Monday, June 24, 2013

Forecasting Terminology and Vocabulary

 Using concise terms for weather events helps meteorologists prepare weather forecasts for viewers. But sometimes the  terminology can get confusing. So I thought a post on meteorological  terms and vocabulary, might help clear things up a bit. This post will cover  the most common terms I use or what might be heard during weather forecasts by other weather outlets.
Nothing confuses people faster than words used for predicting  precipitation.
The difference between showers and rain.
The main difference between rain and showers is that rain is more widespread than showers. Rain at times or occasional rain will affect more of a larger area than frequent showers or scattered showers. Showers do not usually affect all areas with precipitation at the same time like rain. Showers have a shorter duration than rain. Showers begin and end more suddenly than rain. They can be short-lived and separated by blue sky or sun. Showers can be more intense, still covering a smaller area, with hail and heavy rain. Rain tends to be more uniformly steady and moderate or light in intensity.

The term "isolated" refers to showers that are few and far between, and the National Weather Service (NWS) defines "isolated" as displaying between 10% to 20% coverage.  In other words, when the forecast calls for "isolated" showers, only 10% to 20% of the forecast area will receive measurable rainfall within the forecast period -- most neighborhoods stay dry.

"Scattered" refers to the range of 30% to 50% coverage.  So, even with "scattered" showers, half or less of the neighborhoods are expected to "get wet."  For 60% and above, the terms most frequently used are "likely" and "numerous."  At 90% to 100% coverage, we often simply say something like "expect showers."
The National Weather Service expresses the probability of measurable precipitation (0.01 inch) for a given location using percentages and terms such as isolated and scattered. Isolated means a chance of precipitation of less than 30% and scattered is used for a 30% to 50% chance. Likely describes a probability of 60 percent or greater.

10% probability: Slight chance, isolated or none.
20% probability: Slight chance, isolated

30-50% probability: Chance, scattered

60-70% probability: Likely, numerous

Duration, Distribution and Intensity of precipitation and clouds.

Duration of Precipitation

Brief - short, sudden showers or periods of rain

Intermittent - on and off intervals, not continuous

Occasional - irregular, infrequent intervals of precipitation

Frequent - persistent short intervals, happening regularly and often

Periods of precipitation - rain or snow falling most of the time with breaks

Distribution of Precipitation, as in showers

 Isolated - showers separated during a given period of time

 Few - indicated in time, not over an area

 Local - restricted to a smaller area

 Patchy - irregularly occurring in an area

 Scattered - not widespread but of greater occurrence than isolated showers

Precipitation Intensity

 Light - each drop or small flake of precipitation can be easily seen, puddles form slowly, some water flow in gutters

 Moderate - water puddles quickly, roads and other surfaces collect water, rain streams down windows

 Heavy - numerous flakes or sheets of rain, large puddles form, flooding can occur, visibility reduced

Snow intensity and visibility

         Light snow          -   Greater than 1/2 mile visibility
         Moderate snow  -   1/4 to 1/2 mile
         Heavy snow       -   Less than 1/4 mile

 Cloud Cover
 Clear or sunny - free of clouds or less than one tenth cloudy

 Partly cloudy or partly sunny - three tenths to six tenths of the sky is clouded

 Mostly cloudy - the sky is predominantly clouded or seven tenths to eight tenths of the sky has clouds

 Cloudy or overcast - the sky is covered with clouds from nine tenths to a hundred percent cloud covered.

Partly Cloudy vs. Partly Sunny

 Yet another confusing set of weather terms are partly sunny and partly cloudy. According to the National Oceanic and Atmospheric Administration there is no official difference between the two terms. It is important for meteorologists forecasting the weather to emphasize one or the other, to help clarify the meaning of the term used.

Ok let's get down to terminology.


 Air Pressure - The weight of air pressing down on earth. Air pressure can change from place to place, and this causes air to move, flowing from areas of high pressure toward areas of low pressure. It’s the same as barometric pressure.

Air Mass Thunderstorm - a normal single cell thunderstorm (also called a pulse thunderstorm)

Alberta Clipper - A fast-moving low pressure system that occurs during the winter and sweeps southeast from Alberta, Canada, across the northern Great Plains and Midwest of the United States. These storms usually bring a few inches of snow.

 Almanac - A calendar that uses astronomical information and weather data. Almanacs list tide data, give the positions of the stars and forecast weather each day.

Alto - A prefix to cloud-type names for clouds generally found between 3000 and 7000 meters. Alto comes from the Latin word meaning "middle".

 Anemometer - A weather instrument that measures the wind speed.

 Anticyclone - A high-pressure system that moves in a clockwise motion. These bring you sunny skies.

Arctic Air - An air mass that originates over Canada and brings us cold temperatures.

Arctic Oscillation Index (AO)-  this deals with the atmospheric circulation over the Arctic . The AO consists of positive and negative phases.  During the positive phase we see below average geopotential heights.  The opposite is true during the negative phase.   In the negative phase The polar low pressure system  (Polar Vortex) is weaker. Since the winds circulation at the Pole is weaker, the arctic air and storm track can move farther south. During the winter this means cold air and stormy pattern for the Great Lakes and Northeast.  The AO often shares the same phase as the North Atlantic Oscillation.

Areal- refers to an area or region.

Atlantic Multidecadal Oscillation (AMO)-  It deals with sea surface temperature (SST) in the North Atlantic. The AMO is characterized by warm and cool phases. These phases typically last 20-40 years. It affects the track of Atlantic storms. We see more Atlantic hurricane activity during the warm phase than we do during the cool phase.

Atmosphere - A layer of gases surrounding a planet. The Earth’s atmosphere is divided into five layers: exosphere, thermosphere, mesosphere, stratosphere, and troposphere.

