Severe Thunderstorm Warning

Ladies and gentlemen, residents and visitors alike, attention please! We interrupt your regular programming to bring you a crucial message of utmost importance. Brace yourselves, for Mother Nature is unleashing her fury upon us! A severe thunderstorm warning has been issued for our area, and it’s imperative that we all heed this warning with the utmost seriousness.

Picture this: dark, ominous clouds swirling ominously overhead, crackling with electricity. The air is heavy with anticipation, charged with the energy of an impending tempest. Thunder rumbles in the distance, a harbinger of the tumult to come. Lightning streaks across the sky, illuminating the landscape in a dazzling display of nature’s power.

But this is no ordinary thunderstorm, my friends. This is a severe thunderstorm, a force to be reckoned with. Strong winds gusting at alarming speeds, torrential rainfall flooding the streets, and hail pelting down with relentless force. In its wake, this tempest leaves a trail of destruction, uprooting trees, knocking down power lines, and causing havoc wherever it roams.

Now is not the time for complacency or indifference. Now is the time for vigilance and preparedness. Take shelter immediately, preferably in a sturdy building away from windows. Secure any loose objects outdoors, and stay tuned to local news and weather updates for further instructions.

A severe thunderstorm warning, often indicated by the SAME (Specific Area Message Encoding) code SVR, serves as a crucial public alert for imminent severe weather conditions. This warning is disseminated by meteorological agencies worldwide, triggered when severe thunderstorms are either detected by advanced Doppler weather radar systems, spotted by trained weather observers, or reported by various authorities or members of the public.

What sets a severe thunderstorm warning apart from a watch is its specificity and urgency. While a watch signals the potential for severe weather conditions over a broader area and time frame, a warning is a direct signal that severe weather is imminent and likely to impact a specific area within a short time frame, typically within the hour. This pinpoint accuracy enables individuals and communities to take immediate action to protect themselves and their property.

The hazards associated with severe thunderstorms are varied and potentially dangerous. Large hail, high winds, and torrential rainfall leading to flash flooding are among the primary threats. These phenomena can cause significant damage to property, infrastructure, and crops, as well as pose risks to human safety and well-being.

It’s important to note that the criteria for issuing a severe thunderstorm warning can vary from one country to another, reflecting differences in meteorological conditions, infrastructure, and risk management strategies. However, regardless of the specific criteria, the overarching goal remains consistent: to provide timely and accurate information to enable individuals, communities, and authorities to prepare for and respond to severe weather events effectively.

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Definition of Severe Thunderstorm Warning

A severe thunderstorm warning is a specific public alert indicating that the warned area faces imminent danger from severe weather conditions associated with thunderstorms. These conditions typically include hail or wind speeds meeting warning criteria, as well as potential hazards from lightning and hydrological impacts generated by the storm cell.

Severe thunderstorms have the potential to produce tornadoes without warning, making them particularly hazardous weather phenomena. While not all severe thunderstorms result in tornadoes, they can still inflict significant damage through serious straight-line wind gusts, comparable to those of a lower-category tornado or even a hurricane. These wind gusts can cover a much broader area than the relatively narrow path of a tornado, posing risks to a larger population and a wider expanse of infrastructure.

When a tornado is detected on radar or visually sighted, a tornado warning may be issued either concurrently with or in replacement of an existing severe thunderstorm warning. Typically, a severe thunderstorm watch or tornado watch, or their regional equivalents, precede a warning, providing advanced notice of potentially hazardous weather conditions.

In the event of a tornado warning, based on Doppler weather radar, it signifies that strong rotation has been detected within a thunderstorm, indicating an increased likelihood of tornado formation. If a thunderstorm is producing only weak rotation, it may warrant a severe thunderstorm warning, but the public will be advised to monitor the storm closely for any signs of intensification in the near future. This proactive approach enables individuals and communities to stay informed and take appropriate precautions to mitigate the risks posed by severe thunderstorms and tornadoes.

