*Tail Cloud - A horizontal, tail-shaped cloud (not a funnel
cloud) at low levels extending from the precipitation cascade region
of a supercell toward the wall cloud (i.e., it usually is observed
extending from the wall cloud toward the north or northeast). The
base of the tail cloud is about the same as that of the wall cloud.
Cloud motion in the tail cloud is away from the precipitation and
toward the wall cloud, with rapid upward motion often observed near
the junction of the tail and wall clouds. See Fig. 7, supercell.
Compare with beaver tail, which is a form of inflow band that
normally attaches to the storm's main updraft (not to the wall
cloud) and has a base at about the same level as the updraft base
(not the wall cloud).
Tail-end Charlie - [Slang], the thunderstorm at the
southernmost end of a squall line or other line or band of
thunderstorms. Since low-level southerly inflow of warm, moist air
into this storm is relatively unimpeded, such a storm often has a
higher probability of strengthening to severe levels than the other
storms in the line.
Thermodynamic Chart (or Thermodynamic Diagram) - A chart
containing contours of pressure, temperature, moisture, and
potential temperature, all drawn relative to each other such that
basic thermodynamic laws are satisfied. Such a chart typically is
used to plot atmospheric soundings, and to estimate potential
changes in temperature, moisture, etc. if air were displaced
vertically from a given level. A thermodynamic chart thus is a
useful tool in diagnosing atmospheric instability. (See Fig. 6,
Thermodynamics - In general, the relationships between heat
and other properties (such as temperature, pressure, density, etc.)
In forecast discussions, thermodynamics usually refers to the
distribution of temperature and moisture (both vertical and
horizontal) as related to the diagnosis of atmospheric instability.
Theta-e (or Equivalent Potential Temperature) -
a parcel of air would have if a) it was lifted until it became
saturated, b) all water vapor was condensed out, and c) it was
returned adiabatically (i.e., without transfer of heat or mass) to a
pressure of 1000 millibars. Theta-e, which typically is expressed in
degrees Kelvin, is directly related to the amount of heat present in
an air parcel. Thus, it is useful in diagnosing atmospheric
Theta-e Ridge - An axis of relatively high values of theta-e.
Severe weather and excessive rainfall often occur near or just
upstream from a theta-e ridge.
Tilt Sequence - Radar term indicating that the radar antenna
is scanning through a series of antenna elevations in order to
obtain a volume scan.
Tilted Storm or Tilted Updraft - A thunderstorm or cloud tower
which is not purely vertical but instead exhibits a slanted or
tilted character. It is a sign of vertical wind shear, a favorable
condition for severe storm development.
*Tornado - A violently rotating column of air in contact with
the ground and extending from the base of a thunderstorm. A
condensation funnel does not need to reach to the ground for a
tornado to be present; a debris cloud beneath a thunderstorm is all
that is needed to confirm the presence of a tornado, even in the
total absence of a condensation funnel.
Tornado Family - A series of tornadoes produced by a single supercell, resulting in damage path segments along the same general
Total-Totals Index - A stability index and severe weather
forecast tool, equal to the temperature at 850 mb plus the dew point
at 850 mb, minus twice the temperature at 500 mb. The total-totals
index is the arithmetic sum of two other indices: the Vertical
Totals Index (temperature at 850 mb minus temperature at 500 mb) and
the Cross Totals Index (dew point at 850 mb minus temperature at 500
mb). As with all stability indices there are no magic threshold
values, but in general, values of less than 50 or greater than 55
are considered weak and strong indicators, respectively, of
potential severe storm development.
Tower - (Short for towering cumulus), a cloud element showing
appreciable upward vertical development.
Towering Cumulus - (Same as congestus.) A large cumulus cloud
with great vertical development, usually with a cauliflower-like
appearance, but lacking the characteristic anvil of a Cb. (Often
shortened to "towering cu," and abbreviated TCU.)
Transverse Bands - Bands of clouds oriented perpendicular to
the flow in which they are embedded. They often are seen best on
satellite photographs. When observed at high levels (i.e., in cirrus
formations), they may indicate severe or extreme turbulence.
Transverse bands observed at low levels (called transverse rolls or
T rolls) often indicate the presence of a temperature inversion (or
cap) as well as directional shear in the low- to mid-level winds.
These conditions often favour the development of strong to severe
Transverse Rolls - Elongated low-level clouds, arranged in
parallel bands and aligned parallel to the low-level winds but
perpendicular to the mid-level flow. Transverse rolls are one type
of transverse band, and often indicate an environment favorable for
the subsequent development of supercells. Since they are aligned
parallel to the low-level inflow, they may point toward the region
most likely for later storm development.
T Rolls - [Slang], same as transverse rolls.
Triple Point - The intersection point between two boundaries
(dry line, outflow boundary, cold front, etc.), often a focus for
Triple point also may refer to a point on the gust front of a
supercell, where the warm moist inflow, the rain-cooled outflow from
the forward flank downdraft, and the rear flank downdraft all
intersect; this point is a favoured location for tornado development
Tropopause - The upper boundary of the troposphere, usually
characterized by an abrupt change in lapse rate from positive
(decreasing temperature with height) to neutral or negative
(temperature constant or increasing with height). See Fig. 6,
Troposphere - The layer of the atmosphere from the earth's
surface up to the tropopause, characterized by decreasing
temperature with height (except, perhaps, in thin layers - see
inversion, cap), vertical wind motion, appreciable water vapor
content, and sensible weather (clouds, rain, etc.).
Trough - An elongated area of relatively low atmospheric
pressure, usually not associated with a closed circulation, and thus
used to distinguish from a closed low. The opposite of ridge.
Turkey Tower - [Slang], a narrow, individual cloud tower that
develops and falls apart rapidly. The sudden development of turkey
towers from small cumulus clouds may signify the breaking of a cap.
TVS - Tornadic Vortex Signature. Doppler radar signature in
the radial velocity field indicating intense, concentrated rotation
- more so than a mesocyclone. Like the mesocyclone, specific
criteria involving strength, vertical depth, and time continuity
must be met in order for a signature to become a TVS. Existence of a
TVS strongly increases the probability of tornado occurrence, but
does not guarantee it. A TVS is not a visually observable feature.