|Glossay, Terms and definitions for storm spotters.
Severe weather definitions here.
NOAA Technical Memorandum NWS SR-145 Michael
Branick NOAA/WFO Norman
The information below is from NOAA's NWS Glossary and is their expertise and work that has
made this section available. It is provided here to give you accurate and professional
(C-H) Glossary (A-B) Glossary
(C-H) Glossary (I-R) Glossary
CA - Cloud-to-Air lightning.
Cap (or Capping Inversion) - A layer of relatively warm air aloft (usually several
thousand feet above the ground) which suppresses or delays the development of
thunderstorms. Air parcels rising into this layer become cooler than the surrounding air,
which inhibits their ability to rise further. As such, the cap often prevents or delays
thunderstorm development even in the presence of extreme instability. However if the cap
is removed or weakened, then explosive thunderstorm development can occur. See CIN,
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to
separate warm, moist air below and cooler, drier air above. With the cap in place, air
below it can continue to warm and/or moisten, thus increasing the amount of potential
instability. Or, air above it can cool, which also increases potential instability. But
without a cap, either process (warming/moistening at low levels or cooling aloft) results
in a faster release of available instability - often before instability levels become
large enough to support severe weather development.
CAPE - Convective Available Potential Energy. A measure of the amount of energy available
for convection. CAPE is directly related to the maximum potential vertical speed within an
updraft; thus, higher values indicate greater potential for severe weather. Observed
values in thunderstorm environments often may exceed 1,000 joules per kilogram (j/kg), and
in extreme cases may exceed 5,000 j/kg. However, as with other indices or indicators,
there are no threshold values above which severe weather becomes imminent. CAPE is
represented on a sounding by the area enclosed between the environmental temperature
profile and the path of a rising air parcel, over the layer within which the latter is
warmer than the former. (This area often is called positive area.) See also CIN. For more on CAPE read this.
*Cb - Cumulonimbus cloud, characterized by strong vertical development in the form of
mountains or huge towers topped at least partially by a smooth, flat, often fibrous anvil.
Also known colloquially as a "thunderhead."
CC - Cloud-to-Cloud lightning.
Cell - Convection in the form of a single updraft, downdraft, or updraft/downdraft
couplet, typically seen as a vertical dome or tower as in a cumulus or towering cumulus
cloud. A typical thunderstorm consists of several cells (see multi-cellular thunderstorm).
The term "cell" also is used to describe the radar echo returned by an
individual shower or thunderstorm. Such usage, although common, is technically incorrect.
*CG - Cloud-to-Ground lightning flash.
Chaff - Small strips of metal foil, usually dropped in large quantities from aircraft or
balloons. Chaff typically produces a radar echo which closely resembles precipitation.
Chaff drops once were conducted by the military in order to confuse enemy radar, but now
are conducted mainly for radar testing and calibration purposes.
CIN - Convective INhibition. A measure of the amount of energy needed in order to initiate
convection. Values of CIN typically reflect the strength of the cap.
They are obtained on a sounding by computing the area enclosed
between the environmental temperature profile and the path of a
rising air parcel, over the layer within which the latter is cooler
than the former. (This area sometimes is called negative area.) See
CAPE classroom study.
Cirrus - High-level clouds (16,000 feet or more), composed of ice crystals and appearing
in the form of white, delicate filaments or white or mostly white patches or narrow bands.
Cirrus clouds typically have a fibrous or hairlike appearance, and often are
semi-transparent. Thunderstorm anvils are a form of cirrus cloud, but most cirrus clouds
are not associated with thunderstorms.
Classic Supercell - See supercell.
Clear Slot - A local region of clearing skies or reduced cloud cover, indicating an
intrusion of drier air; often seen as a bright area with higher cloud bases on the west or
southwest side of a wall cloud. A clear slot is believed to be a visual indication of a
rear flank downdraft.
Closed Low - A low pressure area with a distinct center of cyclonic circulation which can
be completely encircled by one or more isobars or height contour lines. The term usually
is used to distinguish a low pressure area aloft from a low-pressure trough. Closed lows
aloft typically are partially or completely detached from the main westerly current, and
thus move relatively slowly (see cutoff low).
Cloud Streets - Rows of cumulus or cumulus-type clouds aligned parallel to the low-level
flow. Cloud streets sometimes can be seen from the ground, but are seen best on satellite
Cloud Tags - Ragged, detached cloud fragments; fractus or scud.
