Safe ice thickness for walking is 10 cm (3.9 in). What about skiing, ice fishing, and driving a huge truck

Meteorologists, lifeguards, outdoor enthusiasts, and simply those who enjoy observing nature agree that ice is never 100 percent safe. Yes, you can walk and even drive various vehicles on the ice, but that doesn't mean you can't fall through even when it's "safe" thick. In this article, let's understand how to behave on frozen water.

What is safe ice thickness?

Just in case, for those who live all their life somewhere in tropics but are going on a trip to the northern hemisphere to America, Europe, or Asia: in winter, in northern parts of the world, when the air temperature is below zero, the water in enclosed and usually small bodies of water freeze and become covered with ice. This may be a small lake or river, but also an entire bay (part of the sea).

The lower the air temperature and the longer it lasts (say, 10 days rather than one or two), the thicker layer of ice forms on the water.

On a frozen lake and other open water you can also continue to do some summer sports and outdoor activities: snowshoeing instead of hiking, ice fishing instead of fishing, winter kite- and windsurfing instead of a reguler ones, and so on. And of course, ice skating and skiing.

Knowing the precise thickness of the ice is important so as not to fall through on the frozen water. In this case, we are talking about specific figures, not just "the ice looks solid". Even if it looks that way, the impression can be misleading. So this is what called "safe ice thikness".

In addition, it varies depending on the type of activity that you are going to do on the ice: from simply walking and sitting in one place for a long time during ice fishing to crossing extensive lakes and rivers on heavy vehicles carrying vital cargo from one shore to another.

Spencer Davis / Unsplash

Anyway, then a logical question arises: who measures safe ice thikness and how?

This can be done by the staff of winter (usually skiing) resorts, national parks, fishing, and other outdoor clubs and the like, or by government conservation agencies.

For example, in the United States it is the Department of Natural Resources. Each state has a branch of this service (for example, in Iowa, Michigan, Wisconsin, Colorado), which notifies us that the ice thickness is safe at specific bodies of water — and therefore, it is possible to move through them at the time of publication of the message.

And this is an example of an ice thickness warning and safety recommendations from Joe Larscheid, chief of fisheries for the Iowa DNR, in the middle of December 2020: “Check ice thickness as you make your way to your favorite fishing spot. Ice conditions change constantly and its thickness can vary across the lake. Trust your instincts — if the ice does not look right, don’t go out.”

So you can find out how thick the ice is in your area from such reports from local officials. You can also measure the thickness of the ice yourself. But it should be done very carefully and only near the shore.

There are specific tools you can use to easily dig a hole:

ice chisel — a long metal rod with a sharp blade at one end;
ice auger — it could be a hand auger (you'll have to dig through using your own strength), electric or gas (more easily);
cordless drill — attach a 5—8 inch wood auger bit with a spiral around the shaft to your drill.

Once you've reached the water, you can measure the depth with a tape measure.

So let's finally look at the specific values of safe ice thickness for certain types of activity on the ice. If you know the thickness, you can go out on the ice. Or not.

Safe ice thickness chart. Sources: Canadian Red Cross and Life Saving Society, North Dakota Game and Fish Department of the US, and others). Illustration: Valeriya Milovanova / Windy.app

Safe ice thickness to walk on

4 inches (10.1 centimeters, cm) is a safe ice thickness for walking, skating or skiing, ice fishing and other similar activities. In all of these cases you should be alone to stay safe on ice. This kind of ice can hold as much as 200 pounds (90 kg).
5 inches (12.7 cm) is a safe ice thickness to walk in a small group of people in a single line with a total weight of up to several hundred kg.

Safe ice thickness to drive on

6 inches (15.5 cm) is a safe ice thickness for snowmobiles or ATV (all-terrain vehicle) weighing up to 1.5—2 tons.
8–12 inches (20–30 cm) is a safe ice thickness for a car or small truck weighing 2.5—3.5 tons.
12–15 inches (30–38 cm) is a safe ice thickness for trucks or midsize SUV weighing up to 8—10 tons.

Of course, you can also travel on thicker ice. It could be 20 inches or 50 centimeters thick (supports 25 tons), 30 inches or 76 centimeters (70 tons), and 36 inches or 91 centimeters (100 tons). Generally, this ice is found on bodies of water in the northern territories beyond the Arctic Circle. Ice is rarely thicker than this in more southerly latitudes.

In contrast, you can't go out on ice less than 4 inches thick, let alone drive a vehicle on it, because it's not safe.

Tom Barrett / Unsplash

How to stay safe on the ice?

To stay safe on the ice, knowing just its safe thickness is not enough. There are at least a few other important things to know.

In addition to air temperature, ice thickness is affected by many different factors: water depth, the size of the waterbody and fluctuations in water levels, currents and moving water, chemicals like salt, logs, rocks, and docks absorbing heat from the sun and melting the surroundings, and others.

The ice thickness is also affected by the quality of the ice (yes, it varies), it should be mentioned separately.

The quality of the ice can be determined by its color. And this may be the most simple way to know the ice thickness safely from the shore, without getting out special tools, which you probably don't have.

