What's the Difference Between Snow, Sleet, and Freezing Rain?
As we make it through the winter, meteorologists in many parts of the country are predicting all sorts of cold-weather precipitation: snow, sleet, freezing rain. But what's the difference?
All precipitation falls through the atmosphere on its way to the Earth's surface. Imagine a drop or flake falling through a long tube that contains the air between the clouds and the Earth.
The air inside the imaginary tube is the atmosphere. Differences in temperatures in different parts of the atmosphere account for the differences we see between snow, sleet, and freezing rain.
The liquid precipitation that falls to Earth's surface is rain. Rain can begin as snow, but by the time it reaches the Earth's surface, it has melted because the temperature closer to Earth is warmer.
If you've ever thought it strange that it's raining when the temperature outside is below freezing, it's probably because the temperature higher up in the atmosphere is still above freezing.
Snow forms in clouds at temperatures below freezing. As snow falls through the atmosphere, the air remains at least 32° F or colder. In order for a snowflake to reach Earth, it must remain frozen from cloud to surface.
But can it be too cold to snow? Sometimes! The colder it gets, the less water vapor there will be in the air…and less water vapor in the air means less chance of snow.
Sleet occurs when a snowflake falls through the atmosphere and warms up a bit before refreezing. The snowflake begins its journey frozen. As it passes through a thin layer of warm air in the atmosphere, it melts a bit.
It then re-enters another pocket of cold air before reaching the surface. The snowflake refreezes and becomes an ice pellet we call sleet. Sleet typically bounces when it hits the ground.
Freezing rain follows a similar journey as sleet, but instead of a thin pocket of warm air, freezing rain falls through a larger pocket of warm air in the middle of its journey. Freezing rain begins as snow, but when it reaches the warm pocket, it melts and becomes rain.
Before hitting the ground, it passes through a very shallow pocket of cold air, which cools it some but not enough to turn it into sleet. Instead, when the water droplet reaches the surface of the Earth and comes in contact with cold objects (such as cars, streets, or trees), it freezes immediately and turns into ice.
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Winter Weather Alerts, Watches and Advisories
Winter weather related Warnings, Watches and Advisories are issued by your local National Weather Service office. Each office knows the local area and will issue Warnings, Watches or Advisories based on local criteria. For example, the amount of snow that triggers a “Winter Storm Warning” in the Northern Plains is typically much higher than the amount needed to trigger a “Winter Storm Warning” in the Southeast.
Warnings: Take Action!
Watches: Be Prepared
Advisories: Be Aware
Here are some more key terms to understand:
- Freezing Rain: Rain that freezes when it hits the ground; creating a coating of ice on roads, walkways, trees and power lines.
- Sleet: Rain that turns to ice pellets before reaching the ground. Sleet also causes moisture on roads to freeze and become slippery.
- Wind Chill: A measure of how cold people feel due to the combined effect of wind and cold temperatures; the Wind Chill Index is based on the rate of heat loss from exposed skin. Both cold temperatures and wind remove heat from the body; as the wind speed increases during cold conditions, a body loses heat more quickly. Eventually, the internal body temperature also falls and hypothermia can develop. Animals also feel the effects of wind chill; but inanimate objects, such as vehicles and buildings, do not. They will only cool to the actual air temperature, although much faster during windy conditions.
What is a Lake Effect Snow?
Lake effect snow is common across the Great Lakes region during the late fall and winter. Lake Effect snow occurs when cold air, often originating from Canada, moves across the open waters of the Great Lakes. As the cold air passes over the unfrozen and relatively warm waters of the Great Lakes, warmth and moisture are transferred into the lowest portion of the atmosphere. The air rises, clouds form and grow into narrow band that produces 2 to 3 inches of snow per hour or more.
Wind direction is a key component in determining which areas will receive lake effect snow. Heavy snow may be falling in one location, while the sun may be shining just a mile or two away in either direction. The physical geography of the land and water is also important. National Weather Service meteorologists consider these factors as well as others when forecasting lake effect snow.
What is a Blizzard
The term "blizzard" is often tossed around when big winter storms blow in. But the National Weather service has an official definition of blizzard:
A blizzard is a storm with "considerable falling or blowing snow" and winds in excess of 35 mph and visibilities of less than 1/4 mile for at least 3 hours.
