Subj : Wx Terms (R)(3)
To   : All
From : Daryl Stout
Date : Sun Nov 19 2017 12:05 am

Red Watch or Red Box
Slang for Tornado Watch.

REF
Reference

Reference Mark
A relatively permanent point of known elevation which is tied to a
benchmark.

Reflection
The process whereby radiation (or other waves) incident upon a surface is
directed back into the medium through which it traveled.

Reflectivity
Usually a reference to Radar Reflectivity; the sum of all backscattering
cross-sections (e.g., precipitation particles) in a pulse resolution
volume divided by that volume. The radar reflectivity can be related to
the radar reflectivity factor through the dielectric constant term
|K|^2, and the radar wavelength.

Reflectivity Cross Section
This WSR-88D radar product displays a vertical cross section of
reflectivity on a grid with heights up to 70,000 feet on the vertical
axis and distance up to 124 nm on the horizontal axis. Cross Section is
similar to the Range Height Indicator (RHI) slices observed on
conventional radar, but it is not limited to alignments along the radar
radials. Instead the 2 end points are operator selected anywhere within
124 nm of the radar that are less than 124 nm apart. It is used to:

1) Examine storm structure features such as overhang, tilt, Weak Echo
Regions (WER), and Bounded Weak Echo Regions (BWER);

2) Estimate height of higher dBZ's and echo tops; and

3) Locate the bright band (where snow is melting and becoming rain).

Reflectivity Factor
The result of a mathematical equation (called the Weather Radar
Equation) that converts the analog power (in Watts) received by the
radar antenna into a more usable quantity. The reflectivity factor
(denoted by Z) takes into account several factors, including the
distance of a target from the radar, the wavelength of the transmitted
radiation, and certain assumptions about the kind and size of targets
detected by the radar. The reflectivity factor ranges over several
orders of magnitudes, so it is usually expressed on a logarithmic scale
called dBZ (decibels of reflectivity).

Refraction
Changes in the direction of energy propagation as a result of density
changes within the propagating medium. In weather terms, this is
important on determining how a radar beam reacts in the atmosphere.

Refractive Index
A measure of the amount of refraction. Numerically equal to the ratio
of wave velocity in a vacuum to a wave speed in the medium, i.e.,
n = c / v where: v is actual speed, and c is speed of light in a vacuum.

Refractivity
Expressed as N; N = (n-1)*106, where n is refractive index and N is a
function of temperature, pressure and vapor pressure (in the atmosphere).

Regional Haze
Haze that is mixed uniformly between the surface and the top of a
convective boundary layer.

Relative Humidity
A dimensionless ratio, expressed in percent, of the amount of
atmospheric moisture present relative to the amount that would be
present if the air were saturated. Since the latter amount is dependent
on temperature, relative humidity is a function of both moisture content
and temperature. As such, relative humidity by itself does not directly
indicate the actual amount of atmospheric moisture present. See dew point.

Relative Vorticity
The sum of the rotation of an air parcel about the axis of the pressure
system and the rotation of the parcel about its own axis.

Relative Wind
The wind with reference to a moving point. Sometimes called APPARENT WIND.
See also APPARENT WIND, TRUE WIND.

RELBL
Reliable

Relocated
A term used in an advisory to indicate that a vector drawn from the
preceding advisory position to the latest known position is not
necessarily a reasonable representation of the cyclone's movement.

Remote Observing System Automation
A type of automated data transmitter used by NWS Cooperative Program
observers.

REP
Represent/Representative

Report
A weather report is a statement of the actual weather conditions
observed at a specific time at a specific site.

Reservoir
In hydrologic terms, a manmade facility for the storage, regulation
and controlled release of water.

Residual Layer
The elevated portion of a convective boundary layer that remains after
a stable boundary layer develops at the ground (usually in late
afternoon or early evening) and cuts off convection.

Residual Moisture
Atmospheric moisture which lingers over an area after the main weather
system has departed.

Resonance
The state of a system in which an abnormally large vibration is produced
in response to an external stimulus, occurring when the frequency of
the stimulus is the same, or nearly the same, as the natural vibration
frequency of the system.

Response Time
In hydrologic terms, the amount of time in which it will take a
watershed to react to a given rainfall event.

Retrogression
(or Retrograde Motion) - Movement of a weather system in a direction
opposite to that of the basic flow in which it is embedded, usually
referring to a closed low or a longwave trough which moves westward.

Return Flow
South winds on the back (west) side of an eastward-moving surface high
pressure system. Return flow over the central and eastern United States
typically results in a return of moist air from the Gulf of Mexico (or
the Atlantic Ocean).

Return Stroke
An electrical discharge that propagates upward along a lightning
channel from the ground to the cloud.

Rex Block
A blocking pattern where there is an upper level high located directly
north of a closed low.

RFC
River Forecast Center. Centers that serve groups of Weather Service
Forecast offices and Weather Forecast offices, in providing hydrologic
guidance and is the first echelon office for the preparation of river
and flood forecasts and warnings.

RGD
Ragged

RGN
Region

RH
Relative Humidity - a dimensionless ratio, expressed in percent, of
the amount of atmospheric moisture present relative to the amount that
would be present if the air were saturated. Since the latter amount is
dependent on temperature, relative humidity is a function of both
moisture content and temperature. As such, relative humidity by itself
does not directly indicate the actual amount of atmospheric moisture
present. See dew point.

RHI
Range-Height Indicator

Ribbon Lightning
Appears to be a broad stream of fire. A succession of strokes, each blown
a bit to the side of the previous strokes by wind, but striking so fast
that all the strokes are seen at once as a ribbon-like flash.

Ridge

1) An elongated area of relatively high atmospheric pressure; the opposite
of trough.
or

2) In hydrologic terms, a line or wall of broken ice forced up by
pressure. May be fresh or weathered.

Ridge Ice
In hydrologic terms, ice piled haphazardly one piece over another in the
form of ridges or walls.

Right Ascension
The celestial longitude of the sun. This value is 0 at the vernal equinox,
90 at the summer solstice, 180 at the autumnal equinox and 270 at the
winter solstice.

Right Entrance Region
Used interchangably with Right Rear Quadrant; the area upstream from and
to the right of an upper-level jet max (as would be viewed looking along
the direction of flow). Upward motion and severe thunderstorm potential
sometimes are increased in this area relative to the wind speed maximum.
See also exit region, left front quadrant.



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