Aurora Borealis - It’s often called the "northern lights". It occurs 50 to 100 miles above the earth, when energetic particles from a solar storm cause the gases in the upper atmosphere to glow. Auroras can last between a few minutes to several hours. It’s common across Alaska and northern Canada.


Backing Wind - A wind that changes its direction in a counter clockwise motion. For example, a northwest wind changing to a west wind.

Backdoor Cold Front - In the northern hemisphere, weather normally moves from west to east. In the Northeast, most of the time, cold fronts arrive from the northwest or west. But every once in a while an area of high pressure will develop over New England or just off the Northeast coast, since winds move clockwise around the center of high pressure, this air will pass over the relatively cold water of the North Atlantic. As the cooler air moves inland it creates a cold front, sometimes the temperature drop is quite impressive. Because the front is moving northeast to southwest, instead of the normal way, it's called a backdoor cold front.

 Base Radial Velocity - This is the velocity of the precipitation either toward or away from the radar (in a radial direction). No information about the strength of the precipitation is given. This product is available for just two radar "tilt" angles, 0.5° and 1.45°. Positive values (warm colors) denote out-bound velocities that are directed away from the radar. Negative values (cool colors) are in-bound velocities that are directed towards the radar. On most radar packages red means moving away from the radar, Green means moving toward the radar. Precipitation moving perpendicular to the radar beam (in a circle around the radar) will have a radial velocity of zero, and will be colored grey. The velocity is given in knots (10 knots = 11.5 mph).

Barometer - An instrument that measures air pressure.

Barometric Pressure - It’s the same as air pressure. The pressure exerted by the atmosphere at a given point.
Beaufort Wind Scale - A system of estimating and reporting wind speeds. It is based on the

Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. The scale was devised by Sir Francis Beaufort (1777-1857), hydrographer to the British Royal Navy.

Bermuda High - It’s a weather system that often dominates the eastern United States during the summer. A semi-permanent subtropical high-pressure system over the North Atlantic Ocean brings in warm and humid air for many days or weeks at a time. It gets its name because it is sometimes centered near Bermuda. It contributes to U.S. heatwaves when it extends west into the Gulf of Mexico and across the Deep South.
Blizzard - An intense winter storm with winds of 35 m.p.h. or higher with falling and/or blowing snow to reduce visibility below 1/4 mile for at least three hours.
Blizzard Watch - Alerts the public to the potential for blizzard conditions. Watches are usually issued 12 to 48 hours before the beginning of blizzard conditions.

Blizzard Warning - Issued for sustained or gusty winds of 35 mph or more and falling or blowing snow creating visibilities below ¼ mile. These conditions usually persist for at least three hours.

Blowing Snow Advisory - When wind driven snow reduces the surface visibility causing dangerous driving conditions. Blowing snow can be falling or snow that has already accumulated on the ground but is picked up and blown by strong winds.

Breeze - A light wind from 4 to 27 knots (5 to 31 miles per hour.)

C to A - Cloud to air lightning

C to C - Cloud to cloud lightning

C to G - Cloud to ground lightning

Ceiling - The height of the lowest layer of broken or overcast cloud layer.

CAPE - stands for convective available energy. It's a measure of how much energy is available for thunderstorm development. The higher the CAPE the stronger the potential updraft needed to generate thunderstorm, which leads to greater potential for stronger storms.

Cirro - A prefix to cloud-type names for clouds that are at high altitudes and composed of ice crystals.

Cirrus Clouds - Thin, wispy clouds that form high in the atmosphere as their water vapor freezes into ice crystals. Cirrus clouds are a principle cloud type.
Clear Sky - When the sky has no clouds.

Climate - It describes the average weather conditions in a certain place or during a certain season. Weather may change from day to day, but climate changes only over hundreds or thousands of years. Many animals and plants need one kind of climate to survive. Dolphins and palm trees can live only in a warm climate, while polar bears and spruce trees need a cold climate.

Clouds - A visible collection of tiny water droplets or, at colder temperatures, ice crystals floating in the air above the surface. Clouds come in many different sizes and shapes. Clouds can form at ground level, which is fog, at great heights in the atmosphere, and everywhere in between. Clouds offer important clues to understanding and forecasting the weather.

Coastal Flooding - It’s when winds and/or tides cause a rise in the sea level that floods coastal areas.

Coastal Flood Warning - Land areas along the coast are expected to become, or have become, inundated by sea water above the typical tide action.

Coastal Flood Watch - The possibility exists for the inundation of land areas along the coast within the next 12 to 36 hours.

Cold Front - A boundary between two air masses, one cold and the other warm, moving so that the colder air replaces the warmer air.

Condensation - The change of water vapor to liquid water, as when fog or dew forms.

Convection - Motions in a fluid that transport and mix the properties of the fluid. These properties could be heat and/or moisture. When used to imply only upward vertical motion, it is then the opposite of subsidence.

Coriolis Force - A force that deflects moving objects to one side because of the Earth’s rotation. The object is still going straight but the Earth moves underneath it, making it look like it is moving to one side. In the Northern Hemisphere, the Coriolis Force deflects objects to the right.

Composite Reflectivity - images utilize all elevation scans during each volume scan to create the image. It is composed of the greatest echo intensity (reflectivity) from any elevation angle seen from the radar. It is used to reveal the highest reflectivity in all echoes. This product is available for four radar "tilt" angles, 0.5°, 1.45°, 2.40°, and 3.35°.

Cumulonimbus - A dense and vertically developed cloud that produces thunderstorms. The cloud can bring heavy showers, hail, lightning, high winds and sometimes tornadoes.

