Ablation
Depletion of snow and ice by melting and evaporation.
Absolutely Stable Air
An atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic lapse rate.
Absolutely Unstable Air
An atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic lapse rate.
ADAPTATION (ADAPTABLE) PARAMETER
Generally, data related to a specific WSR-88D unit. These data may consist of meteorological or hydrological parameters or of geographic boundaries, political boundaries, system configuration, telephone numbers (auto dial), or other like data. Such data may be generated at either a centralized location or locally at the WSR-88D unit.
Air Transportable Mobile Unit
A modularized transportable unit containing communications and observational equipment necessary to support a meteorologist preparing on-site forecasts at a wildfire or other incident.
AVBL
Available
BL
Abbreviation for Boundary Layer; a layer of air adjacent to a bounding surface. Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected by daytime insolation and nighttime radiational cooling, and winds are affected by friction with the earth's surface. The effects of friction die out gradually with height, so the "top" of this layer cannot be defined exactly.
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.
Blackbody
A hypothetical "body" that absorbs all of the electromagnetic radiation striking it - it does not reflect or transmit any of the incident radiation. A blackbody not only absorbs all wavelengths, but emits at all wavelengths with the maximum possible intensity for any given temperature.
Blackbody Radiation
The electromagnetic radiation emitted by an ideal blackbody adhering to the radiation laws; it is the theoretical maximum amount of electromagnetic radiation of all wavelengths that can be emitted by a body at a given temperature.
BLD
Build
BLDUP
Buildup
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.
BLO
Below
Blocked Flow
Flow approaching a mountain barrier that is too weak or too stable to be carried over the barrier.
Blowing
A descriptor used to amplify observed weather phenomena whenever the phenomena are raised to a height of 6 feet or more above the ground
Blowing Dust or Sand
Strong winds over dry ground, that has little or no vegetation, can lift particles of dust or sand into the air. These airborne particles can reduce visibility, cause respiratory problems, and have an abrasive affect on machinery. A concentration reducing the visibility to ¼ mile or less often poses hazards for travelers.
Blowing Snow
Blowing snow is wind-driven snow that reduces surface visibility. Blowing snow can be falling snow or snow that has already accumulated but is picked up and blown by strong winds. Blowing snow is usually accompanied by drifting snow.
Blowing Snow Advisory
Issued when wind driven snow reduces surface visibility, possibly, hampering traveling. Blowing snow may be falling snow, or snow that has already accumulated but is picked up and blown by strong winds.
Blue Watch or Blue Box
[Slang], a severe thunderstorm watch.
Blustery
Same as Breezy; 15 to 25 mph winds.
BLV
before
BLZD
Blizzard- A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer:
Bubble High
A mesoscale area of high pressure, typically associated with cooler air from the rainy downdraft area of a thunderstorm or a complex of thunderstorms. A gust front or outflow boundary separates a bubble high from the surrounding air.
Bubbler Gage
In hydrologic terms, a water stage recording device that is capable of attaching to a LARC for data automation purposes.
Conditionally Unstable Air
An atmospheric condition that exists when the environmental lapse rate is less than the dry adiabatic lapse rate but greater than the moist adiabatic lapse rate.
CSDRBL
Considerable
Diablo Wind
Similar to Santa Ana winds in southern California. These winds occur below canyons in the East Bay hills (Diablo range) and in extreme cases can exceed 60 mph. They develop due to high pressure over Nevada and lower pressure along the central California coast.
Discharge Table
In hydrologic terms,