Cold Advection - Transport of cold air into a region by horizontal winds.
Cold-air Funnel - A funnel cloud or (rarely) a small, relatively weak tornado that can
develop from a small shower or thunderstorm when the air aloft is unusually cold (hence
the name). They are much less violent than other types of tornadoes.
Cold Pool - A region of relatively cold air, represented on a weather map analysis as a
relative minimum in temperature surrounded by closed isotherms. Cold pools aloft represent
regions of relatively low stability, while surface-based cold pools are regions of
relatively stable air.
Collar Cloud - A generally circular ring of cloud that may be
observed on rare occasions surrounding the upper part of a wall
This term sometimes is used (incorrectly) as a synonym for wall cloud.
Comma Cloud - A synoptic scale cloud pattern with a characteristic comma-like shape, often
seen on satellite photographs associated with large and intense low-pressure systems.
Comma Echo - A thunderstorm radar echo which has a comma-like shape.
It often appears during latter stages in the life cycle of a bow
Condensation Funnel - A funnel-shaped cloud associated with rotation and consisting of
condensed water droplets (as opposed to smoke, dust, debris, etc.). Compare with debris
Confluence - A pattern of wind flow in which air flows inward toward an axis oriented
parallel to the general direction of flow. It is the opposite of difluence. Confluence is
not the same as convergence. Winds often accelerate as they enter a confluent zone,
resulting in speed divergence which offsets the (apparent) converging effect of the
Congestus (or Cumulus Congestus) - same as towering cumulus.
Convection - Generally, transport of heat and moisture by the movement of a fluid. In
meteorology, the term is used specifically to describe vertical transport of heat and
moisture, especially by updrafts and downdrafts in an unstable atmosphere. The terms
"convection" and "thunderstorms" often are used interchangeably,
although thunderstorms are only one form of convection. Cbs, towering cumulus clouds, and
ACCAS clouds all are visible forms of convection. However, convection is not always made
visible by clouds. Convection which occurs without cloud formation is called dry
convection, while the visible convection processes referred to above are forms of moist
Convective Outlook (sometimes called AC) - A forecast containing the area(s) of expected
thunderstorm occurrence and expected severity over the contiguous United States, issued
several times daily by the SPC. The terms approaching, slight risk, moderate risk, and
high risk are used to describe severe thunderstorm potential. Local versions sometimes are
prepared by local NWS offices.
Convective Temperature - The approximate temperature that the air
near the ground must warm to in order for surface-based convection
to develop, based on analysis of a sounding.
Calculation of the convective temperature involves many assumptions, such that
thunderstorms sometimes develop well before or well after the convective temperature is
reached (or may not develop at all). However, in some cases the convective temperature is
a useful parameter for forecasting the onset of convection.
Convergence - A contraction of a vector field; the opposite of divergence. Convergence in
a horizontal wind field indicates that more air is entering a given area than is leaving
at that level. To compensate for the resulting "excess," vertical motion may
result: upward forcing if convergence is at low levels, or downward forcing (subsidence)
if convergence is at high levels. Upward forcing from low-level convergence increases the
potential for thunderstorm development (when other factors, such as instability, are
favorable). Compare with confluence.
Core Punch - [Slang], a penetration by a vehicle into the heavy precipitation core of a
Core punching is not a recommended procedure for storm spotting.
Cumuliform Anvil - A thunderstorm anvil with visual characteristics resembling
cumulus-type clouds (rather than the more typical fibrous appearance associated with
cirrus). A cumuliform anvil arises from rapid spreading of a thunderstorm updraft, and
thus implies a very strong updraft. See anvil rollover, knuckles, mushroom.
Cumulus - Detached clouds, generally dense and with sharp outlines, showing vertical
development in the form of domes, mounds, or towers. Tops normally are rounded while bases
are more horizontal. See Cb, towering cumulus.
Cumulus Congestus (or simply Congestus) - Same as towering cumulus.
Cutoff Low - A closed low which has become completely displaced (cut off) from basic
westerly current, and moves independently of that current. Cutoff lows may remain nearly
stationary for days, or on occasion may move westward opposite to the prevailing flow
aloft (i.e., retrogression).
"Cutoff low" and "closed low" often are used interchangeably to
describe low pressure centers aloft. However, not all closed lows are completely removed
from the influence of the basic westerlies. Therefore, the recommended usage of the terms
is to reserve the use of "cutoff low" only to those closed lows which clearly
are detached completely from the westerlies.
