That's four-thousandths of an inch. But most are even smaller than that, around 0. Then there's the case where precipitation does fall from a cloud, but evaporates in drier air below the cloud. When noticeable, it's called virga. You can sometimes see this as streaks dropping from a cloud, but disappearing before reaching the ground.
Copyright KCBD. All rights reserved. Skip to content. Local Listings. Latest Newscasts. Weather Cams. Send Us Your Weather Photos. Download the Weather App. As the nights are getting longer in autumn, we often have clear and cloudless skies at night. The conditions help the ground, and the air near the ground, to rapidly cool during evening are clear and cloudless skies and long nights. These are the type of conditions we often have in autumn.
As the air cools during the longer night the relative humidity increases, which can result in to fog formation. Windy mornings are fog free as strong winds mix the air near the ground with the drier, warmer air above. As autumn progresses, we will see a fog during the day forming over the unfrozen lakes. This fog, called evaporation fog, forms when colder air moves over warmer water. Clouds regulate the flow of radiant energy into and out of Earth's climate system.
They influence the Earth's climate by reflecting incoming solar radiation heat back to space and outgoing radiation terrestrial from the Earth's surface. Often at night, clouds act as a "blanket," keeping a portion of the day's heat next to the surface. Changing cloud patterns modify the Earth's energy balance, and, in turn, temperatures on the Earth's surface. As we said, clouds form in the atmosphere because air containing water vapor rises and cools.
The key to this process is that air near the Earth's surface is warmed by solar radiation. But, do you know why the atmosphere cools above the Earth's surface? Generally, air pressure, is the reason. The pressure weight , called barometric pressure, that results is a consequence of the density of the air above. At higher altitudes, there is less air above, and, thus, less air pressure pressing down. The barometric pressure is lower, and lower barometric pressure is associated with fewer molecules per unit volume.
Therefore, the air at higher altitudes is less dense. As the total heat content of a system is directly related to the amount of matter present, it is cooler at higher elevation This means cooler air. On California's Marin Headlands, facing away from the Golden Gate Bridge, the August heat hits the cool air from the Ocean, creating a very thick fog that tends to sit low on the ground. Condensation also occurs at ground level, as this picture of a cloud bank in California shows.
The difference between fog and clouds which form above the Earth's surface is that rising air is not required to form fog. Fog develops when air having a relatively high humidity comes in contact with a colder surface, often the Earth's surface, and cools to the dew point. Additional cooling leads to condensation and the growth of low-level clouds. Fog that develops when warmer air moves over a colder surface is known as advective fog. Another form of fog, known as radiative fog, develops at night when surface temperatures cool.
If the air is still, the fog layer does not readily mix with the air above it, which encourages the development of shallow ground fog. You probably see condensation right at home every day. If you wear glasses and go from a cold, air-conditioned room to outside on a humid day, the lenses fog up as small water droplets coat the surface via condensation. People buy coasters to keep condensed water from dripping off their chilled drink glass onto their coffee tables.
Condensation is responsible for the water covering the inside of a window on a cold day unless you are lucky enough to have double-paned windows that keep the inside pane relatively warm and for the moisture on the inside of car windows, especially after people have been exhaling moist air.
All of these are examples of water leaving the vapor state in the warm air and condensing into liquid as it is cools. Air, even "clear air," contains water molecules. Clouds exist in the atmosphere because of rising air. As air rises and cools the water in it can "condense out", forming clouds.
Since clouds drift over the landscape, they are one of the ways that water moves geographically around the globe in the water cycle. A common myth is that clouds form because cooler air can hold less water than warmer air—but this is not true. As Alistair Fraser explains in his web page " Bad Meteorology ": "What appears to be cloud-free air virtually always contains sub microscopic drops, but as evaporation exceeds condensation, the drops do not survive long after an initial chance clumping of molecules.
As air is cooled, the evaporation rate decreases more rapidly than does the condensation rate with the result that there comes a temperature the dew point temperature where the evaporation is less than the condensation and a droplet can grow into a cloud drop.
When the temperature drops below the dew-point temperature, there is a net condensation and a cloud forms," accessed on Sep. You've seen the cloud-like trails that high-flying airplanes leave behind and you probably know they are called contrails. Maybe you didn't know they were called that because they are actually condensation trails and, in fact, are not much different than natural clouds.
If the exhaust from the airplane contains water vapor, and if the air is very cold which it often is at high altitudes , then the water vapor in the exhaust will condense out into what is essentially a cirrus cloud.
As a matter of fact, sailors have known for some time to look specifically at the patterns and persistence of jet contrails for weather forecasting.
On days where the contrails disappear quickly or don't even form, they can expect continuing good weather, while on days where they persist, a change in the weather pattern may be expected. Contrails are a concern in climate studies as increased jet traffic may result in an increase in cloud cover. Several scientific studies are being conducted with respect to contrail formation and their impact on climates. Cirrus clouds affect Earth's climate by reflecting incoming sunlight and inhibiting heat loss from the surface of the planet.
It has been estimated that in certain heavy air-traffic corridors, cloud cover has increased by as much as 20 percent. Source: National Weather Service: What is a contrail and how does it form? Condensation causes clouds.
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