Cumulus Clouds - Fluffy, mid-level clouds that develop in towering shapes and signal fair weather. Cumulus clouds are a principle cloud type.

Cyclone - A low pressure system. It is a term variously applied to tornadoes, waterspouts, dust storms, hurricanes and even to any strong wind.

Dense Fog - Its fog that reduces horizontal visibility to 1/4 mile or less. Dense fog usually creates traveling problems and delays.

Dense Fog Advisory - It’s issued when dense fog covers a widespread area and reduces visibility to ¼ of a mile or less.

Dew - Water that forms on objects close to the ground when its temperature falls below the dew point of the surface air.

Dew Point - The temperature at which water starts to condense out of a particular air mass. The dew point temperature changes only when the moisture content of the air changes. The higher the dew point, the greater the moisture content is in the air.

Disturbance - A low pressure system, a tropical area of storminess, or any area in which the weather is in a state of cloudiness, precipitation or wind.

Downdraft -  in severe thunderstorms can create gusty winds with speeds that have been recorded as high as 160 mph.

Downburst - A strong downward rush of air from the base of a thunderstorm, which produces a blast of damaging, winds on or close to the surface.
Drifting Snow - An uneven amount of snowfall or existing snow on the ground caused by strong winds. Drifting snow can be very dangerous for drivers.

Drizzle - Light rain consisting of water droplets that are very small.

Drought - A period when a region has a lack of rainfall. Droughts can affect a fairly small area for a season or an entire continent for years. Too little rainfall can cause shortages in the water supply, destroy crops, and cause widespread hunger. Droughts also dry up soil, which then gets picked up by the wind and causes dust storms.

Dry Line - A boundary that separates warm, dry air from warm, moist air. The differences in the two air masses may be significant. The dry line is usually a boundary where thunderstorms form.

Dust Devil - Small whirlwinds of dust that form in dry areas like deserts. They may look like tornadoes, but dust devils are not formed by thunderstorms and do not drop from the sky. Dust devils are caused by swirling winds that rise with the warm air found over the ground.

The EF Scale - The Enhanced F-scale still is a set of wind estimates (not measurements) based on damage. It uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators. It was implemented in place of the Fujita scale introduced in 1971 by  Dr. Fajita , it began operational use in the United States on February 1, 2007, followed by Canada on April 1, 2013.

EF0 (65-85 mph)
Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over.

EF1 (86-110 mph)
Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.

EF2 (111-135 mph)
Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.

EF3 (136-165 mph)
Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance.

EF4 (166-200 mph)
Devastating damage. Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated.

EF5 (200 mph or greater)
Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (109 yd); high-rise buildings have significant structural deformation; incredible phenomena will occur.

El Niño - The unusual warming of the surface waters of the eastern tropical Pacific Ocean. It causes changes in wind patterns that have major effects on weather all across the globe.
Environment - The external conditions and surroundings, especially those that affect the quality of life of plants, animals and human beings.

Eastern Pacific Oscillation (EPO- The EPO is a dipole pattern similar to the NAO in the Atlantic. But located in the Eastern Pacific. It has two phases negative and positive. When in the Positive phase there are lower heights (low pressure) in the Gulf of Alaska. In the US, this promotes a western trough and a eastern ridge.  During the negative phase it is the exact opposite.  During winter a negative EPO pattern Alaska gets warm, and it opens the arctic door allowing cold to invade the lower 48.  

Equator - The imaginary great circle of 0 degrees latitude on the Earth's surface, separating the Northern Hemisphere from the Southern Hemisphere.

Erosion - The wearing away of the Earth’s surface by the action of the sea, running water, moving ice, precipitation or wind.

Evaporation - The process of changing a liquid (like water) to a vapor. It’s the opposite of condensation.

Excessive Heat Warning - It’s issued within 12 hours of the onset of the heat conditions listed in the excessive heat watch.

Excessive Heat Watch - It’s issued when the following conditions occur within 12-36 hours: a heat index of at least 105 degrees for more than 3 hours per day for 2 consecutive days or a heat index more than 115 degrees for any period of time.

Flash Flood - Sudden flooding that occurs when floodwaters rise swiftly with no warning within several hours of an intense rain. They often occur after intense rainfall from slow moving thunderstorms. In narrow canyons and valleys, floodwaters flow faster than on flatter ground and can be quite destructive.

Flash Flood Warning - It’s issued to alert the public, emergency management, and other cooperating agencies that flash flooding is in progress or is likely to happen.

Flood - It results from days of heavy rain and/or melting snows, when rivers rise and go over their banks.

Flood Plain - The lowland that borders a river, usually dry but subject to flooding when the river is high.

Flood Stage - The level at which a stream, river or other body of water begins to or will begin to leave its banks.

Fog - A cloud on the ground that reduces visibility.

Freeze - It occurs when the temperature falls below 32 degrees over a large area for an extended period of time.

Freeze Warning - It’s issued during the growing season when the temperature falls below 32 degrees over a large area for an extended period of time. A freeze can destroy crops.

Freezing Rain - Rain that falls in liquid form but freezes upon impact to form a coating of glaze/ice on the ground and on exposed objects.

Front - A boundary between two different air masses, resulting in stormy weather. A front usually is a line of separation between warm and cold air masses.

Frost - White ice crystals that form on a surface, like the ground or leaves of a plant. Frost is created when the air temperature drops below freezing and the water vapor in the air freezes into ice crystals.

Frost Advisory - It’s issued during the growing season when a widespread frost is expected over an extensive area. Temperatures are usually in the mid 30’s.

