Fog

Fog is like a low cloud.

It stays near the ground. It is made of tiny water drops. These drops hang in the air.

Fog forms when water in the air turns into drops. This can happen when the air cools down.

Sometimes, the water turns into tiny bits of ice.

Fog can be thick or thin. Mist is a type of thin fog. Fog makes it hard to see things. It can make it hard to travel.

Fog can happen near lakes or oceans. It can also happen in valleys. Sometimes, it comes from plants.

It can even bring light snow or drizzle. Fog is a very cool part of our world.

Fog is a low cloud that stays near the ground.

It is made of tiny water droplets or ice crystals. These small bits hang in the air. Fog happens when water vapor condenses. Condensation is when water in the air turns into liquid drops.

This can happen in many ways. Air can cool down over warm water. Wind can move moist air over cold ground. This is called advection fog.

Another kind is radiation fog. This forms at night when the ground cools down. The cool ground then cools the air near it. This can make fog in valleys or swamps. Sometimes, fog can make tiny drops of rain called drizzle. If it is very cold, the drops can freeze. This is called freezing fog.

In the Arctic, the droplets can turn into ice crystals. We call this ice fog. Fog makes it hard to see. It can change how people travel by sea or land.

Fog is a low-lying cloud that stays near the Earth's surface.

It is made of tiny water droplets or ice crystals hanging in the air. You might think it is just like a cloud, but fog is different because it sits so low. It can make it hard to see things clearly. This can affect how people travel by ship or car. It can even change how people fight in wars.

Fog forms through a process called condensation. This happens when water vapor, which is water in a gas form, turns back into liquid. The vapor often gathers around tiny bits of dust, salt, or ice. These bits are called condensation nuclei.

When the air becomes very moist, these droplets stay suspended in the air. This usually happens when the air reaches a relative humidity near 100 percent. If the droplets get big enough, they might fall as a light rain called drizzle.

There are several ways that fog can form. Radiation fog happens at night when the ground cools down. The cool ground then chills the air right above it. This often happens in valleys or swampy areas.

Another type is advection fog. This occurs when wind moves warm, moist air over a cold surface. You can see this near the California coast when moist air hits cold ocean water.

There is also frontal fog, which forms when raindrops evaporate into cool air.

Some fog is very cold and can create ice. Freezing fog happens when liquid droplets freeze onto surfaces. This creates white ice called rime. In the western United States, people sometimes call this "pogonip."

The word comes from the Shoshone word for cloud. In very cold places like the Arctic, we see ice fog. This is when the droplets are actually tiny ice crystals. This only happens when temperatures are at or below -40 degrees Celsius.

Fog is a part of the natural weather cycle we see every day. It is linked to how the Earth holds heat and moisture. For example, the sun warming the ground in the morning can make fog evaporate. In the winter, longer nights give the ground more time to cool and make radiation fog.

Whether it is a thin mist or a thick bank, fog shows how air and water work together. It reminds us that even the air around us is full of moving parts.

Fog is a visible aerosol made of tiny water droplets or ice crystals. These particles are held in the air near the Earth's surface. You can think of fog as a low-lying cloud. It often looks like a stratus cloud, which is a flat, layered cloud type. Fog is heavily influenced by wind, local land shapes, and nearby water. Because it can make it hard to see, fog affects many human activities. It impacts shipping, travel, and even warfare.

Fog forms through a process called condensation. This occurs when water vapor, which is water in a gas form, turns into liquid. For this to happen, the water vapor molecules must combine into tiny droplets. These droplets usually gather around small particles called condensation nuclei. These nuclei can be bits of dust, ice, or salt. Sea fog is a specific type that forms when vapor condenses on salt particles. Fog usually appears when the relative humidity is near 100 percent.

There are several distinct ways that fog can form. Radiation fog is one common type. It forms after sunset during clear and calm conditions. The Earth's surface loses heat and cools the air touching it through conduction. This creates a temperature inversion, where cool air is trapped under warmer air. This type of fog is most likely to occur in valleys or swampy areas. It is often thickest shortly after sunrise before the sun evaporates the droplets.

Another type is advection fog. This happens when wind moves moist air over a cool surface. This process is called advection. It is very common at sea when warm air meets cooler waters. Along the California coast, a cold front or a pressure gradient can push this marine layer onto land. In the summer, a low-pressure trough can also draw this fog inland. This type of fog can be quite complex depending on the terrain.

Frontal fog forms near a weather front. It works much like a stratus cloud. Raindrops fall from warm air and evaporate into cooler air near the ground. This makes the air saturated, so the vapor condenses into fog. There is also hail fog. This occurs near large amounts of hail. The hail cools the air and adds moisture as it melts or evaporates. This fog is often very dense and appears abruptly.

Extreme cold can create very different kinds of fog. Freezing fog happens when liquid droplets freeze upon hitting a surface. This creates white ice known as rime. In the western United States, people call this pogonip. The name comes from the Shoshone word for cloud. In the Columbia Plateau, these inversions can last for three weeks. In even colder regions like the Arctic, we find ice fog. This is when the droplets are actually tiny ice crystals. This requires temperatures at or below -40 degrees Celsius.

Fog is closely linked to the movement of heat and moisture in our atmosphere. The thickness of a fog layer depends on the altitude of the inversion boundary. This boundary changes based on atmospheric pressure. High pressure can squash a fog bank, while low pressure allows it to expand upward. Fog can also produce drizzle. This happens when droplets coalesce, or join together, into larger drops. By studying fog, we learn how the air, water, and Earth's surface interact.