Aeration Zone
A portion of the lithosphere in which the functional interstices of permeable rock or earth are not filled with water under hydrostatic pressure. The interstices either are not filled with water or are filled with water that is no held by capillarity.
Anvil Zits
Slang for frequent (often continuous or nearly continuous), localized lightning discharges occurring from within a thunderstorm anvil.
Azimuth
A direction in terms of a 360° compass. North is at 0°, east is at 90°, south is at 180°, and west is at 270°.
Azimuth Angle
The direction or bearing toward which a sloping surface faces (e.g., a north-facing slope has an azimuth angle of 360°; a northeast-facing slope, an azimuth angle of 45°).
Azores Current
One of the currents of the North Atlantic subtropical gyre.
Azores High
Alternate term for Bermuda High - a semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores in the eastern part of the North Atlantic. Also known as Azores High.
Baroclinic Zone
A region in which a temperature gradient exists on a constant pressure surface. Baroclinic zones are favored areas for strengthening and weakening systems; barotropic systems, on the other hand, do not exhibit significant changes in intensity. Also, wind shear is characteristic of a baroclinic zone.
Beginning of Freezup
In hydrologic terms, date on which ice forming a stable winter ice cover is first observed on the water surface
Blizzard
(abbrev. BLZD)- A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer:
Blizzard Warning
Issued for winter storms with sustained or frequent winds of 35 mph or higher with considerable falling and/or blowing snow that frequently reduces visibility to 1/4 of a mile or less. These conditions are expected to prevail for a minimum of 3 hours.
BLZD
Blizzard- A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer:
Breezy
15 to 25 mph winds
Capillary Zone
Used interchangably with Capillary Fringe; the soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches, to a few feet, and it depends on the pore sizes of the materials.
Channelization
In hydrologic terms, the modification of a natural river channel; may include deepening, widening, or straightening.
dBZ
Nondimensional "unit" of radar reflectivity which represents a logarithmic power ratio (in decibels, or dB) with respect to radar reflectivity factor, Z.
Deformation Zone
The change in shape of a fluid mass by variations in wind, specifically by stretching and/or shearing. Deformation is a primary factor in frontogenesis (evolution of fronts) and frontolysis (decay of fronts).
Drizzle
Precipitation consisting of numerous minute droplets of water less than 0.5 mm (500 micrometers) in diameter.
Drop-size Distribution
The distribution of rain drops or cloud droplets of specified sizes.
DZ
Drizzle
Entrainment Zone
A shallow region at the top of a convective boundary layer where fluid is entrained into the growing boundary layer from the overlying fluid by the collapse of rising convective plumes or bubbles.
Esturine Zone
In hydrologic terms, the area near the coastline that consists of esturaries and coastal saltwater wetlands
Flood Hazard Outlook (FHO)
An infographic which messages general flash and river flood hazards across the U.S. for the next seven days. It provides a general overview for regional and national decision makers.
Fracture Zone
In hydrologic terms, an area which has a great number of fractures.
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.
Frazil Slush
In hydrologic terms, an agglomerate of loosely packed frazil which floats or accumulates under the ice cover.
Freeze
A freeze is when the surface air temperature is expected to be 32°F or below over a widespread area for a climatologically significant period of time. Use of the term is usually restricted to advective situations or to occasions when wind or other conditions prevent frost. "Killing" may be used during the growing season when the temperature is expected to be low enough for a sufficient duration to kill all but the hardiest herbaceous crops.
Freeze Warning
Issued during the growing season when surface temperatures are expected to drop below freezing over a large area for an extended period of time, regardless whether or not frost develops.
Freezeup date
In hydrologic terms, the date on which the water body was first observed to be completely frozen over
Freezing Drizzle
A drizzle that falls as a liquid but freezes into glaze or rime upon contact with the cold ground or surface structures.
Freezing Drizzle Advisory
Issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems.
Freezing Fog
A fog the droplets of which freeze upon contact with exposed objects and form a coating of rime and/or glaze.
Freezing Level
The altitude at which the air temperature first drops below freezing.
Freezing Rain
Rain that falls as a liquid but freezes into glaze upon contact with the ground.
Freezing Rain Advisory
Issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems.
