Advanced Hydrologic Prediction Service (AHPS)
A web-based suite of accurate and information-rich forecast products. They display the magnitude and uncertainty of occurrence of floods or droughts, from hours to days and months in advance. These graphical products are useful information and planning tools for many economic and emergency managers.
Anchor Ice
In hydrologic terms, submerged frazil ice attached or anchored to the river bottom, irrespective of its formation.
Anchor Ice Dam
An accumulation of anchor ice which acts as a dam and raises the water level.
Black Ice
1. Slang reference to patchy ice on roadways or other transportation surfaces that cannot easily be seen.

2. In hydrologic terms, transparent ice formed in rivers and lakes.
Border Ice
In hydrologic terms, an ice sheet in the form of a long border attached to the bank or shore.; shore ice.
Brackish Ice
In hydrologic terms, ice formed from brackish water.
Brash Ice
In hydrologic terms, accumulation of floating ice made up of fragments not more than 2 meters across; the wreckage of other forms of ice.
Clear Ice
A thin coating of ice on terrestrial objects, caused by rain that freezes on impact. The ice is relatively transparent, as opposed to rime ice, because of large drop size, rapid accretion of liquid water, or slow dissipation of latent heat of fusion.
Columnar Ice
In hydrologic terms, ice consisting of columnar shaped grain. The ordinary black ice is usually columnar-grained.
Consolidated Ice Cover
In hydrologic terms, ice cover formed by the packing and freezing together of floes, brash ice and other forms of floating ice.
Corn Snow Ice
In hydrologic terms, rotten granular ice.
Deformed Ice
In hydrologic terms, a general term for ice which has been squeezed together and forced upwards and downwards in places. Subdivisions are rated ice, ridge ice, hummocked ice, and other similar deformations.
Diffuse Ice
In hydrologic terms, poorly defined ice edge limiting an area of dispersed ice; usually on the leeward side of an area of floating ice.
Drifting Ice
In hydrologic terms, pieces of floating ice moving under the action of wind and/ or currents.
Duration of Ice Cover
In hydrologic terms, The time from freeze-up to break-up of an ice cover.
Dynamic Ice
In hydrologic terms, pressure due to a moving ice cover or drifting ice. Pressure occuring at movement of first contact termed Ice Impact Pressure
Emergency Services
In hydrologic terms, services provided in order to minimize the impact of a flood that is already happening. These measures are the responsibility of city, or county emergency management staff and the owners or operators of major, or critical facilities. Some examples of emergency services are flood warning and evacuation, flood response, and post flood activities.
Flooded Ice
In hydrologic terms, ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow.
Frazil Ice
In hydrologic terms, fine spicules, plates, or discoids of ice suspended in water. In rivers and lakes, frazil is formed in supercooled, turbulent water.
Grounded ice
In hydrologic terms, ice that has run aground or is contact with the ground underneath it
Hanging (ice) dam
In hydrologic terms, a mass of ice composed mainly of frazil or broken ice deposited underneath an ice cover in a region of low flow velocity.
HSA (Hydrologic Service Area)
A geographical area assigned to Weather Service Forecast Office's/Weather Forecast Office's that embraces one or more rivers.
Hummocked Ice
In hydrologic terms, ice piled haphazardly one piece over another to form an uneven surface.
Hydrologic Service Area
HSA. A geographical area assigned to Weather Service Forecast Office's/Weather Forecast Office's that embraces one or more rivers.
Ice Age
A time of widespread glaciation.
Ice Boom
In hydrologic terms, a floating structure designed to retain ice.
Ice Bridge
In hydrologic terms, a continuous ice cover of limited size extending from shore to shore like a bridge.
Ice Crystals
A barely visible crystalline form of ice that has the shape of needles, columns or plates. Ice crystals are so small that they seem to be suspended in air. Ice crystals occur at very low temperatures in a stable atmosphere.
Ice Fog
(Also called ice-crystal fog, frozen fog, frost fog, frost flakes, air hoar, rime fog, pogonip.) A type of fog, composed of suspended particles of ice; partly ice crystals 20 to 100 micron in diameter, but chiefly (especially when dense) ice particles about 12–20 micron in diameter, formed by direct freezing of supercooled water droplets with little growth directly from the vapor. It occurs at very low temperatures, and usually in clear, calm weather in high latitudes. The sun is usually visible and may cause halo phenomena. Ice fog is rare at temperatures warmer than -30°C, and increases in frequency with decreasing temperature until it is almost always present at air temperatures of -45°C in the vicinity of a source of water vapor. Such sources are the open water of fast-flowing streams or of the sea, herds of animals, volcanoes, and especially products of combustion for heating or propulsion. At temperatures warmer than -30°C, these sources can cause steam fog of liquid water droplets, which may turn into ice fog when cooled (see frost smoke). See ice-crystal haze, arctic mist.
Ice Gorge
In hydrologic terms, the gorge or opening left in a jam after it has broken.
Ice Jam
In hydrologic terms, a stationary accumulation that restricts or blocks streamflow.
Ice Nucleus
Any particle that serves as a nucleus in the formation of ice crystals in the atmosphere.
