How Does a Hail Storm Form? Storm Safety & Lifecycle Guide
A winter squall can move across the Sunshine Coast with little warning, bringing thunder, gusty winds and small hail even though severe storms usually peak in warmer months. That sudden burst of ice raises a familiar question: how does a hail storm form? This guide explains the hail formation process, walking you through the key atmospheric triggers, how a hailstone grows inside the cloud, and explains how to read BOM warnings and prepare before severe hail reaches your area.
How Does a Hail Storm Form? The Life Cycle of a Hailstone
How does hail form inside a thunderstorm? Hailstones do not develop simply because falling raindrops freeze. They grow through a multi-stage process inside tall convective clouds.
1. Thunderstorm Development and Strong Updrafts
The hail formation process begins with a tall thunderstorm, usually a cumulonimbus cloud. For that storm to develop, warm moist air near the surface must rise into cooler air above.
Three ingredients matter most at this stage:
Moist air provides the water needed for cloud, rain and hail formation.
Unstable air allows that warm air to keep rising rather than sink back down.
A lifting trigger starts the upward movement.
That lift can come from surface heating, a cold front, a low-pressure trough, a sea-breeze boundary or elevated terrain. Together, these conditions help explain what causes a hail storm. As the air rises and cools, the cloud grows taller and a strong updraft begins to form inside it.
2. The Formation of a Hail Embryo
Higher inside the thunderstorm, some droplets remain liquid even though the surrounding temperature has dropped below 0°C. These are known as supercooled water droplets.
A hail embryo forms when one of these droplets freezes onto a small ice particle. This starting particle may be a frozen droplet or a soft ice pellet such as graupel. Once the first frozen core appears, it becomes the base on which the hailstone can continue to grow.
At this point, the embryo is still very small. To become a true hailstone, it must remain inside the storm long enough to collect more frozen water.
3. Hailstone Growth Inside the Storm
Once the hail embryo moves through a part of the storm rich in supercooled water, more droplets strike its surface and freeze. Each collision adds another layer of ice.
This is the central growth stage of hail development. The updraft keeps the hailstone suspended inside the cloud, and as long as it stays in the cold moisture-rich zone, it continues adding ice.
The process usually works like this:
The updraft keeps the embryo inside the storm.
Supercooled droplets collide with the ice core.
The droplets freeze onto the surface.
The hailstone gradually becomes heavier.
4. The Final Descent to the Ground
A hailstone eventually starts falling when it can no longer remain supported inside the storm. This may happen because it becomes too heavy, because the updraft weakens or because it moves out of the main rising air current.
Once it begins to descend, it passes through warmer air below the cloud. Some melting may occur on the way down, but if enough ice remains, it reaches the ground as hail.
.PNG)
Why Hailstones Differ in Size, Shape and Damage?
Two homes in the same storm can experience very different results. One street may receive small hail that collects in gardens, while another sees larger stones dent cars or crack roof materials. The final outcome depends on how the hail grows inside the cloud, how much it melts during the fall and what it strikes at ground level.
Hailstone Size: Storm Strength and Time Inside the Cloud
Larger hail needs suitable conditions to continue for long enough:
Strong updrafts support heavier stones and delay their descent.
Supercooled water supplies the droplets that freeze onto the surface.
Long-lived storms keep the growth zone active for longer.
All three conditions matter. A strong updraft with limited liquid water may support ice without adding much new growth. Hail also stops growing once it leaves the moisture-rich part of the storm.
This helps explain why short thunderstorms often bring small hail, while long-lived severe storms carry a greater risk of large or giant hail.
Hailstone Layers and Shape: Temperature and Moisture Inside the Storm
Changing conditions inside the cloud affect the appearance of the hailstone.
Freezing Conditions | Resulting Ice |
Droplets freeze quickly and trap air bubbles | Cloudy or white layers |
Water spreads before freezing | Clearer, denser layers |
A hailstone can develop alternating layers as it passes through areas with different temperatures and moisture levels. Uneven freezing and rotation also create bumps, ridges and irregular edges.
These shapes can influence how a stone falls and which part hits a windscreen, roof tile or solar panel first.
Hail Damage: Melting, Wind and What Hail Strikes
Hail begins to melt below the freezing level. A deep layer of warm air can reduce its size before impact, while larger stones have a better chance of reaching the ground intact.
Strong winds also change the damage pattern. Wind-driven hail can strike:
Vehicles and glazing
Roofs, cladding and solar panels
Crops and exposed plants
Damage also depends on the condition of the exposed material. Older roof tiles may crack more easily, and a long period of hail can cause wider cumulative damage across a property.