While blizzard conditions may occur for shorter periods of time, the weather service is particular about its warning system:
When all the blizzard conditions are expected, the National Weather Service will issue a "blizzard warning." When just two of the above conditions are expected, a "winter storm warning" or "heavy snow warning" may be issued.
Winter Mix, What Does This Mean?
When I use the phrase “winter mix”, it refers to some combination of snow, sleet or freezing rain/drizzle (ice).
The term is used whenever any of these are possible over a certain time frame.
Both sleet and freezing rain require a layer of above freezing air aloft. The difference is in the depth of the sub-freezing layer touching the ground (lower blue areas on diagram)
While the most common layout is for snow to occur closest to the colder air with sleet, freezing rain and rain occurring in bands toward the warmer air (usually in a southerly direction), there are exceptions.
One is terrain. An increase in elevation means colder temperatures which can change the precipitation type. Or the opposite, occasionally cold air becomes trapped in valleys and alters precipitation type.
Also, convective (rain/thunder) bands tend to cool a column of air near the ground and turning what might be a freezing rain situation into sleet.
One more condition occurs when cloud droplets exist in below freezing air (which is common) but lack a ice crystal seeding only found at colder temperatures or occasionally falling from clouds above. The result is often freezing drizzle instead of snow.
Here are the definitions:
This is liquid (rain) aloft which falls into subfreezing air near the surface deep enough to freeze the drops into ice balls. Sleet “tings” when it strikes windows. Sleet accumulates like snow but because it is essentially little ice pellets, it doesn’t accumulate nearly as fast. It actually offers some increased traction on roads when compared to snow.
Freezing Rain (Ice)
Nearly the same as sleet except that the drops stay liquid falling into a much shallower subfreezing layer at the ground. These “super-cooled” rain drops will then freeze on contact with surface objects, especially those off the ground such as trees and wires. Freezing rain producing ice accumulations over a half inch can cause branches and wires to snap from the weight. An ice storm is born!
Winter Storm Reality Check
Here's your winter storm reality check: Are you prepared?
It’s that time of year. Winter is here and with it, severe weather events are inevitable. Between frozen pipes, falling tree limbs, space heater fires, and black ice, dangers are abound when freezing temperatures combine with even slight precipitation.
Each year, winter storms create more than $1 billion in insured losses. In preparation for the 2019 winter season, the PCI has drawn up a winter storm preparedness reality check for property owners to take to ensure they are ready.
In their reality checklist, PCI poses the following questions to homeowners, renters and motorists:
- Do you allow extra space to brake when driving during the winter?
- Have you prepared an emergency travel kit for your car and/or home?
- Have you checked your attic and pipes to ensure they have proper insulation?
- Have you made sure your heating system and chimney have been cleaned and inspected?
- Have you talked with your insurance agent or company to review and understand your coverage?
- Have you made sure home smoke detectors and carbon monoxide alarms are installed and working?
If you found yourself answering “no” to any of these questions, PCI has winter storm preparedness information available in its Winter Storm Headquarters that may help.
Winter Storm Survival
- Seek some form of shelter immediately. Blowing winds can cause the wind chill to reduce your core body temperature to dangerous levels. The risk of frostbite and hypothermia increase every minute you are exposed to the cold weather.
- If you are wet, try to get dry. Lighting a small fire will not only provide warmth but will enable your clothing to dry out.
- Deep snow can actually act as an insulation from the wind and cold temperatures. Digging a snow cave can actually save your life.
- Stay hydrated, but DO NOT eat snow. (Because your body must heat the ice in order to melt it into water, you'd actually lose heat.) If you do get your water from snow, make sure to melt it before drinking it. (For example, use a heating source or indirect body heat like a canteen inside your coat, but not directly next to your skin.)
In a Car or Truck:
- Never leave your vehicle. If you are stranded, it will offer a form of protection from overexposure to the cold. A single person walking through the snow is also harder to find than a stranded car or truck.
- It is okay to run the car for short periods to provide some heat. Remember to crack the windows a small amount to allow for the circulation of fresh air. Dangerous exhaust fumes, including carbon monoxide, can build up very quickly. This is especially true if the tailpipe is buried in the snow.
