Subj : Wx Terms (S)(2)
To   : All
From : Daryl Stout
Date : Sun Aug 20 2017 12:04 am

Secondary Pollutant
Pollutants generated by chemical reactions occurring within the
atmosphere. Compare primary pollutant.

Sector Boundary
In solar-terrestrial terms, in the solar wind, the area of demarcation
between sectors, which are large-scale features distinguished by the
predominant direction of the interplanetary magnetic field, toward or
away from the sun.

Sector Visibility
The visibility in a specific direction that represents at least a 45�
arc of a horizontal circle.

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.

Securite
A headline within National Weather Service high seas forecasts transmitted
via the GMDSS to indicate that no hurricane or hurricane force winds are
forecast.

Sediment Storage Capacity
In hydrologic terms, the volume of a reservoir planned for the deposition
of sediment.

Seepage
In hydrologic terms, the interstitial movement of water that may take
place through a dam, its foundation, or abutments.

Seiche
A standing wave oscillation of water in large lakes usually created by
strong winds and/or a large barometric pressure gradient.

SEL
A watch cancellation statement issued to terminate a watch before its
original expiration time.

SELS
Severe Local Storm

SELY
Southeasterly

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.

Separation Eddy
An eddy that forms near the ground on the windward or leeward side of a
bluff object or steeply rising hillside; streamlines above this eddy go
over the object.

Serial Derecho
Type of derecho that consists of an extensive squall line which is
oriented such that the angle between the mean wind direction and the
squall line axis is small. A series of LEWPs and bow echoes move along
the line. The downburst activity is associated with the LEWPs and bows.
A Serial Derecho tends to be more frequent toward the north end of the
line during the late winter and spring months. It occurs less
frequently than its cousin the "progressive derecho."

It is associated with a linear type mesoscale convective system that
moves along and in advance of a cold front or dry line. These boundaries
are often associated with a strong, migratory surface low pressure
system and strong short wave trough at 500 mb (strong dynamic forcing).
Lifted Indices are typically -6 or lower and the advection of dry air
in the mid-troposphere (3-7 km above ground) by relatively strong winds
leads to high convective instability and increased downdraft potential.
The bow echoes move along the line in the direction of the mean flow,
often southwest to northeast. These storms move at speeds exceeding 35
knots. Squall line movement is often less than 30 knots.

SERN
Southeastern

Service Hydrologist
The designated expert of the hydrology program at a WFO.

Servo Loop
In radar meteorology, a generic description of hardware needed to
remotely control the motion of the antenna dish.

Set
The direction towards which a current is headed. For example, a current
moving from west to east is said to be set to east.

Set-up
The process whereby strong winds blowing down the length of a lake cause
water to "pile up" at the downwind end, raising water levels there and
lowering them at the upwind end of the lake.

Severe Icing
The rate of ice accumulation on an aircraft is such that
de-icing/anti-icing equipment fails to reduce or control the hazard.
Immediate diversion is necessary.

Severe Local Storm
A convective storm that usually covers a relatively small geographic
area, or moves in a narrow path, and is sufficiently intense to threaten
life and/or property. Examples include severe thunderstorms with large
hail, damaging wind, or tornadoes. Although cloud-to-ground lightning is
not a criteria for severe local storms, it is acknowledged to be highly
dangerous and a leading cause of deaths, injuries, and damage from
thunderstorms. A thunderstorm need not be severe to generate frequent
cloud-to-ground lightning. Additionally, excessive localized convective
rains are not classified as severe storms but often are the product of
severe local storms. Such rainfall may result in related phenomena
(flash floods) that threaten life and property.

Severe Local Storm Watch
An alert issued by the National Weather Service for the contiguous U.S.
and its adjacent waters of the potential for severe thunderstorms or
tornadoes.

