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FRONTS, STORMS, AND OTHER WEATHER ANALYSIS
Warm Front
A transition zone between a mass of warm air and the colder air it is replacing.
Wintry Precipitation Types :
A visible aggregate of minute water droplets or ice particles in the atmosphere above the Earth's surface. Clouds form when water vapor deposits on condensation nuclei and grow in an relatively moist environment.
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 due to mixing and a very deep boundary layer on the west side.
The process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc.
In meteorology, the term is used specifically to describe vertical transport of heat and moisture in the atmosphere, especially by updrafts and downdrafts in an unstable atmosphere. The terms "convection" and "thunderstorms" often are used interchangeably.
Supercell
Potentially the most dangerous of the convective storm types. Storms possessing this structure have been observed to generate the vast majority of long-lived strong and violent (F2-F5) tornadoes, as well as downburst wind damage and large hail.
Convection occurring within an elevated layer of unstable air, 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.
Squall Line
A line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms.
Grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud. Striations often reveal the presence of rotation.
Wind Shear (Speed vs Directional)
The rate at which wind velocity changes from point to point in a given direction (as, vertically). The shear can be speed shear (where speed changes between the two points, but not direction), direction shear (where direction changes between the two points, but not speed) or a combination of the two.
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.
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 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg.
Tornado
A small-scale current of rising and violently rotating air. If the air is sufficiently moist, then the moisture condenses into a visible tube, funnel connecting the cloud base to the ground.
A small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cumulonimbus.
A small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cumulonimbus.
Lightning
A visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between the cloud and air, between a cloud and the ground or between the ground and a cloud.
Flash Flood
A rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event.
Tropical Wave
A trough or cyclonic curvature maximum in the trade wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere or may be the reflection of an upper tropospheric cold low or an equatorward extension of a mid-latitude trough.
Hurricane
A tropical cyclone in the Atlantic, Caribbean Sea, Gulf of Mexico, or eastern Pacific, which the maximum 1-minute sustained surface wind is 64 knots (74 mph) or greater.
Eye
The relatively calm center in a hurricane that is more than one half surrounded by wall cloud. The winds are light, the skies are partly cloudy or even clear (the skies are usually free of rain) and radar depicts it as an echo-free area within the eye wall.
A tropical cyclone in which the maximum 1-minute sustained surface wind ranges from 34 to 63 knots (39 to 73 mph) inclusive.
Eye Wall
An organized band of cumuliform clouds that immediately surrounds the center (eye) of a hurricane. The fiercest winds and most intense rainfall typically occur near the eye wall.
Blizzard
Low Pressure System
High (High Pressure)
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone.
A region of high pressure; also known as an anticyclone. Clockwise flow in the northern-hemisphere; counterclockwise in the southern hemisphere. Generally promotes subsiding air and calm weather conditions.
Cold Front
A zone separating two air masses, of which the cooler, denser mass is advancing and replacing the warmer.
Occluded Front
A composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front. There are also new theories on how the occlusion process happens within a mid-latitude cyclone.
Stationary Front
A front between warm and cold air masses that is moving very slowly or not at all.
Dry Line
Frontogenesis
The initial formation of a front or frontal zone via increasing temperature/pressure gradients. Can occur at other levels in the atmosphere besides the surface. Its most important application is the enhancement of vertical motion leading to mesoscale bands of heavier precipitation.
Cloud
Precipitation
Convection
Elevated Convection
Surface-Based Convection
Convection occurring within a surface-based layer, i.e., a layer in which the lowest portion is based at or very near the earth's surface. Compare with elevated convection.
Striations
Updraft
Capping Inversion "The Cap"
Mesocyclone
Flash Flood Guidance
Flood (River)
Downburst/Microburst
Wall Cloud
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 and produce thunderstorms. 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.
A localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.
A convective downdraft with an affected outflow area of less than 2½ miles wide and peak winds lasting less than 5 minutes. Microbursts may induce dangerous horizontal/vertical wind shears, which can adversely affect aircraft performance and cause property damage.
Any high flow, overflow, or inundation by water which causes or threatens damage
Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g., how much rainfall over a given area will be required to produce flash flooding).
Saffir-Simpson Scale
Storm Surge
Tropical Depression
Tropical Storm
A tropical cyclone in which the maximum 1-minute sustained surface wind is 33 knots (38 mph) or less.
The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the hurricane's intensity at the indicated time. The scale provides examples of the type of damage and impacts in the United States associated with winds of the indicated intensity.
An abnormal rise in sea level accompanying a hurricane or other intense storm, whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone.
Sustained wind or frequent gusts to 35 miles an hour or greater; and considerable falling and/or blowing snow. Conditions must last for 3 hours or longer.
Lake-Effect Snow
Snow showers that are created when cold, dry air passes over a large warmer lake, such as one of the Great Lakes, and picks up moisture and heat.
Snowcover
Also known as Snow Pack; the combined layers of snow and ice on the ground at any one time.
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