Freezing Spray
An accumulation of freezing water droplets on a vessel caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Freezing Spray Advisory
An advisory for an accumulation of freezing water droplets on a vessel at a rate of less than 2 centimeters (cm) per hour caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Freezup jam
In hydrologic terms, ice jam formed as frazil ice accumulates and thickens
Frozen Dew
When liquid dew changes into tiny beads of ice. This occurs when dew forms and temperatures later drop below freezing.
FRZ
Freeze
FRZN
Frozen
FZRA
freezing rain
Glaze
Ice formed by freezing precipitation covering the ground or exposed objects.
Great Lakes Freeze-Up/Break-Up Outlook
(FBO) - A National Weather Service product to keep mariners informed of the projected freeze-up date or break-up date of ice on the Great Lakes.
Ground Blizzard Warning
When blizzard conditions are solely caused by blowing and drifting snow.
Hail Size
Typically refers to the diameter of the hailstones. Warnings and reports may report hail size through comparisons with real-world objects that correspond to certain diameters:

DescriptionDiameter (inches)
Pea0.25
Marble or Mothball0.50
Penny or Dime0.75
Nickel0.88
Quarter1.00
Half Dollar1.25
Walnut or Ping Pong Ball1.50
Golfball1.75
Hen's Egg2.00
Tennis Ball2.50
Baseball2.75
Tea Cup3.00
Grapefruit4.00
Softball4.50
Hazardous Seas Warning
A warning for wave heights and/or wave steepness values meeting or exceeding locally defined warning criteria.
Hazardous Seas Watch
A watch for an increased risk of a hazardous seas warning event to meet Hazardous Seas Warning criteria but its occurrence, location, and/or timing is still uncertain.
Hazardous Weather Outlook
A narrative statement produced by the National Weather Service, frequently issued on a routine basis, to provide information regarding the potential of significant weather expected during the next 1 to 5 days.
Hazards Assessment
CPC's Hazards Assessment provides emergency managers, planners, forecasters and the public advance notice of potential hazards related to climate, weather and hydrological events.
Haze
(abbrev. HZ)- An aggregation in the atmosphere of very fine, widely dispersed, solid or liquid particles, or both, giving the air an opalescent appearance that subdues colors.
Heavy Freezing Spray
An accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Heavy Freezing Spray Warning
A warning for an accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Heavy Freezing Spray Watch
A watch for an increased risk of a heavy freezing spray event to meet Heavy Freezing Spray Warning criteria but its occurrence, location, and/or timing is still uncertain.
Hertz
(abbrev. Hz)- An international unit of frequency equal to one cycle per second, and named after a German physicist.
Horizon
The distant line along which the earth and sky appear to meet. Obstructions are not considered as part of the horizon.
HZ
1) Haze- An aggregation in the atmosphere of very fine, widely dispersed, solid or liquid particles, or both, giving the air an opalescent appearance that subdues colors.

(or)

2) Hertz- An international unit of frequency equal to one cycle per second, and named after a German physicist.
Intertropical Convergence Zone
(ITCZ) The region where the northeasterly and southeasterly trade winds converge, forming an often continuous band of clouds or thunderstorms near the equator.
ITCZ
Inter-tropical Convergence Zone. The region where the northeasterly and southeasterly tradewinds converge, forming an often continuous band of clouds or thunderstorms near the equator
Kelvin-Helmholtz Waves
Vertical waves in the air associated with wind shear across statically-stable regions. Can appear as breaking waves and as braided patterns in radar images and cloud photos.
Lake Breeze
A thermally produced wind blowing during the day from the surface of a large lake to the shore, caused by the difference in the rates of heating of the surfaces of the lake and of the land.
Land Breeze
A coastal breeze at night blowing from land to sea, caused by the difference in the rates of cooling of their respective surfaces.
Layered Haze
Haze produced when air pollution from multiple line, area or point sources is transported long distances to form distinguishable layers of discoloration in a stable atmosphere.
Littoral Zone
In hydrologic terms, the area on, or near the shore of a body water
Marine Zone
Specific, defined over-water areas contained in the various NWS marine forecasts. These are the equivalent of "zones" in the public forecast program.
Offshore Breeze
A wind that blows from the land towards a body of water. Also known as a land breeze.