Severe Thunderstorm
A thunderstorm that produces a tornado, winds of at least 58 mph
(50 knots), and/or hail at least 3/4" in diameter. Structural wind damage
may imply the occurrence of a severe thunderstorm. A thunderstorm wind
equal to or greater than 40 mph (35 knots) and/or hail of at least 1/2"
is defined as approaching severe.

Severe Thunderstorm Warning
This is issued when either a severe thunderstorm is indicated by the
WSR-88D radar or a spotter reports a thunderstorm producing hail 3/4 inch
or larger in diameter and/or winds equal or exceed 58 miles an hour;
therefore, people in the affected area should seek safe shelter
immediately. Severe thunderstorms can produce tornadoes with little or no
advance warning. Lightning frequency is not a criteria for issuing a
severe thunderstorm warning. They are usually issued for a duration of
one hour. They can be issued without a Severe Thunderstorm Watch being
already in effect.

Like a Tornado Warning, the Severe Thunderstorm Warning is issued by
your National Weather Service Forecast Office (NWFO). Severe Thunderstorm
Warnings will include where the storm was located, what towns will be
affected by the severe thunderstorm, and the primary threat associated
with the severe thunderstorm warning. If the severe thunderstorm will
affect the nearshore or coastal waters, it will be issued as the combined
product--Severe Thunderstorm Warning and Special Marine Warning. If the
severe thunderstorm is also causing torrential rains, this warning may
also be combined with a Flash Flood Warning. If there is an ampersand
(&) symbol at the bottom of the warning, it indicates that the warning
was issued as a result of a severe weather report.

After it has been issued, the affected NWFO will follow it up
periodically with Severe Weather Statements. These statements will
contain updated information on the severe thunderstorm and they will
also let the public know when the warning is no longer in effect.

Severe Thunderstorm Watch
This is issued by the National Weather Service when conditions are
favorable for the development of severe thunderstorms in and close to
the watch area. A severe thunderstorm by definition is a thunderstorm
that produces 3/4 inch hail or larger in diameter and/or winds equal or
exceed 58 miles an hour. The size of the watch can vary depending on the
weather situation. They are usually issued for a duration of 4 to 8
hours. They are normally issued well in advance of the actual occurrence
of severe weather. During the watch, people should review severe
thunderstorm safety rules and be prepared to move a place of safety if
threatening weather approaches.

A Severe Thunderstorm Watch is issued by the Storm Prediction Center in
Norman, Oklahoma. Prior to the issuance of a Severe Thunderstorm Watch,
SPC will usually contact the affected local National Weather Service
Forecast Office (NWFO) and they will discuss what their current thinking
is on the weather situation. Afterwards, SPC will issue a preliminary
Severe Thunderstorm Watch and then the affected NWFO will then adjust
the watch (adding or eliminating counties/parishes) and then issue it
to the public by way of a Watch Redefining Statement. During the watch,
the NWFO will keep the public informed on what is happening in the
watch area and also let the public know when the watch has expired or
been cancelled.

Severe Weather Analysis
This WSR-88D radar product provides 3 base products (reflectivity (SWR),
radial velocity (SWV), and spectrum width (SWW)) at the highest
resolution available along with radial shear (SWS). These products are
mapped into a 27 nm by 27 nm region centered on a point which the
operator can specify anywhere within a 124 nm radius of the radar. It
is most effective when employed as an alert paired product with the
product centered on alert at height that caused the alert. It is used
to examine 3 base products simultaneously in a 4 quadrant display; and
analyze reflectivity and velocity products at various heights to gain a
comprehensive vertical analysis of the thunderstorm.

Severe Weather Potential Statement
This statement is designed to alert the public and state/local agencies
to the potential for severe weather up to 24 hours in advance. It is
issued by the local National Weather Service office.

Severe Weather Probability
This WSR-88D radar product algorithm displays numerical values
proportional to the probability that a storm will produce severe
weather within 30 minutes. Values determined using a statistical
regression equation which analyzes output from the VIL algorithm. It
is used to quickly identify the most significant thunderstorms.



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