rain and farther inland receives snow.
Bomb cyclones
Rapidly intensifying cyclones can strengthen warm-air transport aloft while shallow cold remains near the surface.
Mixed-precipitation storms
The most disruptive events may alternate between snow, sleet and freezing rain as atmospheric layers change.
Where Ice Storms Happen Most Often
Ice storms favor transition zones where shallow surface cold can survive beneath warmer, moisture-rich air.
| Region | Typical setup | Primary hazards |
|---|---|---|
| Central and Eastern United States | Warm moist air overruns shallow continental or Arctic air | Road icing, tree damage and major outages |
| Appalachian Piedmont | Cold-air damming east of the mountains | Long-duration glaze and difficult forecasts |
| Southern Canada | Strong temperature contrasts near winter storm tracks | Widespread ice accretion and transmission damage |
| New England and the St. Lawrence Valley | Warm Atlantic air overruns entrenched surface cold | Freezing rain, sleet, outages and transport disruption |
| Northern and Central Europe | Atlantic warmth crossing cold continental boundary layers | Black ice, freezing rain and railway disruption |
| Eastern Europe and Russia | Warm advection above cold continental air | Freezing rain, glazed roads and infrastructure icing |
| East Asia | Cold continental air beneath warmer moist storm flow | Ice accretion, road shutdowns and power-grid stress |
| Mountain valleys worldwide | Dense cold air trapped beneath warmer air aloft | Persistent local freezing rain and black ice |
Major Historical Ice-Storm Patterns
Keep this section selective and pattern-based rather than creating an endless chronological event log.
Multi-day regional ice storms
These occur when warm moist flow repeatedly overruns entrenched surface cold, allowing glaze to accumulate through several precipitation waves.
Cold-air-damming ice storms
Shallow cold remains trapped against mountains while warmer air persists aloft.
Transmission-grid disasters
Heavy ice, wind and tree failure damage both local distribution systems and high-voltage infrastructure.
Freezing-rain road disasters
Thin glaze or freezing drizzle produces widespread crashes despite relatively small precipitation totals.
Compound snow–sleet–ice storms
Snow creates initial accumulation, sleet adds dense weight and freezing rain seals the surface beneath glaze.
How Is Freezing Rain Forecast?
Forecasting freezing rain requires a detailed understanding of the vertical atmosphere and the temperature of exposed surfaces.
Forecasters examine:
- temperature from cloud level to ground;
- depth and warmth of the melting layer;
- depth and temperature of surface cold air;
- wet-bulb temperature;
- surface and road temperature;
- precipitation rate and duration;
- cold-air damming strength;
- wind direction and terrain;
- expected ice accretion;
- probability of sleet mixing;
- timing of surface warming.
Forecast tools
- surface weather stations;
- road-weather sensors;
- weather balloons;
- aircraft observations;
- Doppler radar;
- satellite data;
- high-resolution numerical models;
- ensemble forecasts;
- ice-accretion models;
- local terrain and climatology.
Why Freezing-Rain Forecasts Change
Small temperature errors
A change of only 1–2°C in one atmospheric layer can shift precipitation among snow, sleet, freezing rain and rain.
Shallow cold air
Surface cold may be only a few hundred meters deep and can be poorly resolved by coarse models.
Cold-air damming
Models may remove trapped cold air too quickly, causing freezing rain to persist longer than forecast.
Road temperature
Air temperature may rise above freezing while bridges, shaded roads or frozen ground remain cold enough for ice.
Precipitation intensity
Heavy precipitation may cool the surface through melting and evaporation, or provide enough liquid to overcome freezing efficiency through runoff.
Sleet mixing
Slightly deeper surface cold can cause more sleet, reducing glaze but increasing dense surface accumulation.
Latent heat release
Freezing releases heat, which can gradually warm exposed surfaces toward 0°C and alter accretion efficiency.
How Does Freezing Rain Appear on Radar?
Weather radar detects precipitation particles aloft but does not directly measure whether a road surface is freezing.
Freezing rain may appear similar to ordinary rain on reflectivity imagery.