When and Where Do Hailstorms Form in Australia?
Hailstorms can develop across most parts of Australia, but their timing, size and frequency vary with local climate and storm conditions.
Australia’s Main Hailstorm Season
Large hail occurs most often during spring and early summer, when warmer surface air supports strong updrafts and cold air remains available higher in the atmosphere. Australia’s wider severe thunderstorm season generally runs from September to March, although the peak period differs between regions.
Spring to early summer: Increasing surface warmth and moisture support rapidly growing thunderstorms. Cold upper-level air helps water and ice remain within the hail growth zone.
Mid to late summer: Severe hail remains possible, particularly around Sydney and other parts of eastern Australia. Local moisture, troughs, wind shear and upper-level temperatures determine whether a storm produces damaging hail.
Cooler months: Southern coastal areas can receive small hail with cold fronts and winter showers, even without the intense surface heating associated with warm-season severe storms.
Primary Hail Regions
Eastern Australia contains the country’s most prominent hail-prone corridor, especially from south-east Queensland through northern and eastern New South Wales. Other states also experience hail, but the season and typical storm type vary.
Region | Higher-Risk Period | Typical Pattern | Main Drivers |
South-east Queensland and northern NSW | Spring to early summer; Brisbane often peaks in December | Australia’s main damaging-hail corridor, with occasional giant hail | Moist coastal air, inland troughs, sea breezes and the Great Dividing Range |
Sydney, Illawarra and Hunter | November to March | Damaging hail across coastal suburbs and nearby inland areas | Sea-breeze boundaries, troughs, unstable air and elevated terrain |
Inland NSW and the ACT | Mainly spring and summer | Localised severe storms may produce large hail | Daytime heating, troughs, cold air aloft and wind shear |
Victoria, South Australia and south-west WA | Small hail in cooler months; damaging hail also possible in warmer months | Winter fronts often bring small hail; stronger thunderstorms can bring larger stones | Cold fronts, unstable air and passing troughs |
Why Winter Hail Happens and Tropical Hail Often Melts
The freezing level helps explain why southern winter showers can produce small hail at the surface, while many tropical thunderstorms contain ice that melts before reaching the ground.
Winter Hail in Southern Australia
Strong cold fronts, including the systems often described as a polar blast, can bring much colder air across Victoria, South Australia, Tasmania and south-west Western Australia during winter. This lowers the freezing level and shortens the distance that falling ice must travel through warmer air.
Small ice particles have less time to melt before reaching the surface.
Winter updrafts usually remain weaker than the updrafts in severe spring and summer storms.
The hail commonly reaches the ground as small pellets instead of large, damaging stones.
This is why a cold winter shower can cover lawns or roads with small hail even when the storm lacks the strength needed to produce giant hail.
Tropical Hail in Northern Australia
Northern Australia experiences frequent thunderstorms, but large hail remains uncommon at ground level. The tropical freezing level often sits around 5 to 6 kilometres above the surface, leaving a deep layer of warm air below the hail growth zone.
Ice forms high inside many tropical thunderstorms.
Falling hail must travel through several kilometres of warm, humid air.
Much of the ice melts into rain before reaching the surface.
Small hail can still occur, and isolated tropical storms can produce larger stones when strong updrafts support enough growth. However, damaging hail reaches the ground less often around Darwin, Cairns and the Kimberley than along Australia’s subtropical east coast.
Hailstorm Warnings, Safety and Property Checks
When severe weather threatens, staying informed and taking prompt safety measures reduces property damage and personal risk. Monitoring official updates helps you prepare before ice begins to fall.
Understanding BOM Hailstorm Warnings
Check the hail size mentioned in the warning: Large hail means stones at least 2 cm across. Giant hail means stones at least 5 cm across and signals a much higher risk of serious injury and major property damage.
Find your location on the warning map: A regional warning can cover a broad area, so not every suburb will receive hail. Detailed warnings may show the storm’s current position and projected path.
Check the issue time and storm direction: Severe cells can strengthen, weaken or change direction quickly. Review the latest update instead of relying on an earlier forecast.
Follow the storm on BOM rain radar: Open the BOM rain radar and weather maps and select your local area. Watch several frames to check the storm’s recent direction and movement, but continue following the official warning because radar observations do not show exactly what will reach the ground.
Match your response to the warning level: If large hail is approaching, move vehicles under solid cover and secure loose items while conditions remain safe. If BOM mentions giant hail or a very dangerous thunderstorm, stop outdoor preparations and shelter indoors away from windows and skylights.
What to Do Before and During a Hailstorm
Once a BOM warning shows that severe hail may affect your area, follow basic hail storm safety steps while conditions remain safe and move indoors before the storm arrives.