How to determine if the ice is safe by its color:

New, clear, and blue looking ice is usually good and hard ice. It forms when the temperature is at least -8 ºC (46.4 °F) three weeks in a row. The colder, the faster blue ice forms.
Ice ranging in color from white to opaque, as well as ice covered with snow, has air cavities inside. It's formed by wet snow freezing on top of already existing ice. This means that the ice is less strong and cracks form easily on it. In this case, the safe thickness of the ice should be multiplied by at least two.
Gray and black ice is the worst "soft" ice. It's "rotting". The grey color indicates water, meaning the ice will not support much weight. This ice should be avoided, never go out on it. Melting ice occurs even if the air temperature is below 32°F (0°C).
Mottled and slushy is the most unsafe kind of ice. It is not so much its color but its texture that is important. It has a very poor, unstable texture, even if it looks sturdy on top. It is not suitable for even a footstep.

As a general rule: ice that is neither new nor clear is half as thick as clear ice (that is, it must be twice as thick to be able to go out on it).

Ice strength on rivers is usually 15% lower than on small lakes.

Randy Fath / Unsplash

Weather conditions are also everywhere and always different. Even if the temperature is below 0 degrees Celsius for a few days, it is freezing outside and ice has been forming on lakes and rivers for a long time, always check the situation before you go out on the ice.

Variable temperatures also suggest that cracks may be forming on the ice.

In addition — and this is also very important — the thickness of ice is not the same everywhere throughout the body of water. Some parts of, let's say a lake, may have thick ice, while others do not. Usually, the ice is less thick closer to the shore.

So to stay safe on the ice, follow these additional recommendations:

Do not go out on the ice in late fall or late spring — usually, the ice at the beginning and end of the winter season is not firm and can crack easily. In contrast, ice in mid-winter is strongest if the temperature is sub-zero and other conditions apply.
Do not go out on the ice near moving water — rivers, streams, and so on, or lakes with strong water movement.
Do not go out on the ice where there are cracks.
Do not go out on the ice alone or in large groups, or without a local person who knows the weather, climate, and nature of the area. Group rides in two and more cars can be even more dangerous.
Do not go out on the ice that cannot be seen under the snow. Too much snow puts extra stress on the frozen water surface.
Do not go out on the ice without survival gear: life jacket, ice pick (a way to get yourself out of the water), working cell phone and a power bank to charge it, length of rope, ice auger, hand warmers, a basic first aid kit, extra dry clothes including a pair of gloves and other.
Do not totally count on survival gear. Keep in mind that in cold water the life jacket is only half useful: it will help you stay afloat, but it will not protect you from the icy water. Staying in it for a long time is deadly.
Do not drive on ice without taking the following precautions: seatbelt off, doors unlocked, light on, windows open, travel at low speeds. Don't be embarrassed if it is the opposite of what we are used to on the road.
Do not drive on ice in the dark — preferably, despite the short daylight hours in winter.

The most important: if you have any doubts about the ice thickness, don't go to the ice.

Where to get a snow forecast?

There is a whole Snow Weather Profile in the Windy.app, where you can get a preset of 10+ weather parameters, indexes, data, and charts created especially for winter sports like snowshoeing, skiing, snowboarding, ice fishing and other. In particular, in the profile you can get:

General weather condition
Air temperature at the top and bottom stations of a ski resort, as well as in the middle
Cloud coverage
Rain ans snow chart
Fresh snow for the same altitudes as written above
Snow depth
Last snowfall date
Freezing level chart
Wind speed, direction and gusts

Snow Weather Profile in the Windy.app for iOS

Weather elements of the Snow Weather Profile in the Windy.app for iOS

To set up Snow Weather Profile:

1. Go to your favorite or the nearest spot in the app.

2. Open Snow Weather Profile by an icon right to weather forecast modes.

3. Get weather forecast for the next 10 days.

The precipitation and wind forecast for the ski resort and the region in which it is located can also be viewed visually on the Weather Map. To do this, click on the map icon at the top of the screen in the widget and select the Precipitation layer on it.

Precipitation Map of the Dolomites in the Windy.app for iOS

However, in addition to the snow forecast, we also recommend checking the real-time weather from the nearest weather station as well as weather history.

Weather stations for ski resorts

In the Windy.app you can find weather stations right on the spot screen. It includes information about air temperature and wind. You can also get the forecast for the station as a spot. To do so, click on the "Get the forecast" icon. More: you can compare wind data from the weather station with the forecast. Click on the "Detailed analysis" icon and check the whine line in the comparison chart in the forecast table.

Weather station in the Trentino-Alto Adige region of Italy in the Windy.app for iOS

Snow history for ski resorts

Another useful thing in the Windy.app is weather history for ski resort with precipitation data on the particular day a year ago, several years ago, a decade ago as well as the average values for months and years.. This information will help you predict the snow on the day you need it. Again, there is no guarantee that if there was snow in this area on this day every year during the last 10 years, it will be the same this time, but it increases the chances a little bit.

In some other resources you can also find information about the snowfall in particular, including the snowiest week of the year at the ski resort, the number of snowy days in a week, the average snow on this day based on weather data for the last years, and other historical data.

Precipitation history in the Windy.app for iOS

This post was originally published on the Windy.app blog on January 21, 2021.

Text: Ivan Kuznetsov, an outdoor journalis, editor and writer from the Dolomites, Italy, and Karelia, Finland, with 10+ years of professional experience. His favorite sports are cycling, hiking, and sauna.

Cover photo: Spencer Davis / Unsplash