Dual-polarization radar can help identify:
- melting snow aloft;
- the bright band associated with melting precipitation;
- transitions among snow, sleet and rain;
- mixed precipitation zones.
Radar limitations
- It may overshoot shallow freezing drizzle.
- It cannot determine every local road temperature.
- Precipitation type can change below the radar beam.
- Terrain can block or distort the beam.
- Very light drizzle may produce weak returns.
Surface Observations and Weather Balloons
Weather balloons
Balloon soundings reveal the vertical temperature and humidity profile and help identify:
- the cold cloud layer;
- the warm nose;
- the depth of surface cold;
- moist and dry layers;
- wind changes with height.
Surface stations
Stations report:
- air temperature;
- dew point;
- wind;
- precipitation type;
- visibility;
- sometimes ice accretion.
Road-weather systems
Road sensors help determine whether pavement is:
- dry;
- wet;
- below freezing;
- chemically treated;
- already coated in ice.
Reports from trained observers, airports, utility crews and transportation agencies remain important because glaze can vary sharply over short distances.
Ice-Storm Warnings and Advisories
Terminology and thresholds vary by country and forecast office.
Possible alerts include:
- ice storm warning;
- freezing rain warning;
- winter storm warning;
- winter weather advisory;
- freezing drizzle advisory;
- black-ice warning or road advisory;
- airport icing advisory;
- special weather statement;
- travel emergency.
Watch vs warning
A watch generally indicates that significant icing is possible. A warning indicates that dangerous icing is expected, imminent or occurring.
Why thresholds vary
- local infrastructure differs;
- tree species and vegetation differ;
- utility-grid design differs;
- regional ice-storm frequency differs;
- transportation systems have different tolerances.
After-Storm Dangers
The danger does not end when freezing rain stops.
Delayed tree failure
Ice-loaded branches may continue snapping as wind changes or temperatures rise.
Falling ice
Ice can fall from:
- roofs;
- trees;
- bridges;
- towers;
- power lines;
- wind turbines;
- aircraft and vehicles.
Refreezing
Partial daytime melting may freeze again after sunset.
Carbon-monoxide danger
Long outages increase generator and alternative-heating use, raising the risk of carbon-monoxide poisoning.
Utility hazards
- downed lines may remain energized;
- damaged trees may contact wires;
- restoration traffic may be heavy;
- unstable poles may fail later.
Ice-Storm Safety
Before an ice storm
- Monitor official forecasts and warnings.
- Charge phones, batteries and emergency power supplies.
- Prepare for a prolonged outage.
- Store food, water and necessary medication.
- Fuel vehicles before roads become icy.
- Check carbon-monoxide and smoke detectors.
- Secure safe generator placement.
- Prepare pets and livestock.
During freezing rain
- Avoid driving unless absolutely necessary.
- Assume untreated roads and bridges are icy.
- Stay away from trees and power lines.
- Do not park beneath large branches.
- Remain indoors when heavy accretion is occurring.
- Do not use generators or grills inside buildings.
- Report downed lines to the responsible utility.
If driving cannot be avoided
- Reduce speed well before reaching bridges and curves.
- Increase following distance.
- Avoid sudden acceleration, steering and braking.
- Do not use cruise control.
- Carry emergency supplies.
- Follow official road closures.
During a power outage
- Use flashlights instead of candles where possible.
- Keep generators outdoors and far from windows.
- Prevent frozen pipes where safe.
- Conserve phone battery.
- Check vulnerable neighbors.
- Move to an official warming center if indoor temperature becomes unsafe.
After the storm
- Beware of falling branches and ice.
- Do not approach downed electrical wires.
- Use traction aids on icy walkways.
- Clear furnace and vehicle exhaust vents.
- Monitor refreezing overnight.
- Photograph damage only from a safe location.
Climate and Future Freezing-Rain Risk
Freezing rain occurs near a narrow thermal boundary, making future changes highly regional.
Possible increases in some transition zones
Some locations may experience more winter precipitation falling through warm layers while shallow surface cold remains available.
Possible decreases in warmer regions
Where surface temperatures increasingly remain above freezing, freezing rain may shift toward ordinary rain.