Frostbite - It happens when you have excessive exposure to extremely cold weather. It usually affects the toes, fingers, ears, and tip of the nose. Frostbite is rendered more dangerous because there is no sensation of pain, and the victim may not even know that they have been frostbitten.
Fujita Scale - The original scale that measures the strength of tornadoes based primarily on the damage tornadoes inflict on human-built structures and vegetation.

Dr. Tetsuya Theodore Fujita  first introduced The Fujita Scale in the SMRP Research Paper, Number 91, published in February 1971  After. the Super Outbreak of April 3-4, 1974. The F-Scale became the mainstay to define every tornado that has occurred in the United States.

F0: winds 40-72 m.p.h. - (Light damage) Branches broken off trees

F1: winds 73-112 m.p.h. - (Moderate damage) Trees snapped and mobile home pushed off foundations

F2: winds 113-157 m.p.h. - (Considerable damage) Mobile homes demolished and trees uprooted

F3: winds 158-206 m.p.h. - (Severe damage) Trains overturned and cars lifted off the ground

F4: winds 207-260 m.p.h. - (Devastating damage) Houses leveled and cars thrown some distance

F5: winds 261-318 m.p.h. - (Incredible damage) Houses lifted and thrown some distance

Funnel Cloud - A tornado that doesn’t reach the ground. It has a rotating cone-shaped column of air extending downward from the base of a cumulonimbus or thunderstorm cloud, but whose circulation does not make contact with the ground.


Gale - A gale is a very strong wind, The NWS defines a gale as 34–47 knots (39–54 mph) of sustained surface winds.
Glaze - A coating of ice, usually clear and smooth, formed on exposed objects by the freezing of rain, drizzle, or fog.
Global Warming - The theory that increased concentrations of greenhouse gases are causing the Earth’s surface temperature to warm.

You can find out more about this subject here.

Greenhouse Effect - The heating effect of the Earth's atmosphere. The atmosphere acts like a greenhouse because sunlight freely passes through it and warms the surface, but the Earth's re-radiated heat is slowed in its escape from the planet back into space.

Ground Clutter - A pattern of radar echoes from stationary objects like buildings near the radar site. ground clutter can hide or confuse precipitation echoes near the radar antenna.

Ground Fog - A shallow layer of fog on the ground that reduces visibility more in the horizontal than in the vertical.

Graupel - a snowflake t collides with the supercooled water droplets in the cloud.  Those droplets in turn stick to the snowflake branches, ice crystals form instantly on the outside of the snow and accumulate until the original snowflake is no longer visible or distinguishable, it's more of a lump of snow. it is also called ice pellets, soft hail or rimmed snow.

GOM - Gulf Of Mexico.

Gulf Stream - A warm swift current in the Atlantic Ocean that flows from the Gulf of Mexico along the eastern coast of the United States and then northeast toward Europe.

Gustnado - It’s just a gust front tornado. It’s a small and weak tornado that occurs along the gust front of a thunderstorm and doesn’t stay on the ground for long periods of time. Sometimes called a landspout.

Hail - A mixture of liquid and frozen precipitation. Hailstones are composed of layers of ice and can become quite large when strong gusts of upward-moving air keep them inside the cloud. As they move around inside the cloud they collide with raindrops, adding layers and growing before they fall to earth.

Hard Freeze - A freeze when the air temperature is 26 degrees or colder for at least four consecutive hours. It usually means that seasonal vegetation will be destroyed.

Haze - Tiny particles of dust, smoke, salt or pollution droplets that are scattered through the air. The particles are too small to be seen or felt individually, but they diminish visibility.

Heat Advisory - It’s issued within 12 hours of the onset of the following conditions: a heat index of at least 105 degrees but less than 115 degrees for less than 3 hours per day or if nighttime lows remain above 80 degrees for 2 consecutive days.

Heat Burst -  is a downdraft of hot and dry air that typically occurs in the evening or overnight hours. the phenomenon causes a sudden, dramatic rise in temperature, along with strong straight line winds. A heatburst is much rarer than a severe thunderstorm.

Heat Index - It’s the ‘feel like’ temperature on a hot day. The heat index is a number that expresses the warming effect of humidity at different temperatures. Only air temperature and relative humidity are used in the calculation of heat index.

Heat Lightning - There is no such thing as heat lightning. Heat lightning is just ordinary lightning, except that it is too far away for its thunder to be heard or the cloud producing it to be seen.

Heavy Snow Warning - It’s issued when a snowfall totaling 6 inches or more in 12 hours or less is expected. Also, it’s issued when there is 8 inches or more of snow in 24 hours or less.

High Pressure System - A whirling mass of cool, dry air that generally brings fair weather and light winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere. These bring sunny skies.

High Wind Warning -   It's Issued for when sustained winds will be 40 mph or greater for at least one hour, or any gust of wind expected to be 58 mph or greater.

High Wind Watch - It’s issued when conditions are favorable of the development of high winds.
Humidity - The amount of water vapor in the air.
Hurricane - They are intense tropical cyclones with winds up to 170 miles per hour. Once a tropical cyclones winds reach 64.31 knots  (74 mph) it becomes a hurricane.  Hurricane Camille, had estimated max winds of around 174 knots (slightly more than 200 mph); however, the exact wind speeds are unknown due to the fact that she destroyed all of the wind measuring devices in the landfall zone. Usually around 300 miles across, sometimes larger than 1000 miles across . Hurricanes are known by different names around the world. In Japan they are Typhoons, while Australians call them Willy-Willys.

Hurricane Season - In the Atlantic basin, it's a six-month period from June 1 to Nov. 30, when conditions are favorable for hurricane development.

Hygrometer - An instrument that measures the water vapor content of air or the humidity.