Cyclic Storm - A thunderstorm that undergoes cycles of intensification and weakening
(pulses) while maintaining its individuality. Cyclic supercells are capable of producing
multiple tornadoes (i.e., a tornado family) and/or several bursts of severe weather.
A storm which undergoes only one cycle (pulse), and then dissipates, is known as a pulse
Cyclogenesis - Development or intensification of a low-pressure center (cyclone).
*Cyclonic Circulation (or Cyclonic Rotation) - Circulation (or rotation) which is in the
same sense as the Earth's rotation, i.e., counterclockwise (in the Northern Hemisphere) as
would be seen from above. Nearly all mesocyclones and strong or violent tornadoes exhibit
cyclonic rotation, but some smaller vortices, such as gustnadoes, occasionally rotate
anticyclonically (clockwise). Compare with anticyclonic rotation.
dBZ - Nondimensional "unit" of radar reflectivity which represents a logarithmic
power ratio (in decibels, or dB) with respect to radar reflectivity factor, Z.
The value of Z is a function of the amount of radar beam energy that is backscattered by a
target and detected as a signal (or echo). Higher values of Z (and dBZ) thus indicate more
energy being backscattered by a target. The amount of backscattered energy generally is
related to precipitation intensity, such that higher values of dBZ that are detected from
precipitation areas generally indicate higher precipitation rates. However, other factors
can affect reflectivity, such as width of the radar beam, precipitation type, drop size,
or the presence of ground clutter or AP. WSR-88D radars can detect reflectivities as low
as -32 dBZ near the radar site, but significant (measurable) precipitation generally is
indicated by reflectivities of around 15 dBZ or more. Values of 50 dBZ or more normally
are associated with heavy thunderstorms, perhaps with hail, but as with most other
quantities, there are no reliable threshold values to confirm the presence of hail or
severe weather in a given situation. See VIP for threshold dBZ values associated with each
*Debris Cloud - A rotating "cloud" of dust or debris, near or on the ground,
often appearing beneath a condensation funnel and surrounding the base of a tornado.
This term is similar to dust whirl, although the latter typically refers to a circulation
which contains dust but not necessarily any debris. A dust plume, on the other hand, does
not rotate. Note that a debris cloud appearing beneath a thunderstorm will confirm the
presence of a tornado, even in the absence of a condensation funnel.
Delta T - A simple representation of the mean lapse rate within a layer of the atmosphere,
obtained by calculating the difference between observed temperatures at the bottom and top
of the layer. Delta Ts often are computed operationally over the layer between pressure
levels of 700 mb and 500 mb, in order to evaluate the amount of instability in mid-levels
of the atmosphere. Generally, values greater than about 18 indicate sufficient instability
for severe thunderstorm development.
Derecho - (Pronounced deh-REY-cho), a widespread and usually fast-moving windstorm
associated with convection. Derechos include any family of downburst clusters produced by
an extratropical MCS, and can produce damaging straight-line winds over areas hundreds of
miles long and more than 100 miles across.
Dew Point (or Dew-point Temperature) - A measure of atmospheric moisture. It is the
temperature to which air must be cooled in order to reach saturation (assuming air
pressure and moisture content are constant).
Differential Motion - Cloud motion that appears to differ relative to other nearby cloud
elements, e.g. clouds moving from left to right relative to other clouds in the foreground
or background. Cloud rotation is one example of differential motion, but not all
differential motion indicates rotation. For example, horizontal wind shear along a gust
front may result in differential cloud motion without the presence of rotation.
Difluence (or Diffluence) - A pattern of wind flow in which air moves outward (in a
"fan-out" pattern) away from a central axis that is oriented parallel to the
general direction of the flow. It is the opposite of confluence.
Difluence in an upper level wind field is considered a favorable condition for severe
thunderstorm development (if other parameters are also favorable). But difluence is not
the same as divergence. In a difluent flow, winds normally decelerate as they move through
the region of difluence, resulting in speed convergence which offsets the apparent
diverging effect of the difluent flow.
Directional Shear - The component of wind shear which is due to a change in wind direction
with height, e.g., southeasterly winds at the surface and southwesterly winds aloft. A
veering wind with height in the lower part of the atmosphere is a type of directional
shear often considered important for tornado development.