Snow-to-ice transitions
Some storms that historically produced snow may produce more sleet or freezing rain during marginal-temperature events.
Moisture availability
A warmer atmosphere can hold more water vapor, but damaging ice still requires subfreezing exposed surfaces.
Storm-track and cold-air changes
Future risk depends on:
- storm tracks;
- frequency of shallow cold-air pools;
- mountain cold-air damming;
- surface warming;
- precipitation intensity;
- regional circulation changes.
Ice-Storm Myths and Misconceptions
| Myth | Reality |
|---|---|
| Freezing rain is frozen before it lands. | It reaches the ground as liquid water and freezes after impact. |
| Sleet and freezing rain are the same. | Sleet freezes before reaching the surface; freezing rain freezes on contact. |
| Black ice is a special type of rain. | Black ice is a thin surface coating that can form through several processes. |
| A thin ice layer is harmless. | Even light glaze can cause severe road and pedestrian hazards. |
| Ice storms require extremely cold air. | They often occur near freezing with warm air aloft and shallow surface cold. |
| If air temperature reaches 1°C, all ice melts immediately. | Roads, bridges, trees and other surfaces may remain below freezing. |
| Ice storms are less damaging than snowstorms. | They can cause greater power-grid and tree damage with much less precipitation. |
| Four-wheel drive makes freezing-rain travel safe. | It does not restore braking or steering traction. |
| Radar always detects freezing drizzle. | Shallow drizzle may produce weak returns or occur beneath the radar beam. |
| The danger ends when precipitation stops. | Falling branches, downed wires, refreezing and falling ice can continue for hours or days. |
Legacy Article and Redirect Classification
Redirect a legacy article to this pillar when the main scientific mechanism or impact is freezing rain and damaging ice accretion.
Redirect here when the main story is:
- an ice storm;
- freezing rain;
- freezing drizzle;
- glaze ice;
- black ice caused by freezing rain or refreezing;
- ice-covered roads and bridges;
- tree failure caused by ice accretion;
- power outages caused by ice loading;
- cold-air damming and freezing rain;
- sleet vs freezing rain;
- aircraft icing during freezing rain;
- transmission-line or tower icing;
- a mixed winter storm where damaging ice is the dominant impact.
Redirect elsewhere when the dominant subject is:
| Dominant subject | Best destination |
|---|---|
| Heavy snow, whiteouts, drifting or ground blizzards | Blizzards and Major Snowstorms |
| Cold air crossing open water and producing narrow snow bands | Lake-Effect Snow |
| East Coast cyclone track, coastal flooding or nor’easter identity | Nor’easters |
| Explosive cyclogenesis or rapid pressure deepening | Bomb Cyclones |
| Extreme cold, Arctic air or wind-chill impacts | Arctic Outbreaks and Cold Snaps |
| Stratospheric polar-vortex disruption | Polar Vortex Explained |
| Rime formations, frost flowers or unusual natural ice structures | Strange Ice and Snow Phenomena |
Sources and Editorial Methodology
Freezing-rain classifications, ice-accretion totals and warning criteria should be checked against the responsible meteorological authority.
Preferred primary sources
-
NOAA National Weather Service: Ice and Frost
-
NOAA National Severe Storms Laboratory: Winter Precipitation Types
-
NOAA National Weather Service forecasts, warnings and storm reports
- Environment and Climate Change Canada warnings and storm analyses.
- National meteorological services for regional freezing-rain events.
- Official road-weather and aviation observations.
- Utility-company damage and restoration reports.
- Peer-reviewed research on freezing rain and ice accretion.
StrangeSounds editorial rules
- Distinguish freezing rain from sleet.
- Distinguish glaze ice from black ice.
- Distinguish freezing rain from freezing drizzle.
- Use the complete vertical temperature profile.
- Do not infer surface icing from radar alone.
- State whether ice totals are measured, estimated or forecast.
- Identify the measurement type where available.
- Do not equate liquid precipitation totals with radial ice thickness.
- Use official outage and damage information.
- Redirect events according to their dominant meteorological mechanism.