Ice Pellets
(abbrev. IP) Same as Sleet; defined as pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes. These pellets of ice usually bounce after hitting the ground or other hard surfaces. A Winter Storm Warning is issued for sleet or a combination of sleet and snow based on total accumulation which is locally defined by area.
Ice Push
In hydrologic terms, compression of an ice cover particularly at the front of a moving section of ice cover.
Ice Run
In hydrologic terms, flow of ice in a river. An ice run may be light or heavy, and may consist of frazil, anchor, slush, or sheet ice
Ice Shove
In hydrologic terms, on-shore ice push caused by wind, and currents, changes in temperature, etcetera.
Ice Storm
An ice storm is used to describe occasions when damaging accumulations of ice are expected during freezing rain situations. Significant accumulations of ice pull down trees and utility lines resulting in loss of power and communication. These accumulations of ice make walking and driving extremely dangerous. Significant ice accumulations are usually accumulations of ¼" or greater.
Ice Storm Warning
This product is issued by the National Weather Service when freezing rain produces a significant and possibly damaging accumulation of ice. The criteria for this warning varies from state to state, but typically will be issued any time more than 1/4" of ice is expected to accumulate in an area.
Ice Twitch
In hydrologic terms, downstream movement of a small section of an ice cover. Ice twitches occur suddenly and often appear successively.
Iceberg
A piece of a glacier which has broken off and is floating in the sea.
Icelandic Low
A semi-permanent, subpolar area of low pressure in the North Atlantic Ocean. Because of its broad area and range of central pressure, it is an area where migratory lows tend to slow down and deepen. It is strongest during a Northern Hemisphere winter and early spring, centered over Iceland and southern Greenland, and is the dominate weather feature in the area. During the summer, it is weaker, less intense, and might divide into two parts, one west of Iceland, the other over the Davis Strait between Greenland and Baffin Island. Then the Azores or Bermuda High becomes the dominate weather feature in the North Atlantic.
Multicell Thunderstorm
These thunderstorms are organized in clusters of at least 2-4 short-lived cells. Each cell generates a cold air outflow and these individual outflows combine to form a large gust front. Convergence along the gust front causes new cells to develop every 5 to 15 minutes. The cells move roughly with the mean wind. However, the area (storm) motion usually deviates significantly from the mean wind due to discrete propagation (new cell development) along the gust front. The multicellular nature of the storm is usually apparent on radar with multiple reflectivity cores and maximum tops.
Office of Global Programs
The Office of Global Programs (OGP) sponsors focused scientific research, within approximately eleven research elements, aimed at understanding climate variability and its predictability. Through studies in these areas, researchers coordinate activities that jointly contribute to improved predictions and assessments of climate variability over a continuum of timescales from season to season, year to year, and over the course of a decade and beyond.
Orifice
In hydrologic terms,
(1) An opening with closed perimeter, usually sharp edged, and of regular form in a plate, wall, or partition through which water may flow, generally used for the purpose of measurement or control of water.
(2) The end of a small tube, such as a Pitot tube, piezometer, etc.
Pancake Ice
In hydrologic terms, circular flat pieces of ice with a raised rim; the shape and rim are due to repeated collisions
Pressure Ice
Floating sea, river, or lake ice that has been deformed, altered, or forced upward in pressure ridges by the lateral stresses of any combination of wind, water currents, tides, waves, and surf.
Ridge Ice
In hydrologic terms, ice piled haphazardly one piece over another in the form of ridges or walls.
Rime Ice
An opaque coating of tiny, white, granular ice particles caused by the rapid freezing of supercooled water droplets on impact with an object. See also clear ice.
River Ice Statement
A public product issued by the RFC containing narrative and numeric information on river ice conditions.
Rotten Ice
In hydrologic terms, ice in an advanced stage of disintegration.
Sea Ice
Any form of ice found at sea which has originated from the freezing of sea water (sea ice does NOT include superstructure icing). Ice formed from the freezing of the waters of the Great Lakes will be considered the same as sea ice.
Service Hydrologist
The designated expert of the hydrology program at a WFO.
Sheet ice
Ice formed by the freezing of liquid precipitation or the freezing of melted solid precipitation (see snow depth)
Shore ice
In hydrologic terms, an ice sheet in the form of a long border attached to the bank or shore.; border ice.
Snow Cornice
A mass of snow or ice projecting over a mountain ridge.
Solstice
Either of the two times per year when the sun is at its greatest angular distance from the celestial equator: about June 21 (the Northern Hemisphere summer solstice), when the sun reaches its northernmost point on the celestial sphere, or about December 22 (the Northern Hemisphere winter solstice), when it reaches its southernmost point.
Sublimation of ice
The transition of water from solid to gas without passing through the liquid phase.
Summer Solstice
The time at which the sun is farthest north in the Northern Hemisphere, on or around June 21.
Synthetic Aperture Radar River Ice Surveillance (SARRIS)
An experimental river ice mapping experiment using Synthetic Aperture Radar (SAR).
Weather Forecast Office
(Abbrev. WFO) - this type of National Weather Service office is responsible for issuing advisories, warnings, statements, and short term forecasts for its county warning area
Winter Solstice
The time at which the sun is farthest south in the Southern Hemisphere, on or around December 21.

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