Ice - A water substance in the solid phase.
Ice Storms - They occur when temperatures below a raining cloud are very cold, causing the raindrops to become supercooled (less than 32 degrees Fahrenheit). Freezing rain covers streets, houses, and trees with heavy layers of ice, causing concern for dangerous driving, and damage from the weight of the ice.

 Ice Storm Warning - It’s issued when damaging accumulations of ice are expected during a freezing rain event.

Indian Summer - A warm, tranquil spell of weather in the autumn, especially after a period of cold weather. The term is used most often in the Midwest and New England.

Inversion - A layer in the atmosphere where the temperature increases with height.

Isobar - A line connecting equal points of pressure.

Jet Stream - A strong high level wind found in the atmosphere that can reach speeds in excess of 200 mph, usually occurring 6 to 9 miles above the ground. These winds often steer the movement of surface air masses and weather systems.


Killing Frost - The definition of a killing frost is not precise because different plants can withstand temperatures below 32 degrees for varying amounts of time. But generally it's the occurrence of temperatures cold enough to kill all but the hardiest vegetation, especially the last such occurrence in spring and the first in fall, events that limit the agricultural growing season.

Knot- 1 knot (kt) = 1.15077945 miles per hour (mph).


La Niña - A widespread cooling of the surface waters of the eastern tropical Pacific Ocean. It’s the opposite of El Niño.

Lake Breeze - Lake breezes develop when the land becomes warmer than the water.  The warm air over land rises, and gets replaced by the relatively cool air which resides immediately above the lake surface.  You can tell when a lake breeze forms when the wind abruptly becomes "onshore" (blowing from the water toward the shore).  Lake breezes generally form several hours after sunrise, and have speeds of around 10 mph.  Lake breezes generally dissipate in the early evening as the sun begins to set.  The spring and summer are the most common times of year for lake breezes.

Lake breezes can impact the weather in many ways.  In addition to shifting the wind and cooling the temperature, under certain conditions lake breeze boundaries can help to initiate thunderstorms.  Lake breezes are also responsible to keeping lake shores less cloudy, due to the fact that the cooler air found in a lake breeze tends to rise into cloud cover less readily

Lake Effect Snow - Localized snow that forms on the downwind side of large lakes. It’s common in the late fall and winter in the Great Lakes region when cold, dry air picks up moisture from the unfrozen lake surfaces.

Lake Effect Snow Advisory - Issued when 4-5 inches of widespread or localized lake effect snow is expected to fall (for the Northeast normally over the snow belts of Lakes Ontario and Erie) in 12 hours or less.

Lake Effect Snow Warning - Issued for the snow-belts of  Lakes Ontario and Erie when lake effect snow is expected to accumulate to 6 inches or more in 12 hours or less, or 8 inches of snow in 24 hours or less.

Latitude - The position of the Earth’s surface north or south of the equator.

Leeward Side - The side of an object that is facing away from the direction that the wind is blowing.

Lightning - An enormous and very hot spark of electricity produced by thunderstorms. The lightning bolt itself can heat the air through which it travels to 54,000° F.

Longitude - The position of the Earth’s surface east or west of the Greenwich meridian.

Low Pressure System - A whirling mass of warm, moist air that generally brings stormy weather with strong winds. When viewed from above, winds spiral into a low-pressure center in a counterclockwise rotation in the Northern Hemisphere.


Macroburst - A large downdraft of air with an outflow diameter of 2.5 miles or greater and damaging winds lasting from 5 to 20 minutes. This may reach tornado intensity.

Microburst - A small downdraft of air with an outflow diameter of less than 2.5 miles with the peak winds lasting from 2 to 5 minutes. This can effect a planes performance.

Meridional Flow - It’s when the winds in the upper levels of the atmosphere blow from a North to South component which usually creates a buckling effect in the jet stream.

Meteor - It’s a shooting star. The brief streak of light as an object from space plunges into the Earth's atmosphere.

MCC - Mesoscale convective complexes are long-lasting clusters of thunderstorms that can dump large amounts of rain. MCCs typically form during the afternoon and evening in the form of several isolated thunderstorms, during which time the potential for severe weather is greatest. Once they mature (normally at night)   the treat shifts to flooding dangers.

MCS - a Mesoscale Convective System  is a group of multicell storms, often accompanied by a strong squall line,  tornadoes can spin up along the squall line especially on the southern end of the line. Flash flooding is always a concern. 

Mesoscale - refers to systems from 6 to around 600 miles in size.  An example would be a squall line. 
Mesohigh -  a very small area of high pressure at the surface created by the cold heavy pool of air associated with the downdraft beneath a thunderstorm. It is usually associated with an MCS or its remnants. A will defined gust front is often seen in this situation.

Mesolow - is a small wave of low pressure that forms along a line of convergent winds (a form of low-level jet), usually in the warm sector between an exiting high and an encroaching cold front.   Under the right conditions (especially if there is favorable upper-level support), it provides a focusing mechanism for strong upward lifting of warm, humid air that forms  a small thunderstorm complex,  often accompanied with a  long lived squall line, and certainly produce severe weather along their path. on Aug 5th, 2012 a mesolow produced a tornado on long Island.

 To find out more about this click here.
Mesocyclone - A mesocyclone is the rotation in the severe thunderstorm, (typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an HP storm)). A mesocyclone is a warning that very severe weather is about to occur, they do not always produce tornadoes, but 25% to near 40% do. Baseball-sized hail, extremely strong wind gusts are also possible.

For more information go here.

Mesonet -  a regional network of observing stations (usually surface stations) that report mesoscale weather features and their associated processes.
Meteor Shower - An event when hundreds of meteors or shooting stars appear in the sky at a specific time.

