What is the difference between sleet and hail?
Precipitation has many forms and can occur under a wide range of circumstances, making weather events both fascinating and puzzling.
Sleet and hail are two such phenomena that are often mixed up because of their superficial similarities.
But, there are some fundamental differences you need to understand.
To effectively describe weather occurrences, estimate their potential repercussions, and take necessary safety precautions, it is important to know, “What is the difference between hail and sleet?”
Small ice pellets, or sleet, occur when raindrops freeze, whereas hail forms when raindrops become supercooled and grow into larger, layered ice balls, or hailstorms.
Various Types of Precipitation
Precipitation is any water that falls from the atmosphere to the ground.
The water can be solid, like hail, liquid like rain or fall as sleet which is somewhere in between.
Precipitation is a vital stage of the Earth’s hydrological cycle, replenishing and distributing fresh water across the planet.
But, it is crucial to understand the differences in weather occurrences to understand their impact on the environment.
Fact: Freezing rain, which is sometimes mistaken for sleet, actually results from droplets freezing upon contact with cold surfaces, forming ice coats rather than pellets.
Getting Familiar with Hail
Hail forms in the updrafts of thunderstorms when water droplets are carried up the air current into the extreme cold of the atmosphere where they freeze.
They grow as they rise, colliding to form balls of ice. The ice can be cloudy because air is in it, or clear because compression has forced it out.
When the hailstone gets too heavy for the updraft to support or its force weakens, it falls down to earth.
Getting Familiar with Sleet
Sleet is solid precipitation but it has started to melt on its way down as it passes through a warm layer of air.
It arrives on the ground level as a mixture of rain and snow crystals.
The sleety drops can re-freeze if they meet air that is cold enough, in which case each drop will bounce as it hits the ground.
Although sleet is often slushy, it collects like snow when conditions are right.
Fact: Strong thunderstorms, known as supercells, are ideal for the formation of hail because of the updrafts they generate, which keep the hailstones suspended in the cloud.
What is the Difference between Sleet and Hail?
Hail and sleet are forms of frozen precipitation that occur at different times of the year.
Sleet is a winter precipitation whereas hail events happen in summer.
They both cause inconvenience, for example sleet is slippery but hail causes significant damage taking lives as the hailstones are getting bigger.
Key Differences Between Sleet and Hail
Hail and sleet form in different conditions and have different characteristics.
Apart from the amount of damage they cause, one key difference is the time of year in which they occur.
Hail is a product of summer weather but sleet, which is partially frozen rain, is a winter weather event.
Hail begins its life at the bottom of storm clouds whereas sleet forms in a cloud that has warm air under it.
Atmospheric Conditions and Weather Patterns
Whether or not hail will form is difficult to predict.
But its likelihood increases when the weather is hot and humid and towering cumulonimbus clouds typical of summer thunderstorms form.
Water vapor condenses at the bottom of the cloud but instead of falling, it is carried aloft in an updraft of warm air.
When temperatures in a cloud are at or below 0°C (32°F) water vapor freezes into ice.
It sticks together to make snow crystals.
It takes just a slight difference in temperature for snow to be sleet, and sleet to be rain, which makes accurately forecasting sleet problematic.
An Important Consideration
Sleet occurs in winter when temperatures are low but only when the snowflakes fall through a layer of air with a temperature above zero.
It will refreeze if the temperature falls again.
The snowflake may go through melting and refreezing cycles, changing its appearance, texture and size.
Fact: The largest ever recorded American hailstone was an 8-inch diameter, 1.94-pound monster that landed in Vivian, South Dakota in 2010.
Formation Processes
At altitude, especially in colder temperatures, almost all precipitation starts as snow.
The cloud snow stays suspended for as long as the cloud can support its weight and the temperature stays below freezing.
Forming at the base of a cloud, hail is an exception.
The water drops that form hail freeze as they are forced up the thundercloud’s updraft to the extreme cold at the top of the cloud.
As they ascend, contained by the updraft, a raging current of warm air, the drops dump into each other and coalesce as they collide.
Smaller drops that are already solid ice pellets are coated in a film of cold water which freezes so they grow.
Eventually, high up they get too heavy for the weakening updraft to hold and fall to the ground as hailstones.
Sleet however, is cloud snow that becomes too heavy for the cloud and falls.
Fact: Each year in the United States, hail damages about $1 billion worth of crops, vehicles, and property.
Appearance, Texture and Size
In weather forecasting, hail is either large or small, less than 5mm.
Because of the dumping around in the updraft, hailstones collect various compounds and so are aggregates.
As such, it can be classified into several types, each with their own characteristics.
For example:
- Ice prisms, also called diamond dust, are tiny unbranched ice crystals.
- Snow grains are rice-sized, hard and flat
- Graupel or tapioca hail is soft and mostly conical in shape
Sleet forms in conditions like those that produce freezing rain.
They both begin their descent as snowflakes and pass frozen through at least one layer of warmer air to melt.
Sleet is semi-frozen water and slushy; not supercooled like freezing rain. It is small, less than 5mm and light enough to make a slow descent through colder air.
If the layer is deep and cold below zero the partially frozen liquid will become solid.
Associated Hazards and Impact
Temperatures change between cloud and ground sometimes abruptly, so some precipitation falls locally. Hail and sleet fall into this category.
Given that sleet creates hazardous driving conditions, and hail kills livestock, forecasters can only talk about the likelihood of an event.
It is impossible to predict exactly when and where either could happen.
Climate change researchers predict higher temperatures and more rain, particularly the fierce summer superstorms that have produced huge hailstones.
An Important Thing to Consider
Our climate will be warmer. There is already less snowfall and not enough to replenish lost mountain snow and polar ice.
Without snow’s protection as an insulator and reflector, surface temperatures will rise.
Snow will have less chance to make it to the ground frozen as temperatures rise in the layers of the atmosphere.
In the future, it seems likely that with global temperature changes there will be more sleet, along with more giant hail.
Differences in Meteorological Tools Used to Monitor Hail and Sleet
Meteorologists assume all hailstones to be spherical. That way they can describe the size of hail in a standardized way.
However, because atmospheric temperatures and the depth of the cold layers fluctuate, there is an infinite number of possible hailstone sizes, the largest so far is almost 2 lbs.
Weather reporters wisely fall back on comparing hailstone sizes to known objects, like peas, coins and fruit.
Monitoring weather systems for signs of conditions likely to produce sleet is a more technologically advanced affair.
Multiple satellites track and monitor winter storms, collecting real time data on all sorts of things, particularly the temperatures.
Fact: Depending on the storm's intensity and the surrounding weather, the duration of a hailstorm can range from a few minutes to well over an hour.
Takeaway
What is the difference between sleet and hail? When raindrops encounter a layer of sub-freezing air, they freeze and eventually form tiny, translucent ice pellets known as sleet.
In contrast, hail consists of larger, layered ice balls created within powerful thunderstorms as supercooled water droplets strike with ice particles and solidify.
So, sleet and hail are different in their physical features, how they form in the atmosphere, and how heavy they can become.
