Saturation
(of air) - the presence in air of
the most water possible under existent pressure
and temperature
Saturation
Vapor Pressure - see equilibrium
vapor pressure
Scattering
- the process by which small particles are forced to change
their direction of motion
Scud
(or Fractus) - small, ragged, low cloud fragments that are
unattached to a larger cloud base and often seen with and behind cold
fronts and thunderstorm gust fronts
Sea
Breeze - a cooling breeze blowing generally in the daytime
inland from the sea, caused by the temperature
difference when the sea surface is cooler than the adjacent land
Sea
Level Pressure - the atmospheric
pressure computed from the station pressure
for the given elevation of the station above mean
sea level
Sensible
Heat - the heat absorbed or transmitted
when the temperature of a substance changes
but the substance does not change state
Severe
Thunderstorm - a thunderstorm
with wind gusts of 50 knots (58 mph) or greater,
hail at least three-quarters of an inch in diameter,
and/or a tornado or funnel
cloud
Shear
- see wind shear
Shelf
Cloud - a low, horizontal wedge-shaped arcus
cloud, associated with a thunderstorm gust
front (or occasionally with a cold front,
even in the absence of thunderstorms).
Unlike the roll cloud, the shelf cloud
is attached to the base of the parent cloud above it (usually a thunderstorm).
Rising cloud motion often can be seen in the leading (outer) part of the
shelf cloud, while the underside often appears turbulent, boiling, and
wind-torn.
Shortwave
(or Shortwave Trough) - a disturbance in the middle or upper
part of the atmosphere which induces upward
motion ahead of it
Shortwave
Radiation - in meteorology, radiation
having a wavelength equal to or less than that of visible light
Shower
- intermittent precipitation
from a convective cloud, generally of short
duration
Sky
Cover - a term used to describe the amount of sky covered or
concealed by clouds or obscuring
phenomena. Classifications for sky cover include clear, broken,
partly cloudy, and overcast.
Sleet
- frozen or partly frozen falling rain;
ice pellets
Smog
- a natural fog made heavier and darker
by smoke and chemical fumes
Snow
- precipitation in the form
or small tabular and columnar white ice crystals
formed directly from the water vapor of
the air at a temperature of less than
0 degrees Celsius
Snow
Flurries - popular term for a light snow
shower
Snow
Pellets - precipitation
in the form of white, opaque, approximately round ice particles, about
2 to 5 mm in diameter, with a snow-like structure
Snow
Shower - intermittent snow falling from
a convective cloud
Snowflake
- a flake or crystal of snow
Solar
Radiation - the radiation emitted
by the sun
Solid
- one of the three basic phases of matter; a substance that
does not flow under moderate stress
Solstice
- the times of the year when the sun appears to the farthest
north or south of the equator, lying above either the Tropic of Cancer
or the Tropic of Capricorn
Sounding
- a plot of the vertical profile of temperature
and dew point (and often winds)
above a fixed location; used extensively in weather forecasting
Sounding-based
Stability Index - an index calculated from balloon
observations (e.g., CAPE, Lifted
Index, K-Index, Bulk Richardson Number,
Total-Totals Index) that provide guidance
about the potential organization, type, and severity of thunderstorms
(supercell, multi-cell,
etc.)
Southern
Oscillation - the reversal of typical surface air pressure
patterns across the tropical Pacific that occurs during a major El
Niño event
SPC
(Storm Prediction Center) -
a national forecast center in Norman, Oklahoma, which is part of
NCEP; responsible for providing short-term forecast
guidance for severe convection, excessive
rainfall (flash flooding), and severe
winter weather over the contiguous United States
Specific
Heat - the amount of heat required
to raise the temperature of 1 gram of
a substance by 1 degree Celsius
Specific
Volume - volume per unit mass; the reciprocal of density
Speed
Shear - the component of wind shear
resulting from a change in wind speed with height (e.g., southwesterly
winds of 20 mph at 10,000 feet increasing to 50 mph at 20,000 feet). Speed
shear is an important factor in severe weather development, especially
in the middle and upper levels of the atmosphere.
