Satellite Maps
Water Vapor
Region: 
Toggle National and Regional Views
Click the blue-button above to toggle between National/World and Regional views. View persists until toggle back.
For adding explicit book-marks to directly access preferred weather maps, click here to visit our FAQ page.
VA - Roanoke Radar Map AZ - Prescott Radar Map CA - Bakersfield Radar Map GA - Columbus Radar Map NC - Charlotte Radar Map KY - Bowling Green Radar Map AR - Little Rock Radar Map MS - Vicksburg Radar Map VA - Staunton Radar Map OH - Dayton Radar Map CT - Hartford Radar Map NY - Binghamton Radar Map IL - Springfield Radar Map MI - Cadillac Radar Map NH - Berlin Radar Map FL - Key West Radar Map LA - New Orleans Radar Map TX - Brownsville Radar Map TX - San Antonio Radar Map FL - Saint Petersburg Radar Map IA - Des Moines Radar Map MN - Saint Cloud Radar Map ND - Bismarck Radar Map SD - Pierre Radar Map NE - North Platte Radar Map OK - Lawton Radar Map KS - Salina Radar Map MO - Jefferson City Radar Map CO - Denver Radar Map UT - Provo Radar Map WY - Riverton Radar Map MT - Lewistown Radar Map NV - Reno Radar Map ID - McCall Radar Map OR - Redmond Radar Map WA - Tacoma Radar Map NM - Roswell Radar Map
Learn about Water Vapor
View Detailed Information »
Overview
The Water Vapor map shows areas of moist and dry air at mid-levels of the atmosphere (about 12,000 feet). Water vapor or water vapour, also aqueous vapor, is the gas phase of water. Water vapor is one state of the water cycle within the hydrosphere. Water vapor can be produced from the evaporation of liquid water or from the sublimation of ice. Under normal atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation.

Evaporation/sublimation
Whenever a water molecule leaves a surface, it is said to have evaporated. Each individual water molecule which transitions between a more associated (liquid) and a less associated (vapor/gas) state does so through the absorption or release of kinetic energy. The aggregate measurement of this kinetic energy transfer is defined as thermal energy and occurs only when there is differential in the temperature of the water molecules. Liquid water that becomes water vapor takes a parcel of heat with it, in a process called evaporative cooling. The amount of water vapor in the air determines how fast each molecule will return back to the surface. When a net evaporation occurs, the body of water will undergo a net cooling directly related to the loss of water.

Evaporative cooling is restricted by atmospheric conditions. Humidity is the amount of water vapor in the air. The vapor content of air is measured with devices known as hygrometers. The measurements are usually expressed as specific humidity or percent relative humidity. The temperatures of the atmosphere and the water surface determine the equilibrium vapor pressure; 100% relative humidity occurs when the partial pressure of water vapor is equal to the equilibrium vapor pressure. This condition is often referred to as complete saturation. Humidity ranges from 0 gram per cubic metre in dry air to 30 grams per cubic metre (0.03 ounce per cubic foot) when the vapour is saturated at 30°C.

Another form of evaporation is sublimation, by which water molecules become gaseous directly from ice without first becoming liquid water. Sublimation accounts for the slow mid-winter disappearance of ice and snow at temperatures too low to cause melting.

Condensation
Water vapor will only condense onto another surface when that surface is cooler than the temperature of the water vapor, or when the water vapor equilibrium in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface. The water molecule brings a parcel of heat with it. In turn, the temperature of the atmosphere drops slightly. In the atmosphere, condensation produces clouds, fog and precipitation (usually only when facilitated by cloud condensation nuclei). The dew point of an air parcel is the temperature to which it must cool before water vapor in the air begins to condense.

Also, a net condensation of water vapor occurs on surface when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition, the direct formation of ice from water vapor, is a type of condensation. Frost and snow are examples of deposition.
Advertisements
Track Severe Weather on mobile