Frequently Asked Questions About Ice Storms and Freezing Rain
What is an ice storm?
An ice storm is a winter-weather event in which freezing rain accumulates on exposed surfaces and produces significant or damaging glaze ice.
What is freezing rain?
Freezing rain is liquid precipitation that becomes supercooled in shallow surface cold and freezes when it strikes a subfreezing surface.
How does freezing rain form?
Snow melts in a warm layer aloft, then the liquid drops enter a shallow subfreezing layer and freeze only after reaching cold surfaces.
What is the warm nose?
The warm nose is a layer of above-freezing air aloft that melts falling snow into rain.
What does supercooled water mean?
Supercooled water remains liquid below 0°C and freezes rapidly after contacting a suitable surface or ice nucleus.
What is the difference between freezing rain and sleet?
Sleet refreezes into ice pellets before reaching the ground. Freezing rain remains liquid until it freezes after impact.
What is the difference between freezing rain and freezing drizzle?
Both freeze on contact, but freezing drizzle consists of smaller droplets and often develops in shallow low clouds.
What is glaze ice?
Glaze is a smooth, dense and often transparent ice coating formed when supercooled rain or drizzle freezes on exposed objects.
What is black ice?
Black ice is a thin, nearly transparent surface coating that allows dark pavement to remain visible beneath it.
Is black ice the same as freezing rain?
No. Freezing rain is precipitation. Black ice is a surface condition that may result from freezing rain, freezing drizzle, refreezing or frozen fog and dew.
Why do bridges freeze before roads?
Bridges lose heat from both above and below, while roads receive some heat from the ground beneath them.
Why are ice storms so dangerous?
Ice storms create extremely slippery surfaces while loading trees, wires, poles and infrastructure with dense ice.
Why do ice storms cause power outages?
Ice adds weight to trees and power lines, while wind increases stress and can break branches, conductors, poles and transmission structures.
Can freezing rain occur when air temperature is above 0°C?
Yes. Exposed surfaces may remain below freezing even when the measured air temperature has risen slightly above 0°C.
Can an ice storm happen without snow?
Yes. The principal hazard is freezing rain and glaze ice, and little or no snow may fall at the surface.
What is cold-air damming?
Cold-air damming occurs when dense shallow cold air becomes trapped against a mountain range beneath warmer air aloft.
Why are freezing-rain forecasts difficult?
Small temperature errors in thin atmospheric layers can change precipitation from snow to sleet, freezing rain or ordinary rain.
Can freezing drizzle be detected by radar?
Sometimes poorly. Shallow freezing drizzle may produce weak echoes or occur below the radar beam.
How is ice accumulation measured?
Ice can be measured as flat thickness, radial thickness or equivalent radial ice, depending on the observing method and object.
Does one inch of freezing rain create one inch of ice?
No. Runoff, wind, surface temperature, object shape and freezing efficiency affect the final ice thickness.
Can ice storms damage aircraft?
Yes. Supercooled droplets can freeze on aircraft surfaces, alter aerodynamics, increase drag and reduce lift.
Can a nor’easter produce an ice storm?
Yes. Inland or transition-zone areas may receive freezing rain while other parts of the same nor’easter receive snow or rain.
Can a bomb cyclone produce freezing rain?
Yes. Rapidly intensifying cyclones can transport warm air above shallow surface cold and create mixed winter precipitation.
Where do ice storms happen most often?
They are common in transition zones where warm moist air overrides shallow surface cold, including parts of central and eastern North America, southern Canada, Europe and East Asia.
Does climate change mean more ice storms?
Not everywhere. Risk may shift geographically as some snow events become freezing rain while warmer areas increasingly receive ordinary rain.
What should you do during freezing rain?
Avoid unnecessary travel, stay away from ice-loaded trees and power lines, prepare for outages and use generators only outdoors.
Where should freezing-rain articles redirect?
Redirect them here when freezing rain, glaze ice, black ice, ice accretion or ice-related power damage is the main subject.
Where should snowstorm articles redirect?
Redirect heavy-snow, whiteout, blowing-snow and ground-blizzard articles to Blizzards and Major Snowstorms Explained.
