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The weather at zero degrees

The weather at zero degrees

Posted on 15 Nov 2023

To appreciate the beauty of a snowflake, one must stand out in the cold. - Aristotle.

When temperatures drop to zero degrees, water takes on a seemingly mystical transition from its liquid to solid state. This solid has shaped and molded our planet and our lives, has created devastation, wrecked ships, inspired explorers and preserved our food. Understanding this transition, and importantly predicting when it may happen is one of the most fundamental elements of our modern society. This knowledge can tell us when our cars might slide on the road, when we need to protect our crops, turn on our heating, and protect our renewable energy infrastructure.

Ice, in all its forms, from the largest of glaciers to the lightest of snowflakes, plays an intrinsic part in our past, present and future. 

The Ice Rivers

Glaciers are majestic, complex giant rivers of ice that cover 10% of the earth’s surface and hold up to an estimated 70% of the world’s supply of fresh water. They are constantly moving through their own weight, traveling at an average of 1 meter per day. Features such as crevasses form, appearing as cracks in the glacier formed when two parts of the glacier move at different rates or directions. 

Their blue appearance is due to the frozen water being less capable of absorbing blue light than other wavelengths - they also lack the small air bubbles that normally gives ice a whiter look. As a whole, although the glacier is solid ice, it behaves as a viscous liquid … the archetypal “river of ice”. 

They shape our landscape, converting ‘V’ shaped valleys created by water erosion to flatter, ‘U’ shaped ones. They have even compressed the surface of the earth’s mantle. In the UK, ancient glaciation only affected the northern areas, causing the entire land mass to ‘tilt’. Since the ice retreated, the land is slowly rebounding, with the northern areas rising by about 10 cm per century, and the southern areas being lowered by about 5 cm. 

When a glacier is found in the more temperate areas, it can act as a valuable source of water during the summer months. The melt water is often used for the irrigation of crops, hydropower and filling artificial lakes.

These giants are also susceptible to changes in global climate, and have been reducing in size since the 19th century. This rate of loss of ice is increasing, with an estimated global loss of 210 gigatons per year. As the glaciers melt, more water is released into the oceans, creating higher sea levels, coastal flooding, erosion, and a higher likelihood of coastal storms and hurricanes.   

The OpenWeather Global Weather Alerts can help give valuable prior warning through push notifications sourced from worldwide national weather warning systems. These alerts are supplied in a uniform and consistent way, and can also include alert updates and cancellations.


Snowflakes form from a single, often microscopic particle such as pollen or dust. The snowflake then ‘grows’ into a unique crystal shape. This shape varies according to the temperature that they were formed in, with thin needle-like ice crystals that form at about -2C, while a lower temperature of -5C will lead to very flat plate-like crystals. Snow is different to sleet, which is in effect frozen rain, or hail, which are sleet droplets that collect rain and freeze as they fall. 

Although a single snowflake may be seen as a thing of beauty and intrigue, when they fall in mass (a blizzard may have 5 quintillion snowflakes), they can cause travel and infrastructure challenges. Different countries have taken various measures to try to keep their road systems safe and efficient:

Sweden, Germany plus a number of other European and Scandinavian countries have a legal requirement for drivers to own and use winter tyres that are specifically designed to cope with cold temperatures, as well as slippery driving conditions. They also require the use of snow chains, and other safety equipment to reduce the risk of road accidents and collisions.

Japan, Iceland and other Nordic countries are experimenting with heated roads. With this, pipes are installed underneath the tarmac that have heated water pumped through when the temperatures fall below freezing. This prevents the formation of ice and the collection of snow. Although these roads are very expensive to install and run, they are effective at keeping key routes safe and clear during cold periods.

Other countries such as Finland prefer to put the emphasis on driver competence, with far more stringent driving test requirements, including the mandatory practice of controlling a vehicle while in a skid. 

Often being able to predict snow, and other hazardous road conditions can help all road users plan their journey ahead of time, no matter their geographic location. The OpenWeather Road Risk API can give detailed weather information, including adverse road conditions, with up to minute granularity for given points along a route, as well as historic, current and forecast data. 


When the mercury falls to freezing, water trapped in soil turns to ice. When the soil remains frozen for over two years, it is known as permafrost. The frozen soil actually has the effect of heating the air around it, as heat is released when water turns to its solid state. Also, as frozen soil conducts heat better, it can release more stored sun energy into the atmosphere than non-frozen soil.

Permafrost can have the effect of supporting local wetland environments; during summer months, the top levels of soil may thaw, leaving the lower levels frozen. The frozen layer acts as a waterproof layer, preventing the topsoil from drying out, allowing for small pools of water, ponds, lakes and marshes to form. These pools in turn support a varied and diverse ecosystem of animals and plants.

Although frost can be beneficial to certain ecosystems and environments, it can also be harmful to plants when ice forms inside the tissue. Unseasonal frosts can damage crops, reducing their yield, and their overall quality. There are a number of measures that can be taken by farmers to help mitigate the risk, including selective pruning, avoiding tilling the soil during frosty periods, as well as the introduction of heated pipes to stop the frost in the soil itself. 

From the smallest of snowflakes to the largest of glaciers, frozen water continues to affect our lives, infrastructure and environment. Understanding when the tipping point between water in its liquid and solid forms may occur can be a pivotal piece of information in so many ways.

About OpenWeather:

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