1. A table showing the relation between two mutually dependant quantities or variable over a given range of magnitude.

2. A table showing the relation between the gage height and the discharge of a stream or conduit at a given gaging station. Also called a Rating Table.
ENSEMBLE
A collection of numerical model results that show slightly different possible outcomes.
Ensemble Forecast
Multiple predictions from an ensemble of slightly different initial conditions and/or various versions of models. The objectives are to improve the accuracy of the forecast through averaging the various forecasts, which eliminates non-predictable components, and to provide reliable information on forecast uncertainties from the diversity amongst ensemble members. Forecasters use this tool to measure the likelihood of a forecast.
Ensemble Hydrologic Forecasting
In hydrologic terms, a process whereby a continuous hydrologic model is successively executed several times for the same forecast period by use of varied data input scenarios, or a perturbation of a key variable state for each model run. A common method employed to obtain a varied data input scenario is to use the historical meteorological record, with the assumption that several years of observed data covering the time period beginning on the current date and extending through the forecast period comprises a reasonable estimate of the possible range of future conditions.
Ensembles
Reference to a set of computer models run under the concept of Ensemble Forecasting: multiple predictions from an ensemble of models with slightly different initial conditions used as input and/or slightly different versions of models. The objectives are to improve the accuracy of the forecast through averaging the various forecasts, which eliminates non-predictable components, and to provide reliable information on forecast uncertainties from the diversity amongst ensemble members. Forecasters use this tool to measure the likelihood of a forecast.
Flash Flood Table
In hydrologic terms, a table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts. Soil moisture conditions are often represented by flash flood guidance values. In lieu of crest stages, categorical representations of flooding, e.g., minor, moderate, etc. may be used on the tables.
Flood Problems
In hydrologic terms, problems and damages that occur during a flood as a result of human development and actions. Flood problems are a result from:
1) Inappropriate development in the floodplain (e.g., building too low, too close to the channel, or blocking flood flows);
2) Development in the watershed that increases flood flows and creates a larger floodplain, or;
3) A combination of the previous two.
Global Ensemble Forecast System (GEFS)
A weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which are used to initialize weather forecast models.
Ground Blizzard Warning
When blizzard conditions are solely caused by blowing and drifting snow.
High Resolution Ensemble Forecast (HREF)
An ensemble of products from several different models running at ~3 km horizontal grid spacing.
Hydrologic Ensemble Forecast System (HEFS)
A probabilistic forecast tool with the goals to provide hydrologic forecasts including an analysis of “probable outcomes” and to minimize biases in the atmospheric models and in the hydrologic models.
Impermeable
Material that does not permit fluids to pass through it.
Intangible Flood Damage
In hydrologic terms, estimates of the damage done by disruption of business, danger to health, shock, and loss of life and in general all costs not directly measurable which require a large element of judgment for estimating.
Meteorological Model Ensemble River Forecast (MMEFS)
An automated short-term hydrologic ensemble forecast system which utilizes temperature and precipitation output from the National Centers for Environmental Prediction (NCEP) GEFS and NAEFS meteorological models as inputs to River Forecast Center hydrologic models.
Minimum Discernible Signal
In a receiver, it is the smallest input signal that will a produce a detectable signal at the output. In radar terms, it is the minimal amount of back scattered energy that is required to produce a target on the radar screen. In other words, MDS is a measure of the radar's sensitivity.
Movable Bed
In hydrologic terms, a stream bed made up of materials readily transportable by the stream flow
National Blend of Models (NBM)
The National Blend of Models (NBM) is a nationally consistent and skillful suite of calibrated forecast guidance based on a blend of both NWS and non-NWS numerical weather prediction model data and post-processed model guidance.
North American Ensemble Forecast System (NAEFS)
An atmospheric ensemble of 20 members each from the NCEP GEFS and CMC EPS ensemble systems.
PBL
Probable
Plume Blight
Visibility impairment caused by air pollution plumes aggregated from individual sources.
PRBLTY
Probability
PRBLY
probably
Precipitable Water
Measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given location, usually extending from the surface to 300 mb.
PSBL
Possible
PSBLY
possibly
Public Information Statement
A narrative statement issued by a National Weather Service Forecast Office that can be used for:

1) A current or expected nonhazardous event of general interest to the public that can usually be covered with a single message (e.g., unusual atmospheric phenomena such as sun dogs, halos, rainbows, aurora borealis, lenticular clouds, and stories about a long-term dry/cold/wet/warm spell).