Meteorite - It's a meteor that reaches the Earth's surface.
Meteorologist - A scientist who studies and predicts the weather. Meteorologists use sophisticated equipment, like Doppler radar and supercomputers, but they also rely on old-fashioned sky watching.

Meteorology - The study of the atmosphere and all its phenomena, including weather and how to forecast it.

Mist - Water droplets so small that they are floating in the air. Because mist droplets do not fall, mist is a type of fog.

Muggy - The description of warm and humid air.


National Hurricane Center - They issue watches, warnings, forecasts, and analyses of hazardous tropical weather.

National Weather Service - The federal agency that provides weather, hydrologic, and climate forecasts and warnings for the United States.

North Atlantic Oscillation Index (NAO)- The positive phase of the NAO reflects below normal heights (low pressure) over the high latitudes of the North Atlantic near Greenland. And above average heights (high pressure) over the Central North Atlantic.When the NAO is positive the  jet stream pattern becomes zonal due to the lack of blocking high pressure.. The negative phase is the opposite.  a deep trough forms over the eastern half of the US, allowing cold air to spill into the eastern US.

NHC - The national Hurricane Center, issues watches, warnings, forecasts, and analyses of hazardous tropical weather.

Nexrad - It’s the "NEXt generation weather RADar", a nationwide network of 159 Doppler radars being used by National Weather Service meteorologists to detect precipitation, to measure atmospheric motions and to issue warnings of severe weather.

Nimbus - The Latin word for "rain" used to describe a cloud or group of clouds from which rain is falling.

Nor'easter - A powerful low-pressure system that moves north along the Atlantic Coast. It’s called a Nor’easter because the coastal winds are from the northeast. Heavy rain, snow and high surf often occur.

NOAA - National Oceanic and Atmospheric Administration - an agency in the Department of Commerce that maps the oceans and conserves their living resources; predicts changes to the earth's environment; provides weather reports and forecasts floods and hurricanes and other natural disasters related to weather


Occluded Front - A combination of two fronts that form when a cold front catches up and overtakes a warm front.

Overcast - When a widespread layer of clouds covers all of the sky. There may be thin or bright spots in the cloud layer, but no openings.

Overrunning - A condition that happens when an air mass moves up and over a denser air mass on the surface. This creates low clouds, fog and steady, light precipitation.

 Ozone - A form of oxygen that has a weak chlorine odor. Ozone heats the upper atmosphere by absorbing ultraviolet from sunlight. In the troposphere, ozone is a pollutant, but in the stratosphere it filters out harmful ultraviolet radiation.


The Pacific Decadal Oscillation Index (PDO)- The PDO is a pattern of change in the Pacific Oceans climate. The PDO is detected as warm or cool sea surface temperatures (SST) in the Pacific Ocean. During the warm (positive) phase the western Pacific cools and part of the eastern Pacific warms. During the cool (negative) phase the setup is the opposite. These phases shift on a decadal time scale, usually about 20-30 years. During the positive phase , the Aleutian low is stronger (deeper) and shifts southward. This results in warmer air invading the Pacific Northwest and and Alaska, along with cooler than average temperatures in Mexico and the Southeastern US. Winter precipitation is increased in the Southwest US, Pacific Northwest and Alaska, and decreased Canada and the Great Lakes into the Northeast.

The Pacific-North American pattern (PNA)- The PNA has two phases negative and positive. The PNA effects the jet pattern over northern Pacific Ocean and North America. The negative phase features lower atmospheric heights (low pressure) near Hawaii and over the Rockies in North America. Above average heights (high pressure) Aleutian Islands and the southeastern US.  The negative phase is associated with below average temperatures over western Canada and below average temperatures across the south central and the Southeast US. During Summer the PNA has little affect on temperatures in US.

Precipitation - General name for water in any form falling from clouds. This includes rain, drizzle, hail, snow and sleet. Although, dew, frost and fog are not considered to be precipitation.

Pulse thunderstorm -  is a single cell thunderstorm (garden-variety) that is usually not very strong. But they can produce strong to severe weather ,for a short period of time.

PWAT- precipitable water, the total amount of liquid in a column of the atmosphere ( from the surface to around 300mb or 30,000 feet) if it were to all fall as rain.


Quasi-biennial Oscillation (QBO)- The QBO. Eastward phases of the QBO coincide with more sudden stratospheric warming events, a weaker Atlantic jet stream and cold winters in the Eastern US and Europe.  Westward phases of the QBO are the exact opposite.

QPF - Quantitative Precipitation Forecast, the expected amount of precipitation that will fall over a specified area.


Radar - An electronic instrument, which determines the direction and distance of objects that, reflect radio energy back to the radar site. This is what meteorologists use to see rain or snow.

Rain - Liquid precipitation in the form of water drops that falls from clouds for several hours.

Rainbow - They are one of the most common but most spectacular sky displays. Rainbows are caused by the reflection and refraction (bending) of sunlight passing through raindrops. In heavy rains a double rainbow can often be seen. The sequence of a rainbows color is red, orange, yellow, green, blue, indigo and violet.

Rain Gauge - An instrument used to measure the amount of rain that has fallen. Measurement is done in hundredths of inches (0.01").

Relative Humidity - The ratio of water vapor contained in the air compared to the maximum amount of moisture that the air can hold at that specific temperature and pressure.

Ridge - It’s an elongated area of high pressure.


Saffir-Simpson Scale - A hurricane intensity scale that relates hurricane damage to wind speeds and central air pressures.
Category 1: wind speeds 74-95 m.p.h.
Category 2: wind speeds 96-110 m.p.h.

Category 3: wind speeds 111-130 m.p.h.

