Severe Weather

Thunderstorms, Tornadoes, and Lightning  - Nature’s most violent storms.

Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. Despite their small size, ALL thunderstorms are dangerous! Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classified as severe.

Tornadoes - Although tornadoes occur in many parts of the world, they are found most frequently in the United States.....

Union City, Oklahoma tornado. Learn more...

• A tornado is a violently rotating column of air extending from a thunderstorm to the ground.
• Tornadoes cause an average of 70 fatalities and 1,500 injuries in the U.S. each year..
• The strongest tornadoes have rotating winds of more than 250 mph.
• Tornadoes can be one mile wide and stay on the ground over 50 miles.
• Tornadoes may appear nearly transparent until dust and debris are picked up or a cloud forms within the funnel. The average tornado moves from southwest to northeast, but tornadoes have been known to move in any direction.
• The average forward speed is 30 mph but may vary from nearly stationary to 70 mph.
• Waterspouts are tornadoes which form over warm water. They can move onshore and cause damage to coastal areas.

Lightning...

• Causes an average of about 60 fatalities and 300 injuries each year.
• Lightning occurs in all thunderstorms; each year lightning strikes the United States 25 million times.
• The energy from one lightning flash could light a 100-watt light bulb for more than 3 months.
• Most lightning fatalities and injuries occur when people are caught outdoors in the summer months during the afternoon and evening.
• Lightning can occur from cloud-to-cloud, within a cloud, cloud-to-ground, or cloud-to-air.
• Many fires in the western United States and Alaska are started by lightning.
• The air near a lightning strike is heated to 50,000°F--hotter than the surface of the sun!
• The rapid heating and cooling of the air near the lightning channel causes a shock wave that results in thunder.
• When Thunder Roars, Go Indoors! - NWS lighnting safety site helps ypu learn more about lightning risks and how to protect yourself, your loved ones and your belongings. The site offers a comprehensive page of handouts, brochures, links and more.

Straight-line Winds...

• Straight-line winds are responsible for most thunderstorm wind damage.
• Winds can exceed 100 mph!
• One type of straight-line wind, the downburst, is a small area of rapidly descending air beneath a thunderstorm
• A downburst can cause damage equivalent to a strong tornado and can be extremely dangerous to aviation.
• A “dry microburst” is a downburst that occurs with little or no rain. These destructive winds are most common in the western United States

Flash Flooding...

• Is the #1 cause of deaths associated with thunderstorms...more than 140 fatalities each year
• Most flash flood fatalities occur at night and most victims are people who become trapped in automobiles.
• Six inches of fast-moving water can knock you off your feet; a depth of two feet will cause most vehicles to float.

Hail...

• Strong rising currents of air within a storm, called updrafts, carry water droplets to a height where freezing occurs.
• Ice particles grow in size, becoming too heavy to be supported by the updraft, and fall to the ground.
• Causes more than $1 billion in damage to property and crops each year.
• Large stones fall at speeds faster than 100 mph.

Multiple lightning strokes observed during night-time thunderstorm. Learn more...

The National Severe Storms Laboratory is one of NOAA's internationally known research laboratories, leading the way in investigations of all aspects of severe weather. Headquartered in Norman OK, the people of NSSL, in partnership with the National Weather Service, are dedicated to improving severe weather warnings and forecasts in order to save lives and reduce property damage.
Severe weather research conducted at NSSL has led to substantial improvements in severe and hazardous weather forecasting resulting in increased warning lead times to the public. NSSL scientists are exploring new ways to improve our understanding of the causes of severe weather and ways to use weather information to assist National Weather Service forecasters, as well as federal, university and private sector partners.

The Storm Prediction Center (SPC) is part of the National Weather Service (NWS) and the National Centers for Environmental Prediction (NCEP). The mission of the SPC is to 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.

Weather Forecast Offices of NOAA’s National Weather Service issue local Severe Thunderstorm, Tornado and Flash Flood warnings. Severe thunderstorm, tornado, and flash flood warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities.

NOAA Weather Radio is the best means to receive warnings from the National Weather Service.

The National Weather Service continuously broadcasts warnings and forecasts that can be received by NOAA Weather Radios, which are sold in many stores. The average range is 40 miles, depending on topography. Purchase a radio that has a battery back-up and a Specific Area Message Encoder feature, which automatically alerts you when a watch or warning is issued for your county or parish.

When conditions are favorable for severe weather to develop, a severe thunderstorm or tornado WATCH is issued. Weather Service personnel use information from weather radar, spotters, and other sources to issue severe thunderstorm and tornado WARNINGS for areas where severe weather is imminent. Severe thunderstorm and tornado warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities. If a tornado warning is issued for your area or the sky becomes threatening, move to your pre-designated place of safety.

Check with your local National Weather Service office or visit the Internet site to determine if your county is covered by NOAA Weather Radio. National Weather Service watches and warnings are also available on the Internet by selecting your local National Weather Service office at or by going to the National Weather Service Home Page.

Terms to know:

Tornado - A violently rotating column of air, usually pendant to a cumulonimbus, with circulation reaching the ground. It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise. On a local scale, it is the most destructive of all atmospheric phenomena

Severe Thunderstorm - A thunderstorm that produces a tornado, winds of at least 58 mph (50 knots), and/or hail at least 1 inch in diameter. Structural wind damage may imply the occurrence of a severe thunderstorm.

Flash Flood - A flood which is caused by heavy or excessive rainfall in a short period of time, generally less than 6 hours. Also, at times a dam failure can cause a flash flood, depending on the type of dam and time period during which the break occurs.

Tornado Watch: Tornadoes are possible in your area. Remain alert for approaching storms. Know what counties or parishes are in the watch area by listening to NOAA Weather Radio or your local radio/television outlets.

Severe Thunderstorm Watch: Tells you when and where severe thunderstorms are likely to occur. Watch the sky and stay tuned to know when warnings are issued.

Flash Flood Watch - Issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.

Tornado Warning: A tornado has been sighted or indicated by weather radar.

Severe Thunderstorm Warning: Issued when severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property to those in the path of the storm.

Flash Flood Warning - Issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.