Onshore Breeze
A wind that blows from a body of water towards the land. Also known as a seabreeze
Ozone
A form of oxygen, O3. A powerful oxidizing agent that is considered a pollutant in the lower troposphere but an essential chemical in the stratosphere where it protects the earth from high-energy ultraviolet radiation from the sun.
Ozone Action Day
A "heads-up" message issued by the Department of Natural Resources (DNR) through the National Weather Service when ozone levels may reach dangerous levels the next day. This message encourages residents to prevent air pollution by postponing the use of lawn mowing, motor vehicles, boats, as well as filling their vehicle gas tanks.
Ozone Advisory
It is issued by the Department of Natural Resources (DNR) through the National Weather Service when ozone levels reach 100. Ozone levels above 100 are unhealthy for people with heat and/or respiratory ailments.
Ozone Hole
A severe depletion of stratospheric ozone over Antarctica that occurs each spring. The possibility exists that a hole could form over the Arctic as well. The depletion is caused by a chemical reaction involving ozone and chlorine, primarily from human produced sources, cloud particles, and low temperatures.
Ozone Layer
An atmospheric layer that contains a high proportion of oxygen that exists as ozone. It acts as a filtering mechanism against incoming ultraviolet radiation. It is located between the troposphere and the stratosphere, around 9.5 to 12.5 miles (15 to 20 kilometers) above the earth's surface.
Pervious Zone
In hydrologic terms, a part of the cross section of an embankment dam comprising material of high permeability
Phiezometer
In hydrologic terms, an instrument used to measure pressure head in a conduit, tank, soil, etc. They are used in dams to measure the level of saturation.
Polarization Radar
A radar which takes advantage of ways in which the transmitted waves' polarization affect the backscattering. Such radars may alternately transmit horizontal and vertically polarized beams, and measure differential reflectivity.
Puget Sound Convergence Zone
A situation where wind forced around the Olympic Mountains converges over the Puget Sound. Causes extreme variability in weather conditions around Seattle, Washington with some areas of sunshine and others in clouds and rain.
Radar Reflectivity Factor (z)
z = the sum (over i) of (N_i * D_i^6), where N_i is the number of drops of diameter D_i in a pulse resolution volume. Note that z may be expressed in linear or logarithmic units. The radar reflectivity factor is simply a more meteorologically meaningful way of expressing the radar reflectivity.
Range Normalization
A receiver gain function in the radar which compensates for the effect of range (distance) on the received power for an equivalent reflectivity.
Regional Haze
Haze that is mixed uniformly between the surface and the top of a convective boundary layer.
Riparian Zone
In hydrologic terms, a stream and all the vegetation on its banks.
Sea Breeze
A thermally produced wind blowing during the day from a cool ocean surface onto the adjoining warm land, caused by the difference in the rates of heating of the surfaces of the ocean and of the land.
Sea Breeze Convergence Zone
The zone at the leading edge of a sea breeze where winds converge. The incoming air rises in this zone, often producing convective clouds.
Sea Breeze Front
The leading edge of a sea breeze, whose passage is often accompanied by showers, a wind shift, or a sudden drop in temperature.
Sectorized Hybrid Scan
A single reflectivity scan composed of data from the lowest four elevation scans. Close to the radar, higher tilts are used to reduce clutter. At further ranges, either the maximum values from the lowest two scans are used or the second scan values are used alone.
Small Craft Advisory for Hazardous Seas
(SCAHS) - An advisory for wind speeds lower than small craft advisory criteria, yet waves or seas are potentially hazardous due to wave height, wave period, steepness, or swell direction. Thresholds governing the issuance of Small Craft Advisories for Hazardous Seas are specific to geographic areas. * Eastern (ME..SC, Lake Erie, Lake Ontario) - Seas or waves 5 to 7 feet and greater, area dependent. * Central (MN..OH) - Seas or waves greater than 4 feet * Southern (GA..TX and Caribbean) - Seas 7 feet or greater that are expected for more than 2 hours. * Western (WA..CA) - Criteria for wave heights and/or wave steepness are locally defined; refer to Western Region Supplement 12-2003, Marine Weather Services. * Alaska (AK) - Seas or wave conditions deemed locally significant, based on user needs, and should be no lower than 8 feet. * Pacific - (HI, Guam, etc) - Seas of 10 feet or greater.