Category 4: wind speeds 131-155 m.p.h.
Category 5: wind speeds over 155 m.p.h.
Seasons - The earth's position in relation to the sun is always changing. The earth spins around its axis, an imaginary line that runs between the north and south poles. One complete spin takes 24 hours, and at any moment, half of the earth is lit and warm (day), while the other half faces away from the sun (night). While it spins the earth also moves around the sun in a circle, called an orbit, and the orbit takes one year to complete. As the earth moves and spins it is tilted in one direction at an angle of 23 degrees. It stays tilted all the time as it orbits the sun, so that each area of earth receives different amounts of the sun's energy at different times of the year. This is why we have seasons.
Sea Breeze - An daytime coastal breeze that blows onshore, from the sea to the land. It is caused by the temperature difference when the surface of the land is warmer than the adjacent body of water. Predominate during the day, it reaches its maximum early to mid afternoon. It blows in the opposite direction of a land breeze.

Severe Thunderstorm - a severe thunderstorm has actually been observed by spotters or indicated on radar, and is occurring or imminent in the warning area.

The thunderstorm contains has these weather conditions, hail that is at least one inch in diameter (this used to be 3/4 of an inch),   Winds of 58 miles per hour or greater. it has nothing to do with the amount of lightning are rain accompanying the thunderstorm.

Severe Thunderstorm Warning - It’s issued to warn the public, emergency management, and other cooperating agencies when a severe thunderstorm is forecast to occur or is occurring. The warning will include where the storm was occurring, its direction of movement and the primary threat from the storm.

 Severe Thunderstorm Watch - Is issued when weather conditions are favorable for the development of severe thunderstorms. A watch does not necessarily mean that severe weather is actually occurring, only that atmospheric conditions have created a significant risk for severe weather to occur.

Severe Weather - It's any kind of destructive or life-threatening weather event. Thunderstorms that can be destructive, while tornadoes, high winds, hail, excessive rainfall and lightning can be life threatening.

 Showers - It’s just rain falling from the sky causing puddles to form on the ground.

Shear - It’s just a variation in the wind speed and/or direction over a short distance.

Shortwave - It’s basically a trough. It’s an elongated area of low pressure. These can form stormy weather.

 Sleet - Solid precipitation in the form of ice pellets form when raindrops, originating in warmer air aloft, freeze as they fall through subfreezing air near the surface of the Earth.

Sleet Warning - It’s issued when accumulations of sleet in excess of a half inch are expected. This is very rare.

Slush - It’s snow or ice on the ground that has been reduced to a soft, watery mixture by rain or warm temperatures.

Small Craft Advisory - A small craft advisory is a type of warning issued by the National Weather Service, most frequently in coastal areas. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than that which is considered gale force, usually 25-38 mph.

Snow - Precipitation that is composed of white ice crystals that fall from clouds. Snow may stick together to form snowflakes, which have a hexagonal or six-sided shape.

Snow Accumulation - The actual depth of snow on the ground at any instant. This occurs during or after a snowstorm storm.

Snow Advisory - It’s issued when a snowfall is expected to exceed 2 inches but no more than 5 inches.

Snow Flurries - Brief occurrences of very light snow, which produce little or no accumulation.

Snow Pellet - see Graupel

 Snow Showers - Brief occurrences of light to moderate snow, which could produce some snowfall accumulations.

Snowflakes - Packets of falling snow formed when at least a few ice crystals are matted together. The largest snowflakes tend to occur when temperatures are near freezing. Snowflakes have a hexagonal or six-sided shape.

Snow Squall - An intense fall of accumulating snow, reducing visibility significantly and often accompanied by increased winds.

Synoptic scale - refers to systems from 130  to over 1000 miles in size. Examples of this scale are pressure systems and fronts.

Storm-scale - refers to systems on the size  of individual thunderstorms.

Soft Hail- see Graupel.

SPC- The National Storm Prediction  Center, provide timely and accurate forecasts and watches for severe thunderstorms and tornadoes over the contiguous United States. The SPC also monitors heavy rain, heavy snow, and fire weather events across the U.S. and issues specific products for those hazards.

Sprinkle - A very light shower of rain just barely wetting the ground.

Squall Line - A line of thunderstorms sometimes several hundred miles long that can produce strong thunderstorms and sometimes severe weather.

Stable Air - Air that is colder than its surroundings and is resistant to upward movement.

Stationary Front - A boundary between two air masses that more or less doesn’t move, but some stationary fronts can wobble back and forth for several hundred miles a day.

Storm - Any disturbed state of the atmosphere that creates unpleasant weather like rain, lightning, thunder, hail, snow, sleet, and freezing rain.

Storm Relative Mean Radial Velocity - This is the same as the Base Radial Velocity , but with the mean motion of the storm subtracted out. This product is available for four radar "tilt" angles, 0.5°, 1.45°, 2.40°, and 3.35°.

Storm Total Precipitation - The Storm Total Precipitation image is of estimated accumulated rainfall, continuously updated, since the last one-hour break in precipitation. This product is used to locate flood potential over urban or rural areas, estimate total basin runoff and provide rainfall accumulations for the duration of the event.
Stratus Clouds - Low-lying, gray and sheet like clouds that often produce drizzle. Stratus clouds are a principle cloud type.

Strato - A prefix to cloud-type names for clouds generally found low in the atmosphere.

Sublimation - The process of a solid (ice) changing directly into a gas (water vapor), or water vapor changing directly into ice, at the same temperature, without ever going through the liquid state (water).

Supercell - A severe thunderstorm whose updrafts and downdrafts are in near balance for several hours. Supercells often produce large hail and tornadoes.


Temperature - The measurement of how hot or cold something is.

Thermometer - The instrument that measures temperature.