2) Public educational information and activities, such as storm safety rules, awareness activities, storm drills, etc.

3) Information regarding service changes, service limitations, interruptions due to reduced or lost power or equipment outages, or special information clarifying interpretation of NWS data. For example, this product may be used to inform users of radar equipment outages or special information clarifying interpretation of radar data originating from an unusual source which may be mistaken for precipitation (such as chaff drops, smoke plumes, etc., that produces echoes on the radar display.
Public Severe Weather Outlook
These are issued when the Storm Prediction Center (SPC) in Norman, Oklahoma anticipates an especially significant and/or widespread outbreak of severe weather. This outlook will stress the seriousness of the situation, defines the threat area, and provides information on the timing of the outbreak. The lead time on this outlook is normally less than 36 hours prior to the severe weather event.
RELBL
Reliable
Rex Block
A blocking pattern where there is an upper level high located directly north of a closed low.
Sensible Heat Flux
The flux of heat from the earth's surface to the atmosphere that is not associated with phase changes of water; a component of the surface energy budget.
Snow Accumulation and Ablation Model
In hydrologic terms, a model which simulates snow pack accumulation, heat exchange at the air-snow interface, areal extent of snow cover, heat storage within the snow pack, liquid water retention, and transmission and heat exchange at the ground-snow interface.
Stable
An atmospheric state with warm air above cold air which inhibits the vertical movement of air.
Stable Boundary Layer
The stably-stratified layer that forms at the surface and grows upward, usually at night or in winter, as heat is extracted from the atmosphere's base in response to longwave radiative heat loss from the ground. Stable boundary layers can also form when warm air is advected over a cold surface or over melting ice.
Stable Core
Post-sunrise, elevated remnant of the temperature inversion that has built up overnight within a valley.
STBL
Stable
Sublimation
The transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase. Thus an ice crystal or icicle sublimes under low relative humidity at temperatures below 0°C. The process is analogous to evaporation of a liquid.
Sublimation of ice
The transition of water from solid to gas without passing through the liquid phase.
Symmetric Double Eye
A concentrated ring of convection that develops outside the eye wall in symmetric, mature hurricanes. The ring then propagates inward and leads to a double-eye. Eventually, the inner eye wall dissipates while the outer intensifies and moves inward.
UNSBL
Unseasonable
Unstable Air
Air that is able to rise easily, and has the potential to produce clouds, rain, and thunderstorms.
UNSTBL
Unstable
Variable Infiltration Capacity (VIC)
A large-scale, semi-distributed hydrologic model that solves full water and energy balances. As such, it shares several basic features with other land surface models that are commonly coupled to global circulation models.
Variable Wind
Same as Variable Wind Direction; a condition when
(1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or
(2) the direction is variable and the wind speed is less than 6 knots.
Variable Wind Direction
A condition when
(1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or
(2) the direction is variable and the wind speed is less than 6 knots.
Visible Infra-Red Imaging Radiometer (VIIRS)
A medium-resolution sensor flown aboard the NOAA-20 and Suomi-NP satellites.
Visible Satellite Imagery
This type of satellite imagery uses reflected sunlight (this is actually reflected solar radiation) to see things in the atmosphere and on the Earth's surface. Clouds and fresh snow are excellent reflectors, so they appear white on the imagery. Clouds can be distinguished from snow, because clouds move and snow does not move. Meanwhile, the ground reflects less sunlight, so it appears black on the imagery. The satellite uses its 0.55 to 0.75 micrometer (um) channel to detect this reflected sunlight. Since this imagery relies on reflected imagery, it cannot be used during night.
Water Table
The level below the earth's surface at which the ground becomes saturated with water. The water table is set where hydrostatic pressure equals atmospheric pressure.

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