Splitting
Storm - a thunderstorm which
splits into two storms which follow diverging paths (a left
mover and a right mover). The left
mover typically moves faster than the original storm, the right mover,
slower. Of the two, the left mover is most likely to weaken and dissipate
(but on rare occasions can become a very severe anticyclonic-rotating
storm), while the right mover is the one most likely to reach supercell
status.
Squall
Line - any line or narrow band of active thunderstorms
which is not directly along a frontal boundary
Standard
Atmosphere - a hypothetical vertical distribution of atmospheric
temperature, pressure, and density
Standard
Atmospheric Pressure - the pressure
exerted by a 760 millimeter column of mercury at sea level at a temperature
of 0 degrees Celsius; equal to 1013.25 millibars
(mb), 29.92 inches of mercury (in of Hg), or 14.7 pounds per square inch
Stationary
Front - the boundary between two air
masses neither of which is replacing the other
Station
Model - the specific pattern for entering meteorological symbols
on a weather map that describe the state of
the weather at that geographical location
Station
Pressure - the actual pressure
measured at a given station location after being corrected for temperature,
gravity, and instrument error
Stefan-Boltzmann
Law - a mathematical relationship for electromagnetic
radiation that states the irrandiance
of a blackbody is proportional to the fourth
power of the absolute temperature of
the blackbody
Storm
- a disturbance of the atmosphere
marked by wind and usually by rain,
snow, hail, sleet,
or thunder and lightning
Storm
Centroid - the location of the center of a given storm. The
NEXRAD RPG runs a storm detection and tracking
algorithm to determine storm centroids
automatically for each volume scan
Storm-Relative
- measured relative to a moving thunderstorm,
usually referring to winds, wind
shear, or helicity
Storm-Relative
Velocity - the wind velocity minus storm motion. The wind at
a given location may be the combination of the environmental flow plus
winds due to a thunderstorm. NEXRAD
produces a storm-relative radial velocity
product from the base velocity product
by subtracting the average motion of all identified storms on the radar
scope.
Storm-Scale
- referring to weather systems with sizes on the order of individual
thunderstorms
Storm
Surge - an atypical rise of the sea along a shore primarily
resulting from the winds of a storm,
especially those of a hurricane
Straight-Line
Winds - generally, any wind that
is not associated with rotation, used mainly to differentiate them from
tornadic winds.
Stratiform
- having extensive horizontal development, as opposed to the
more vertical development characteristic of convection;
stratiform precipitation, in general, is relatively continuous and uniform
in intensity
Stratocumulus
- a low-level cloud in the form
of a gray and/or whitish flat layer or patch, which nearly always has
dark parts and is non-fibrous
Stratus
- a low-level cloud in the form
of a gray layer with a rather uniform base
Sublimation
- the process of changing from a solid
directly to vapor or gas
Subsidence
- sinking (downward) motion in the atmosphere, usually over
a broad area
Subtropical
High - a semi-permanent high pressure region near 30 degrees
latitude
Suction
Vortex (sometimes Suction Spot) - a small but very intense
vortex within a tornado circulation; much
of the extreme damage associated with violent tornadoes is attributed
to suction vortices.
Summer
- the period extending from the summer
solstice, about 21 June, to the autumnal
equinox, about 22 September
Summer
Solstice - the solstice when the sun
is highest in the sky; the first day of summer
Sundog
- a colored luminous spot appearing 22 degrees (or somewhat
more) on either side of the sun and at the same elevation as the sun
Sun
Pillar - a luminous streak of white or slightly reddened light
extending vertically above and below the sun, most frequently observed
near sunrise or sunset
Supercell
(or Supercell Storm) - a violent thunderstorm
which can produce hail and large tornadoes
and containing updrafts and downdrafts
that are nearly in balance, allowing it to maintain itself for several
hours
Synoptic
- relating to or displaying conditions as they exist simultaneously
over a broad area
Synoptic
Scale - the scale of the migratory high
and low pressure systems of the lower troposphere;
generally considered 1000 to 2500 km in length
|