Thunder - The explosive sound of air expanding as it is heated by lightning.

Thunderstorm - A storm produced by a cumulonimbus cloud and always has lightning and thunder. Rain, hail and high winds may or may not occur.

 To see more on thunderstorms click here.

Tide - The regular rise and fall of the Earth's oceans caused by the actions of the moon's and sun's gravitation acting on the rotating Earth.

Tidal Range - The difference in water level between high tide and low tide at a given place.

Tornado - a tornado is a vortex of air extending upward from the surface  into a cloud base that has deep moist convection, that is intense enough at the surface to cause damage. They can appear suddenly without warning and can be invisible until dust and debris are picked up.

You can find out more about tornadoes here.

Tornado Warning - It’s issued to warn the public, emergency management, and other cooperating agencies when a tornado is forecast to occur or is occurring. The warning will include where the storm was occurring and where it’s expected to travel.

Tornado Watch - It’s issued when conditions are favorable for the development of tornadoes.

Tornado Alley - The portion of the United States where tornadoes occur most frequently. Tornado alley is between the Plains area from the Rocky Mountains on the west to the Appalachian Mountains on the east.

Training - storm after storm moves over the same area, producing heavy rainfall.

Trade Winds - Winds which blow from tropical high pressure belts toward the equatorial region of low pressure. In the Northern Hemisphere, the trade winds blow from the northeast.

Transpiration - The process by which water in plants is transferred as water vapor to the atmosphere.

Tropical Storm - It’s a low-pressure disturbance that forms over warm tropical ocean waters. In the United States, a tropical storm has winds between 39-73 m.p.h.

Tropical Depression - It’s a low-pressure disturbance that forms over warm tropical ocean waters and produces winds of 38 m.p.h. or less.

Troposphere - It’s the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and 99% of its water vapor and aerosols. Day to day weather occurs in the troposphere.

Trough - It’s an elongated area of low pressure.


Unstable Air - Air that is warmer than its surroundings and tends to rise, leading to the formation of clouds and precipitation.


Veering Wind - A wind that changes its direction in a clockwise motion. For example, a west wind changing to a northwest wind.

Virga - Rain or snow that falls from a cloud but evaporates before it reaches the ground.

Visibility - The greatest distance that is possible for a person to see with their eyes. When fog occurs, a persons visibility is lowered.


Wall Cloud - It’s an area of clouds that extends underneath a thunderstorm. If a wall cloud rotates, it might form a tornado.

Warm Front - The boundary between two air masses, one cool and the other warm, moving so that the warmer air replaces the cooler air.

Warning - A forecast issued by the National Weather Service indicating that a specific weather event is actually occurring.

Watch - A forecast issued by the National Weather Service indicating that conditions are favorable for a particular weather hazard.

Water Vapor - It’s a gas in the atmosphere. There is very little of it in the air. Water vapor is only 1 to 4% of the atmosphere, but without it we would have no clouds, rain, or snow. Water vapor is one of the greenhouse gases, which help to trap the earth's heat.

Waterspout - A tornado occurring over water.

Weather - It describes the condition of the air at a particular time and place. Weather also tells how the air moves (wind) and describes anything it might be carrying such as rain, snow or clouds. Thunder, lightning, rainbows, haze and other special events are all part of weather.

Whiteout - It results from extreme blizzard conditions in which blowing snow or falling snow reduces visibility so that the sky, air, and ground becomes indistinguishable. Everything appears white and can be extremely dangerous for drivers.

Wind - The movement of air relative to the surface of the earth. It’s considered to be severe if 58 mph. or greater. Hurricane winds are 74 mph or greater and the highest tornado winds are about 310-320 mph m.p.h.

Wind Advisory - An advisory from the National Weather Service when the winds are between 29-38 m.p.h. lasting more than one hour, or when wind gusts are between 44-57 m.p.h.

Wind Chill - It’s the ‘feel like’ temperature on a cold day when you factor in the winds.

Wind Chill Factor - It’s a number that expresses the cooling effect of moving air at different temperatures. Only air temperature and wind speed is used in the calculation of wind chill temperatures. A wind chill temperature of 30 degrees below zero or colder on exposed skin can cause frostbite in a very short period of time.

Windchill temperature - is a unit of measurement to describe the wind chill factor.

Windchill temperature is a measure of the combined cooling effect of wind and temperature

The wind chill temperature is calculated using the following formula:

Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)
Where: T = Air Temperature (F)
V = Wind Speed (mph)
^ = raised to a power (exponential)

Wind Chill Advisory - It’s issued when the wind chill is low enough that it poses a threat to human health and life. As a general rule, the threshold for potentially dangerous wind chill conditions is about -20°F

Wind Chill Warning - Issued for dangerous, life-threatening wind chills, The exact definition varies from state to state, and a warning is used to express more severe conditions than an advisory

Windward Side - The side of an object that is facing into the direction that the wind is coming from.

Winter Storm Warning - It’s issued when hazardous winter weather is occurring or is likely over a specific area. Hazardous winter weather includes heavy snows, blizzards, ice storms, freezing rain, freezing drizzle and sleet.

Winter Weather Advisory - It’s issued for winter weather situations that could lead into hazardous conditions.

WSR-88D (Weather Surveillance Radar) is a Doppler radar, introduced in 1988. It is the type of radar display you see on your local weather report on TV.

 you can find out more about this here.
Info on Dual Pol radar can be found here

Zonal Flow - It’s when the winds in the upper levels of the atmosphere blow from coast to coast with little or no deviation. In other words, the jet stream creates a straight line. For North America a zonal flow is normally west to east.
I will add more to this from time to time. But these are the most common terms you will hear. I encourage you to bookmark this page.