Lee's Weather

Weather Glossary - T

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Temperature - the degree of hotness or coldness as measured on some definite temperature scale

Temperature Gradient - the gradient of the temperature field; the rate of change of temperature over some distance in a given direction, usually horizontally or vertically

Temperature Inversion - a layer in which air temperature increases with height

Terrestrial Radiation - the total amount of infrared radiation which is emitted from the earth's surface or atmosphere

Thermistor - an electrical resistor making us of a semiconductor whose resistance varies sharply in a known manner with the temperature

Thermodynamic Chart (or Thermodynamic Diagram) - a chart containing isopleths (contours) of pressure, temperature, moisture, and potential temperature, all drawn relative to each other such that basic thermodynamic laws are satisfied (e.g., conservation of energy). 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.

Thermodynamics - the relationships between heat and other properties (such as temperature, pressure, density, etc.)

Thermal Ridge - an axis of relatively high values of temperature

Thermometer - an instrument for measuring temperature consisting typically of a glass bulb attached to a fine tube of glass with a numbered scale and containing a liquid that is sealed in and rises and falls with changes of temperature

Theta-e - see equivalent potential temperature

Theta-e Ridge - an axis of relatively high values of equivalent potential temperature. Severe weather and excessive rainfall often occur near or just upstream from a theta-e ridge.

Thin Line - a line of reflectivity separating air of differing densities. Thin lines typically are located ahead of a thunderstorm, but can be associated with cold fronts and dry lines. The thin line is caused by backscattering of the radar's pulse off of a gradient in the index of refraction of air (i.e, a sharp contrast in air density across a short distance).

3-body hail spike - see hail spike

Thunder - the sound that follows a flash of lightning and is caused by sudden expansion of the air in the path of the electrical discharge

Thunderstorm - a local storm produced by a cumulonimbus cloud, always with lightning and thunder, and usually accompanied by strong gusts of wind, heavy rain, and sometimes hail

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 protruding from a cumulonimbus cloud and in contact with the ground; a condensation funnel does not need to reach to the ground for a tornado to be present

Tornado Warning - issued by the local National Weather Service office when a tornado or funnel cloud has been sighted visually or detected by radar; the location and direction of movement, if know, are given, and residents of the warning area should take immediate safety precautions

Tornado Watch - issued by the Storm Prediction Center in Norman, OK as a precautionary alert when conditions are favorable for the development of tornadoes in the specific area

Total-Totals Index - a measure of stability and used as a 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. In general, values of less than 50 or greater than 55 are considered weak and strong indicators, respectively, of potential severe storm development.

Towering Cumulus - a large cumulus cloud with great vertical development, usually with a cauliflower-like appearance, but lacking the characteristic anvil of a cumulonimbus; same as "towering cu", and abbreviated TCU

Trace (of Precipitation) - an amount of precipitation less than 0.005 inches

Trade Winds - the wind system, occupying most of the tropics, which are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere

Transpiration - the process by which plants transfer water within to water vapor in the atmosphere

Triple Point - the intersection point between two boundaries (dry line, outflow boundary, cold front, etc.) OR 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 favored location for thunderstorm development in the former definition and tornado development (or redevelopment) in the latter definition.

Tropical Cyclone - the general term for a large low pressure system that originates over the tropical oceans; includes tropical depressions, tropical storms, and hurricanes

Tropical Depression - a tropical cyclone with winds equal to or less than 27 knots

Tropical Storm - a tropical cyclone with winds stronger than 27 knots but less than 66 knots

Tropopause - the upper boundary of the troposphere, usually characterized by an abrupt change in how the temperature changes with height; below the tropopause temperature generally decreases with height; above the tropopause temperature generally increases with height

Troposphere - the portion of the atmosphere which extends outward about 10 to 20 km from the earth's surface, and in which generally temperature decreases rapidly with altitude, clouds form, and convection is active

Trough - an elongated area of relatively low atmospheric pressure; the opposite of ridge

True North - the direction from any point on the earth's surface toward the geographic North Pole

Turbulence - irregular atmospheric motion especially when characterized by up and down currents

TVS (Tornadic Vortex Signature) - a distinct feature in the Doppler radar radial velocity field; it indicates intense, concentrated rotation -- more so than that of a mesocyclone. Existence of a TVS strongly increases the probability of tornado occurrence, but does not guarantee it. A TVS is not a visually observable feature.

Typhoon - a hurricane which occurs in the region of the Philippines or the China Sea