- Keep yourself moving. A car offers little room for you to keep your blood flowing, but exercise is a must. Clap your hands, stomp your feet, and move around as much as possible at least once an hour. In addition to keeping your body moving, keep your mind and spirit from getting "down," depressed, or overly stressed.
- Make the car visible for a rescue. Hang bits of bright colored cloth or plastic from the windows. If the snow has stopped falling, open the hood of the car as a signal of distress.
- If the electricity goes out, use an alternative form of heat with caution. Fireplaces and kerosene heaters can be dangerous without proper ventilation. Keep children away from any alternative heat source.
- Stick to one room for heat and close off unnecessary rooms in the house. Make sure there are no air leaks in the room. Keep sunlight streaming through the windows in the day, but cover all windows at night to keep warm air in and cold outside air out.
- Keep hydrated and nourished in case the heat is out for an extended period of time. An unhealthy body will be more susceptible to the cold than a healthy one.
- Pets must also be protected from the cold. When temperatures drop below freezing, outdoor pets should be moved indoors or to a sheltered area to protect them from the cold.
Car Prep for Winter
Put a “winter supply” box in your car. This is the single most important thing you can do for your car and for your personal safety. Having a box full of winter supplies in your trunk can make all the difference when something goes wrong while traveling on a cold winter day.
Here’s a quick list of items you should include in that box: a flashlight, road flares, a first-aid kit, a few blankets, a change of warm clothes for the driver, a few extra pairs of gloves, a radio, a charged cellphone for 911 calls, a bag of sand (for traction), an extra ice scraper and some high-energy snacks (like nuts or jerky).
My family keeps a pair of large Rubbermaid containers in the garage through the spring, summer and fall. The containers always carry these items, and we put those containers in our cars during the winter months after checking them over at the start of the season.
Check your engine coolant and antifreeze levels. Antifreeze is the magical substance that keeps your engine from freezing during those times of the year when you feel like you are freezing. Without it, your engine can freeze, leaving you in a real pickle at a time when it’s dangerous to be stranded.
A kit for checking your engine coolant levels is available at almost every auto supply store. Using that kit can let you know quickly if you have an appropriate coolant mix. You can also directly check your antifreeze levels by following the instructions in your car’s manual. Adding more antifreeze is very simple, too, if you need to do it.
Check your tire pressure and tread depth. Good tires are the key to staying on the road and keeping safe when the weather is questionable and snow and ice are falling from the sky. You can do your part to ensure your tires are in good shape with just a few simple steps.
First, check your tire pressure with a simple gauge sold at any auto supply store. Follow your manual’s recommendations for pressure level, and if your tires need air, fill them up at the gas station. Most gas stations offer free tire air fill-ups.
You should also make sure your tires have appropriate amounts of tread on them. The simple test is the “Lincoln test” – just insert a penny into your tire’s tread with the top of Lincoln’s head pointing inward toward the tire. If you can see all of Lincoln’s head, you need to replace the tire before winter weather begins.
If you live in a particularly wintry climate, you may want to consider installing winter tires before the season begins, as they will make all the difference when it comes to getting around.
Protecting Your Family - Winter Storm Prep
How to Prepare Your Family for a Winter Storm
- Talk with your family about what to do if a winter storm watch or warning is issued. Discussing winter storms ahead of time helps reduce fear, particularly for young children.
- Have your vehicle winterized before the winter storm season to decrease your chance of being stranded in cold weather.
- Have a mechanic check your battery, antifreeze, wipers and windshield washer fluid, ignition system, thermostat, lights, flashing hazard lights, exhaust system, heater, brakes, defroster, and oil.
- Install good winter tires with adequate tread. All-weather radials are usually adequate but some jurisdictions require vehicles to be equipped with chains or snow tires with studs.
- Keep in your vehicle: - A windshield scraper and small broom - A small sack of sand for generating traction under wheels and a set of tire chains or traction mats - Matches in a waterproof container - A brightly colored (preferably red) cloth to tie to the antenna - An emergency supply kit, including warm clothing.
- Keep your vehicle’s gas tank full so you can leave right away in an emergency and to keep the fuel line from freezing.
- Keep a supply of non-clumping kitty litter to make walkways and steps less slippery.
- Service snow removal equipment before the winter storm season and maintain it in good working order.
- Keep handy a warm coat, gloves or mittens, hat, water-resistant boots, and extra blankets and warm clothing for each member of the household.