Diurnal - Daily; related to actions which are completed in the course of a calendar day,
and which typically recur every calendar day (e.g., diurnal temperature rises during the
day, and diurnal falls at night).
Divergence - The expansion or spreading out of a vector field; usually said of horizontal
winds. It is the opposite of convergence. Divergence at upper levels of the atmosphere
enhances upward motion, and hence the potential for thunderstorm development (if other
factors also are favorable).
Doppler Radar - Radar that can measure radial velocity, the instantaneous component of
motion parallel to the radar beam (i.e., toward or away from the radar antenna).
*Downburst - A strong downdraft resulting in an outward burst of damaging winds on or near
the ground. Downburst winds can produce damage similar to a strong tornado. Although
usually associated with thunderstorms, downbursts can occur with showers too weak to
produce thunder. See dry and wet microburst.
Downdraft - A small-scale column of air that rapidly sinks toward the ground, usually
accompanied by precipitation as in a shower or thunderstorm. A downburst is the result of
a strong downdraft.
Downstream - In the same direction as a stream or other flow, or toward the direction in
which the flow is moving.
Dry Adiabat - A line of constant potential temperature on a
Dry Line - A boundary separating moist and dry air masses, and an important factor in
severe weather frequency in the Great Plains. It typically lies north-south across the
central and southern high Plains states during the spring and early summer, where it
separates moist air from the Gulf of Mexico (to the east) and dry desert air from the
southwestern states (to the west). The dry line typically advances eastward during the
afternoon and retreats westward at night. However, a strong storm system can sweep the dry
line eastward into the Mississippi Valley, or even further east, regardless of the time of
day. A typical dry line passage results in a sharp drop in humidity (hence the name),
clearing skies, and a wind shift from south or southeasterly to west or southwesterly.
(Blowing dust and rising temperatures also may follow, especially if the dry line passes
during the daytime; see dry punch). These changes occur in reverse order when the dry line
retreats westward. Severe and sometimes tornadic thunderstorms often develop along a dry
line or in the moist air just to the east of it, especially when it begins moving
eastward. See LP storm.
Dry-line Bulge - A bulge in the dry line, representing the area where dry air is advancing
most strongly at lower levels (i.e., a surface dry punch). Severe weather potential is
increased near and ahead of a dry line bulge.
Dry-line Storm - Generally, any thunderstorm that develops on or near a dry line. The term
often is used synonymously with LP storm, since the latter almost always occurs near the
Dry Microburst - A microburst with little or no precipitation reaching the ground; most
common in semi-arid regions. They may or may not produce lightning. Dry microbursts may
develop in an otherwise fair-weather pattern; visible signs may include a cumulus cloud or
small Cb with a high base and high-level virga, or perhaps only an orphan anvil from a
dying rain shower. At the ground, the only visible sign might be a dust plume or a ring of
blowing dust beneath a local area of virga. Compare with wet microburst.
Dry Punch - [Slang], a surge of drier air; normally a synoptic-scale or mesoscale process.
A dry punch at the surface results in a dry line bulge. A dry punch aloft above an area of
moist air at low levels often increases the potential for severe weather.
Dry Slot - A zone of dry (and relatively cloud-free) air which wraps east- or
northeastward into the southern and eastern parts of a synoptic scale or mesoscale low
pressure system. A dry slot generally is seen best on satellite photographs.
Dry slot should not be confused with clear slot, which is a storm-scale phenomenon.
Dust Devil - A small atmospheric vortex not associated with a thunderstorm, which is made
visible by a rotating cloud of dust or debris (dust whirl). Dust devils form in response
to surface heating during fair, hot weather; they are most frequent in arid or semi-arid
*Dust Plume - A non-rotating "cloud" of dust raised by straight-line winds.
Often seen in a microburst or behind a gust front.
If rotation is observed, then the term dust whirl or debris cloud should be used.
*Dust Whirl - A rotating column of air rendered visible by dust. Similar to debris cloud;
see also dust devil, gustnado, tornado.
Dynamics - Generally, any forces that produce motion or affect change. In operational
meteorology, dynamics usually refer specifically to those forces that produce vertical
motion in the atmosphere.
