Weather Glossary: T's

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.

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). See supercell.

It is a theoretical wind that blows parallel to the thickness lines, for the layer considered, analogous to how the geostrophic wind blows parallel to the height contours. The closer the thickness isopleths, the stronger the thermal wind. Cold air is always located to the left of the thermal wind (as you face downstream) and the warm air is located on the right.

Since thickness contours are tighter on the cold side of thermal wind, your lower thickness values will be found on the left side of the thermal wind. The speed and direction of the thermal wind are determined by vector geometry where the geostrophic wind at the upper level is subtracted from the geostrophic wind at the lower level.

It represents the greatest decrease in equivalent potential temperature measured in a layer beginning at or below 700 mb. Consequently, this stability index evaluates the potential for elevated convection, and adds insight where surface-based indices fail.

It also provides useful information for diagnosing the potential for short-fused flooding events, especially when warm, moist, unstable air south of a warm or stationary front is forced isentropically over the frontal boundary by significant low-level winds (greater than 20-30 knots/ 23-35 mph / 37-56 km/h). A TEN equal to or exceeding 5-10°C indicates a potential for elevated convection, especially when isentropic lift is probable.

1. Single Cell Thunderstorms,
2. Multicell Thunderstorms, and
3. Severe Supercell Thunderstorm.

They are the periodic (occurring at regular intervals) variations in the surface water level of the oceans, bays, gulfs, and inlets. Tides are the result of the gravitational attraction of the sun and the moon on the earth.

The attraction of the moon is far greater than the attraction of the sun due to the close proximity of the earth and the moon. The sun is 360 times further from the earth than the moon. Therefore, the moon plays a larger role than the sun in producing tides.

Every 27.3 days, the earth and the moon revolve around a common point. This means that the oceans and other water bodies which are affected by the earth-moon system experience a new tidal cycle every 27.3 days. Because of the physical processes which occur to produce the tidal system, there are two high tides and two low tides each day.

Because of the angle of the moon with respect to the earth, the two high tides each day do not have to be of equal height. The same holds true for the two low tides each day.

Tides also differ in height on a daily basis. The daily differences between tidal heights is due to the changing distance between the earth and the moon. Scientists use measurements of the height of the water level to examine tides and the various phenomena which influence tides, such as hurricanes and winter storms.

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.

It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise. Tornadoes are classified by the amount of damage that they cause. See Fujita Scale.

This is issued when a tornado is indicated by the WSR-88D radar or sighted by spotters; therefore, people in the affected area should seek safe shelter immediately. They can be issued without a Tornado Watch being already in effect. They are usually issued for a duration of around 30 minutes.

A Tornado Warning is issued by your local National Weather Service office. It will include where the tornado was located and what towns will be in its path. If the tornado will affect the nearshore or coastal waters, it will be issued as the combined product--Tornado Warning and Special Marine Warning. If the thunderstorm which is causing the tornado is also producing torrential rains, this warning may also be combined with a Flash Flood Warning.

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

This is issued by the National Weather Service when conditions are favorable for the development of tornadoes in and close to the watch area. The watch is in a form of a rectangle whose size and orientation varies depending on the weather situation. They are usually issued for a duration of four to eight hours.

They normally are issued well in advance of the actual occurrence of severe weather. During the watch, people should review tornado safety rules and be prepared to move a place of safety if threatening weather approaches.

• Vertical Totals (VT) = 850 mb temperature - 500 mb temperature
• Cross Totals (CT) = 850 mb dew point - 500 mb temperature

1. A rainfall amount less than 0.01" (.25 mm).
2. A hydrograph or similar plot for an extended-range time horizon showing one of many scenarios generated through an ensemble forecast process.

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 favor the development of strong to severe thunderstorms.

• Scheduled Public Tropical Cyclone Advisory (TCP) - This is one of the most prominent products issued by the hurricane centers. It summarizes all watches or warnings in effect. It includes the location of the storm center in latitude and longitude and in distance from a well-known point. The current movement is given to 16 points of the compass.

  Also, included in this advisory are the maximum sustained wind, pressure, storm tide or storm surge and the radius of both hurricane force and tropical storm force winds (just tropical storm force winds for a tropical storm) and an intensity forecast. If it is going to affect land, inland effects will also be highlighted in this advisory.

  They are issued for all tropical storms and hurricanes in the Atlantic (which includes the Caribbean Sea and the Gulf of Mexico) and central Pacific. In the eastern Pacific, they are issued for all tropical cyclones that are expected to affect land within 48 hours.

