slang for 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 unobstructed, this storm often has a higher chance of strengthening to severe levels than the other storms in the line.
see Towering Cumulus
linkage between changes in atmospheric circulation that occurs in widely separated parts of the globe. It is similar to when you touch the surface of a pond--the ripples you cause move across the pond and interact with other waves. So, if you poke one area, another is affected, sometimes at a great distance from the original poke.
a layer in which air temperature increases with height
instability due to a heavy fluid (such as cold, dense air) being over a light fluid (such as warm, moist air). This is also known as potential instability and convective instability. The greater the temperature or density difference between these two fluids, the greater the instability.
an axis of relatively high values of temperature
an electrical resistor that makes use of a semiconductor whose resistance varies sharply in a known manner with the temperature. Using this instrument, we can quickly measure temperature.
as one descends from the surface of the ocean, the temperature remains nearly the same as it was at the surface, but at a certain depth, temperature starts decreasing rapidly with depth. This boundary is the thermocline. This boundary slopes between the western and eastern Pacific differently depending on whether there is an El Niño, a La Niña, or if the conditions are Neutral.
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.
an instrument for measuring temperature that consists typically of a glass bulb attached to a fine tube of glass. It has a numbered scale and contains a liquid that rises and falls with changes of temperature
a layer above the Mesosphere. Temperature increases with height in this layer because oxygen molecules absorb ultraviolet radiation. However, you would not feel hot in this layer (in fact, you would feel cold) because very few particles would hit you.
the difference in height between two pressure levels. For example, the 1000-500 mb thickness is the height difference between the 1000 mb and 500 mb levels. A higher thickness indicates warming (if you heat a gas, it expands), while a lower thickness indicates cooling (cooling a gas contracts it).
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 a sharp contrast in air density across a short distance.
as temperature approaches absolute zero, the entropy of a system approaches a constant. Only with a pure, perfect crystal (one in which every molecule is identical and the alignment is perfectly even in the substance) can entropy be zero. Water vapor (gas) has high entropy. As it cools and becomes a liquid, it loses some entropy (it has become more organized). When the water cools further, it becomes a solid and loses more entropy. With each step, the vibration of molecules becomes less and less.
thick or thickness; see Thickness
see Hail Spike
a precipitation gage where collected water is funneled into a two compartment bucket; 0.01 in, 0.1mm, or some other designed quantity of rain will fill one compartment and overbalance the bucket so that it tips, emptying into a reservoir and moving the second compartment into place beneath the funnel. As the bucket is tipped, it activates an electric circuit. The total precipitation is determined by counting the tips.
cloud top (often used to refer to the height of the cloud top)
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, other than via radar.
a violently rotating column of air hanging 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. If a rotating debris cloud is present, even if there is no condensation funnel, it is a tornado.
a colloquial term used in reference to the area of the United States in which tornadoes are most frequent (usually the central part of the country). Tornado Alley maps often look different because tornado occurrence can be measured many ways--including by all tornadoes, strong and violent tornadoes only, etc. Keep in mind that tornadoes do happen outside of Tornado Alley all the time.
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 known, are given, and residents of the warning area should take immediate safety precautions
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. There is no need to take shelter yet, but residents should be prepared for possible tornadoes in the area on that day.
a measure of stability that is 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, a value of less than 50 indicates a low chance of severe thunderstorm development. A value greater than 55 indicates a high chance of severe storm development.
an amount of precipitation less than 0.005 inches
when one thunderstorm cell moves downstream, but additional cells form on the upwind side, moving directly over the path of the previous cell. Since relatively small areas under these storms receive tremendous amounts of rain, flash flooding may occur.
1. the intersection point between two boundaries (dry line, outflow boundary, cold front, etc.) OR 2. 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. Definition 1 is a favored location for thunderstorm development, while Definition 2 is a favored location for tornado development (or redevelopment).
a large area of air that formed over a warm surface.
one of 9 NCEP Centers. It includes the National Hurricane Center (NHC) and provides forecasts of the movement and strength of tropical weather systems and issues watches and warnings for the U.S. and surrounding areas. This center is located in Miami, Florida.
a low-pressure area that has tropical characteristics (lots of moisture and warm temperatures). Tropical systems include cyclones, hurricanes, typhoons, tropical storms, and tropical depressions. They develop over large bodies of warm water and lose their strength if they move over land.
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 (at least through the Stratosphere).
the portion of the atmosphere that extends outward about 10 to 20 km from the earth’s surface, and in which temperature generally decreases rapidly with altitude, clouds form, and convection is active
an area of intense lift where heavy precipitation may form during winter weather
see Tropical Storm
slang for a narrow, individual cloud tower that develops and falls apart rapidly (it may be tall and thin like a turkey's neck). The sudden development of turkey towers from small cumulus clouds may signify the breaking of a cap.
another name for a Tornado
another name for a hurricane that occurs in the region of the Philippines or the China Sea