ECMWF - European Center for Medium-Range Weather Forecasting. Operational references in
forecast discussions typically refer to the ECMWF's medium-range forecast model. See MRF,
Elevated Convection - Convection occurring within an elevated layer, i.e., a layer in
which the lowest portion is based above the earth's surface. Elevated convection often
occurs when air near the ground is relatively cool and stable, e.g., during periods of
isentropic lift, when an unstable layer of air is present aloft. In cases of elevated
convection, stability indices based on near-surface measurements (such as the lifted
index) typically will underestimate the amount of instability present. Severe weather is
possible from elevated convection, but is less likely than it is with surface-based
Energy Helicity Index (or EHI) - An index that incorporates vertical shear and
instability, designed for the purpose of forecasting supercell thunderstorms. It is
related directly to storm-relative helicity in the lowest 2 km (SRH, in m2/s2) and CAPE
(in j/kg) as follows:
EHI=(CAPE x SRH)/160,000.
Thus, higher values indicate unstable conditions and/or strong vertical shear. Since both
parameters are important for severe weather development, higher values generally indicate
a greater potential for severe weather. Values of 1 or more are said to indicate a
heightened threat of tornadoes; values of 5 or more are rarely observed, and are said to
indicate potential for violent tornadoes. However, there are no magic numbers or critical
threshold values to confirm or predict the occurrence of tornadoes of a particular
Enhanced V - A pattern seen on satellite infrared photographs of thunderstorms, in which a
thunderstorm anvil exhibits a V-shaped region of colder cloud tops extending downwind from
the thunderstorm core. The enhanced V indicates a very strong updraft, and therefore a
higher potential for severe weather.
Enhanced V should not be confused with V notch, which is a radar signature.
Enhanced Wording - An option used by the SPC in tornado and severe thunderstorm watches
when the potential for strong/violent tornadoes, or unusually widespread damaging
straight-line winds, is high. The statement "THIS IS A PARTICULARLY DANGEROUS
SITUATION WITH THE POSSIBILITY OF VERY DAMAGING TORNADOES" appears in tornado watches
with enhanced wording. Severe thunderstorm watches may include the statement "THIS IS
A PARTICULARLY DANGEROUS SITUATION WITH THE POSSIBILITY OF EXTREMELY DAMAGING WINDS,"
usually when a derecho event is occurring or forecast to occur. See PDS watch.
Entrance Region - The region upstream from a wind speed maximum in a jet stream (jet max),
in which air is approaching (entering) the region of maximum winds, and therefore is
accelerating. This acceleration results in a vertical circulation that creates divergence
in the upper-level winds in the right half of the entrance region (as would be viewed
looking along the direction of flow). This divergence results in upward motion of air in
the right rear quadrant (or right entrance region) of the jet max. Severe weather
potential sometimes increases in this area as a result. See also exit region, left exit
Equilibrium Level (or EL) - On a sounding, the level above the level of free convection
(LFC) at which the temperature of a rising air parcel again equals
the temperature of the environment.
The height of the EL is the height at which thunderstorm updrafts no longer accelerate
upward. Thus, to a close approximation, it represents the height of expected (or ongoing)
thunderstorm tops. However, strong updrafts will continue to rise past the EL before
stopping, resulting in storm tops that are higher than the EL. This process sometimes can
be seen visually as an overshooting top or anvil dome.
The EL typically is higher than the tropopause, and is a more accurate reference for storm
Eta Model - One of the operational numerical forecast models run at NCEP. The Eta is run
twice daily, with forecast output out to 48 hours.
Exit Region - The region downstream from a wind speed maximum in a jet stream (jet max),
in which air is moving away from the region of maximum winds, and therefore is
decelerating. This deceleration results in divergence in the upper-level winds in the left
half of the exit region (as would be viewed looking along the direction of flow). This
divergence results in upward motion of air in the left front quadrant (or left exit
region) of the jet max. Severe weather potential sometimes increases in this area as a
result. See also entrance region, right entrance region.
F scale - See Fujita Scale.
Feeder Bands - Lines or bands of low-level clouds that move (feed) into the updraft region
of a thunderstorm, usually from the east through south (i.e., parallel to the inflow).
Same as inflow bands.
This term also is used in tropical meteorology to describe spiral-shaped bands of
convection surrounding, and moving toward, the center of a tropical cyclone.
*Flanking Line - A line of cumulus or towering cumulus clouds connected to and extending
outward from the most active part of a supercell, normally on the
southwest side. The line normally has a stair-step appearance, with
the tallest clouds closest to the main storm, and generally
coincides with the pseudo-cold front.