  They will cease to be issued when the tropical cyclone becomes extratropical (the storm no longer has tropical characteristics), drops below depression stage, or move inland over large land areas, such as the United States, Mexico, Canada, or Central America.

• Intermediate Public Tropical Cyclone Advisory (TCP) - Issued to ensure a more continuous flow of information to the public whenever a tropical cyclone affects a coast or is forecast to affect a coast. Intermediate advisories will not be used to issue tropical cyclone watches or warnings, but it may be used to clear all or portion of a watch or warning area. The content will be similar to that of the scheduled advisory.
• Special Public Tropical Cyclone Advisory - These will be issued whenever one or more of the following criteria are met:
  1. When conditions require a hurricane/typhoon or tropical storm watch or warning to be issued and/or
  2. A significant change has occurred, requiring the issuance of a revised forecast package.

  The content of special advisories should generally be similar to that of the scheduled advisory. The meteorological condition that requires the issuance of the special advisory is normally highlighted. However, since special advisories are designed to update earlier scheduled advisories, their format and content will be less rigid.

• Scheduled Tropical Cyclone Forecasts/Advisory (TCM) - This is one of the most prominent products issued by the hurricane centers. They are prepared for all tropical cyclones within a Tropical Cyclone Center's area of responsibility. They provide invaluable wind field information to emergency managers, local decision makers, and other users who must prepare and take response actions for inland wind effects of tropical cyclones.

  This product along with the public advisories should be used for decision making purposes. They will be issued at the same time as the Scheduled Public Tropical Cyclone Advisory. They will cease to be issued when the tropical cyclone becomes either extratropical (the storm no longer has tropical characteristics) or drop below depression stage.

• Special Tropical Cyclone Forecast/Advisory (TCM) - This product is issued as needed for conditions that either change abruptly or significantly prior to the next regularly scheduled Tropical Cyclone Forecast/Advisory. They will contain generally the same information as the Tropical Cyclone Forecast/Advisory; however, their format is less stringent.

• Subtropical Cyclone Public Advisory (SPA) - These advisories are issued when a subtropical storm is affecting or is forecasted to affect the U.S., our territories, or our installations. Each subtropical storm is assigned a storm number to keep track of the sequence of occurrences such storms in that area. The contents of the advisory are the same as advisories on depressions; however, subtropical storms are referred to as plain "storms".

  Thus, they are entitled as storm advisories. They are issued at the same scheduled times as hurricane and tropical storm advisories. They are updated as needed for significant changes such as a change in course, a threat of tornadoes being added, or a major change in intensity. For each storm, the advisories are numbered consecutively for the life of the storm.

• Intermediate Subtropical Cyclone Public Advisory (SPA) - These advisories function in the same manner as public intermediate advisories. Whenever a subtropical cyclone affects or is forecasted to affect a coast, they will be issued on a 2 to 3 hourly interval between scheduled advisories. For clarity, whenever the National Hurricane Center is issuing intermediates, a statement will be included at the end of the scheduled public subtropical advisory telling the user that an intermediate advisory will be issued.
• Special Subtropical Cyclone Public Advisory (SPA) - These advisories are issued to update the previously scheduled advisory whenever a significant change in the cyclone has occurred. The change or conditions that require the issuance of the special advisory normally are highlighted.
• Scheduled Subtropical Forecast/Advisory (SMA) - These advisories are issued when a subtropical storm is affecting or is forecasted to affect the U.S., our territories, or our installations. Each subtropical storm is assigned a storm number to keep track of the sequence of occurrences such storms in that area. The contents of the advisory are the same as advisories on depressions; however, subtropical storms are referred to as plain "storms". Thus, they are entitled as storm advisories. They are issued at the same scheduled times as hurricane and tropical storm advisories.
• Special Subtropical Cyclone Forecast/Advisory (SMA) - These advisories will be issued to update any abrupt or significant change that may have occurred with the subtropical cyclone. The format is the same as the scheduled advisory that is being replaced.

The National Hurricane Center issues a position estimate between scheduled advisories whenever the storm center is within 200 nautical miles of U.S. land-based weather radar and if sufficient and regular radar reports are available to the hurricane center.

As far as is possible, the position estimate is issued hourly near the beginning of the hour. The location of the eye or storm center is given in map coordinates and distance and direction from a well-known point.

A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics.

It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a report on every tropical cyclone in its area of responsibility.

• Civil Twilight - The period of time before sunrise and after sunset when the sun is not more than 6° below the horizon.
• Nautical Twilight - The period of time before sunrise and after sunset when the sun is not more than 12° below the horizon.
• Astronomical Twilight - The period of time before sunrise and sunset when the sun is not more than 18° below the horizon.