Pre-Storm Safety Actions (When Safe and Time Permits)
Protect Vehicles: Drive or park vehicles inside a secure garage or carport. If undercover parking is unavailable, thick car covers, heavy blankets, or tarpaulins can offer secondary protection against minor hail.
Secure Loose Outdoor Items: Store garden furniture, potted plants, rubbish bins, and trade tools inside a shed or garage to prevent wind damage.
Shelter Pets: Bring domestic animals indoors before precipitation starts, as loud hail impacts can startle livestock and pets.
Secure the Building: Close all windows, external doors, and curtains. Stay away from glass windows, skylights, and glass sliding doors.
Charge Essential Devices and Backup Power: Severe storms can damage local powerlines and interrupt electricity supply. Charge phones, power banks and portable power stations before conditions deteriorate, then decide which devices need priority during an outage. Refrigeration, a modem, lighting and phone charging will usually matter more than non-essential household appliances.
The EcoFlow DELTA 2 Max Portable Power Station offers flexible backup for short or overnight disruptions. Fast AC charging helps you prepare when a storm warning arrives, while expandable capacity gives you more room if restoration takes longer than expected.
For larger residential power requirements, the EcoFlow DELTA Pro 3 Portable Power Station delivers robust output capable of running heavy-duty household appliances during prolonged power disruptions. Featuring fast UPS switchover capability, it seamlessly maintains continuous power to sensitive electronics and critical equipment the moment the main grid disconnects.
Safety During the Storm
Remain Indoors: Do not step outside to move vehicles or protect outdoor items once hail begins to fall.
Driving Safety: Avoid driving into the core of a thunderstorm. If caught on the road, pull over safely away from trees, powerlines, and low-lying flood zones, and stay inside the vehicle with hazard lights on.
Checking Damage and Starting an Insurance Claim
Once the warning has passed and conditions are safe, check your property carefully before arranging repairs.
Inspection Area | Specific Items to Check | Safety Caution |
External Hazards | Fallen powerlines, loose electrical connections, downed tree branches | Stay at least 8 metres away from fallen powerlines; report them to energy providers. |
Roof & Drainage | Broken roof tiles, cracked tin sheets, dented gutters, blocked downpipes | Inspect from ground level using binoculars; avoid walking on wet or structurally compromised roofs. |
Windows & Interior | Shattered skylights, cracked glass doors, ceiling water marks near switchboards | Do not touch a wet or damaged switchboard or attempt to restore power. Keep clear and contact a licensed electrician. |
Solar Infrastructure | Visible glass fractures or frame damage on rooftop solar panels | Treat all solar components as live; do not touch cracked panels. |
Vehicles | Windscreen cracks, dented bonnets, broken side mirrors | Photograph damage from multiple angles before moving the vehicle. |
Steps for Insurance Claims
Document Everything: Capture clear photos and videos of structural damage, flooded rooms, dented vehicles, and ruined possessions before clearing debris.
Keep Receipts: Retain itemised tax receipts for emergency repairs, temporary tarping services, vehicle towing, or emergency accommodation.
Contact Your Insurer: File your claim online or via phone as early as possible. Confirm approved repair procedures and schedule an assessor site visit before authorising major permanent repairs.
Conclusion
So, how does a hail storm form? It begins when a strong updraft carries a small ice embryo through supercooled water inside a tall storm cloud. While meteorologists cannot stop ice from forming inside storm clouds, tracking live BOM radar updates and taking early safety steps reduce property loss. Parking vehicles undercover, securing outdoor items, and preparing emergency power backup help your household stay safer and connected when severe convective storms sweep across Australia.
FAQs
Are hailstones painful?
Yes. Even small hail can sting exposed skin, while larger stones may cause bruising or more serious injuries. Strong winds can increase the impact, so move indoors as soon as hail begins and stay away from windows and skylights.
Can hail form without a thunderstorm?
Small hail can form in tall convective shower clouds, so it may reach the ground even when you do not notice obvious thunder or lightning. This sometimes happens behind winter cold fronts in southern Australia, where cold air lowers the freezing level and short, vigorous showers produce small hail. Large and damaging hail, however, generally needs the stronger, longer-lasting updrafts found inside thunderstorms.
What's the worst hail ever recorded in Australia?
The answer depends on whether you mean the largest hailstone or the most destructive storm. Australia’s largest confirmed hailstone measured 16 cm at Yalboroo, Queensland, on 19 October 2021. The 1999 Sydney hailstorm was one of the country’s most damaging, affecting more than 20,000 homes and around 70,000 vehicles and causing over A$1.7 billion in insured losses.