Forward Flank Downdraft - The main region of downdraft in the forward, or leading, part of
a supercell, where most of the heavy precipitation is. Compare with
rear flank downdraft.
Front - A boundary or transition zone between two air masses of different density, and
thus (usually) of different temperature. A moving front is named according to the
advancing air mass, e.g., cold front if colder air is advancing.
Fractus - Ragged, detached cloud fragments; same as scud.
Fujita Scale (or F Scale) - A scale of wind damage intensity in which wind speeds are
inferred from an analysis of wind damage:
F0 (weak): 40- 72 mph, light damage.
F1 (weak): 73-112 mph, moderate damage.
F2 (strong): 113-157 mph, considerable damage.
F3 (strong): 158-206 mph, severe damage.
F4 (violent): 207-260 mph, devastating damage.
F5 (violent): 261-318 mph, (rare) incredible damage.
All tornadoes, and most other severe local windstorms, are assigned a single number from
this scale according to the most intense damage caused by the storm.
*Funnel Cloud - A condensation funnel extending from the base of a towering cumulus or Cb,
associated with a rotating column of air that is not in contact with the ground (and hence
different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if
either a) it is in contact with the ground or b) a debris cloud or dust whirl is visible
Ground Clutter - A pattern of radar echoes from fixed ground targets (buildings, hills,
etc.) near the radar. Ground clutter may hide or confuse precipitation echoes near the
Gunge - [Slang], anything in the atmosphere that restricts visibility for storm spotting,
such as fog, haze, precipitation (steady rain or drizzle), widespread low clouds
Gust Front - The leading edge of gusty surface winds from thunderstorm downdrafts;
sometimes associated with a shelf cloud or roll cloud. See also downburst, gustnado,
Gustnado (or Gustinado) - [Slang], gust front tornado. A small tornado, usually weak and
short-lived, that occurs along the gust front of a thunderstorm. Often it is visible only
as a debris cloud or dust whirl near the ground. Gustnadoes are not associated with
storm-scale rotation (i.e. mesocyclones); they are more likely to be associated visually
with a shelf cloud than with a wall cloud.
Helicity - A property of a moving fluid which represents the potential for helical flow
(i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional
to the strength of the flow, the amount of vertical wind shear, and the amount of turning
in the flow (i.e. vorticity). Atmospheric helicity is computed from the vertical wind
profile in the lower part of the atmosphere (usually from the surface up to 3 km), and is
measured relative to storm motion. Higher values of helicity (generally, around 150 m2/s2
or more) favor the development of mid-level rotation (i.e. mesocyclones). Extreme values
can exceed 600 m2/s2.
High Risk (of severe thunderstorms) - Severe weather is expected to affect more than 10
percent of the area. A high risk is rare, and implies an unusually dangerous situation and
usually the possibility of a major severe weather outbreak. (See slight risk, moderate
risk, convective outlook.)
Hodograph - A plot representing the vertical distribution of horizontal winds, using polar
coordinates. A hodograph is obtained by plotting the end points of the wind vectors at
various altitudes, and connecting these points in order of increasing height.
Interpretation of a hodograph can help in forecasting the subsequent evolution of
thunderstorms (e.g., squall line vs. supercells, splitting vs. non-splitting storms,
tornadic vs. nontornadic storms, etc.).
Hook (or Hook Echo) - A radar reflectivity pattern characterized by a hook-shaped
extension of a thunderstorm echo, usually in the right-rear part of the storm (relative to
its direction of motion). A hook often is associated with a mesocyclone,
and indicates favorable conditions for tornado development.
HP Storm or HP Supercell - High-Precipitation storm (or High-Precipitation supercell). A
supercell thunderstorm in which heavy precipitation (often including hail) falls on the
trailing side of the mesocyclone. Precipitation often totally envelops the region
of rotation, making visual identification of any embedded tornadoes difficult and very
dangerous. Unlike most classic supercells, the region of rotation in many HP storms
develops in the front-flank region of the storm (i.e., usually in the eastern portion). HP
storms often produce extreme and prolonged downburst events, serious flash flooding, and
very large damaging hail events.
Mobile storm spotters are strongly advised to maintain a safe distance from any storm that
has been identified as an HP storm; close observations (e.g., core punching) can be
extremely dangerous. See bear's cage.
Humidity - Generally, a measure of the water vapor content of the air. Popularly, it is
used synonymously with relative humidity.
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