St Lawrence Freeze-Up Outlook
A National Weather Service forecast product to keep mariners informed of the projected freeze-up date of ice the St. Lawrence River.
Stratospheric Ozone
In the stratosphere, ozone has beneficial properties where it forms an ozone shield that prevents dangerous radiation from reaching the Earth's surface. Recently, it was discovered that in certain parts of the world, especially over the poles, stratospheric ozone was disappearing creating an ozone hole.
Surf Zone
Area of water between the high tide level on the beach and the seaward side of the breaking waves.
Surf Zone Forecast
(SRF) - A National Weather Service routine or event driven forecast product geared toward non-boating marine users issued for an area extending from the area of water between the high tide level on the beach and the seaward side of the breaking waves.
Syzygy
In solar-terrestrial terms, the instance (new moon or full moon) when the earth, sun, and moon are all in a straight line.
Vadose Zone
The locus of points just above the water table where soil pores may either contain air or water. This is also called the zone of aeration
Velocity Azimuth Display
A WSR 88-D product which shows the radar derived wind speeds at various heights. This radar product shows the wind speeds from 2,000 to 55,000 feet above the ground. VAD and EVAD (Extended VAD) are methods of guessing the large scale two-dimensional winds from one-dimensional radial velocity data. They are essentially multivariate regressions which fit a simple, large scale wind model to the observed winds. EVAD also estimates the large scale horizontal divergence and particle fall speed. See VWP.
Velocity Zones
In hydrologic terms, areas within the floodplain subject to potential high damage from waves. These sometimes appear on flood insurance rate maps
WBZ
Wet Bulb Zero - the height where the wet-bulb temperature goes below 0°C. It is important because WBZ heights between 7000 ft and 10,500 ft (above ground level) correlate well with large hail at the surface when storms develop in an airmass primed for strong convection. Higher values infer mid and upper level stability and also indicate a large melting area for falling hail. Lower WBZ heights indicate that the low level atmosphere is often too cool and stable to support large hail.
Wet Bulb Zero
(Abbrev. WBZ) - the height where the wet-bulb temperature goes below 0°C. It is important because WBZ heights between 7000 ft and 10,500 ft (above ground level) correlate well with large hail at the surface when storms develop in an airmass primed for strong convection. Higher values infer mid and upper level stability and also indicate a large melting area for falling hail. Lower WBZ heights indicate that the low level atmosphere is often too cool and stable to support large hail.
Z
Zulu time; the same as Universal Coordinated Time (UTC), i.e. 18z is the same as 18:00 UTC.
Zero Datum
In hydrologic terms, a reference "zero" elevation for a stream or river gage. This "zero" can be referenced (usually within ten feet of the bottom of the channel) to mean sea level, or to any other recognized datum.
ZFP
Zone Forecast Product
ZL
Freezing Drizzle
ZNS
zones
Zonal Flow
Large-scale atmospheric flow in which the east-west component (i.e., latitudinal) is dominant. The accompanying meridional (north-south) component often is weaker than normal. Compare with meridional flow.
Zone of Aeration
In hydrologic terms, the locus of points just above the water table where soil pores may either contain air or water. This is also called the vadose zone
Zone of Saturation
In hydrologic terms, the locus of points below the water table where soil pores are filled with water. This is also called the phreatic zone
Zoned Embankment Dam
In hydrologic terms, an embankment dam which is comprised of zones of selected materials having different degrees of porosity, permeability and density.
ZR
Freezing Rain
Zulu (Z) Time
For practical purposes, the same as Coordinated Universal Time (UTC). The notation formerly used to identify time Greenwich MeanTime. The word "Zulu" is notation in the phonetic alphabet corresponding to the letter "Z" assigned to the time zone on the Greenwich Prime Meridian.
Zurich Sunspot Classification
In solar-terrestrial terms, a sunspot classification system that has been modified for SESC use.
Z\/R Relationship
An empirical relationship between radar reflectivity factor z (in mm^6 / m^3 ) and rain rate ( in mm / hr ), usually expressed as Z = A R^b; A and b are empirical constants.

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