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Regional Basis and Criteria: United States

In the United States, severe thunderstorm warnings are issued by the National Weather Service (NWS) to alert the public of imminent severe weather conditions. The NWS defines a severe thunderstorm as meeting one or more of the following criteria:

Large hail: One inch (2.5 cm) in diameter or larger.
Surface wind speeds: 58 mph (50 knots; 93 km/h) or greater.
Tornado activity.

Prior to January 2010, the hail size required for a thunderstorm to be considered severe was 0.75 inches (1.9 cm). However, due to public complacency resulting from frequent issuances of severe thunderstorm warnings and studies indicating that hail did not typically cause significant damage until it reached one inch in diameter, the criteria for hail size was upgraded.

Severe thunderstorm warnings are issued by NWS local Weather Forecast Offices, which utilize WarnGen software integrated into the Advance Weather Interactive Processing System (AWIPS) to generate the warning statement. These warnings are then disseminated through various communication channels including:

Media outlets
Various agencies
Internet platforms
NOAA satellites
NOAA Weather Radio
Emergency Alert System (EAS) to local broadcast media
Wireless Emergency Alerts (WEA) for cellular phones

Local NWS forecast offices outline warnings for tornadoes and severe thunderstorms using polygonal shapes for map-based weather hazard products. These warnings are distributed to various platforms including the main agency website, individual forecast office websites, and the Storm Prediction Center. Additionally, open-source APIs are available for free use by public weather websites and mobile apps.

In NWS text products, warnings are typically illustrated by individual counties, parishes, or other county-equivalent jurisdictions, presented in list format if covering multiple jurisdictions. Previously, warnings were issued on a per-county basis prior to October 2007.

Severe weather alert displays used by some television stations often highlight severe thunderstorm warnings with a yellow or orange polygon or filled county/parish/equivalent jurisdiction outline, aiding in visual recognition of the warned areas.

The National Weather Service (NWS) in the United States employs various levels of severity and additional warnings to enhance the effectiveness of severe thunderstorm warnings and keep the public informed about potential dangers. These additional warnings and enhancements include:

Particularly Dangerous Situation (PDS) Warnings: These warnings are issued when an extremely intense severe thunderstorm is expected to impact a densely populated area. The criteria for issuing a PDS warning include the presence of very large hailstones and/or intense straight-line winds capable of causing major structural damage, especially to roofs, windows, siding, and structures of poor construction such as outbuildings and mobile homes. Severe injury or even death to people and animals exposed outdoors due to hail-induced blunt trauma or wind-generated debris is also a consideration.
Severe Thunderstorm Emergency: This statement, although unofficial, is the highest and most urgent level relating to non-tornadic severe thunderstorms. It is an extension of the tornado emergency statements issued to warn of a violent tornado impacting populated areas.
Safety Precaution Action Statements: In regions where tornadic activity is a concern, local NWS forecast offices may include safety precaution action statements in severe thunderstorm warnings. These statements advise the public to stay informed about possible tornado development and any tornado warnings that may be issued, especially if a tornado watch is already in effect.

In March 2012, the NWS implemented a multi-tier Impact Based Warning (IBW) system to notify the public and emergency management officials of the severity of specific severe weather phenomena. As part of this system, severe thunderstorm warnings and associated Severe Weather Statements provide updated storm information, including event tags at the bottom of the product text. These event tags provide summarical estimates of straight-line wind speeds, hail size, and indicate possible tornadic development.

The threat indicators in the IBW system consist of three coded taglines:

Tornado: Indicates the potential for tornado formation within the severe thunderstorm.
Hail: Indicates the estimated size of hail being produced by the storm.
Wind: Indicates the estimated speed of wind gusts produced by the storm.

Since July 28, 2021, the NWS has incorporated categorical damage threat indicators for higher-end hail and/or wind events. These indicators include “Considerable” for hail of 1.75 inches or larger and/or winds at or above 70 mph, and “Destructive” for hail of 2.75 inches or larger and/or winds at or above 80 mph. These warnings are intended to further explain to the public the dangers posed by severe thunderstorms, especially those capable of producing massive hailstones and damaging winds equivalent to hurricanes or tornadoes.

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Severe Thunderstorms in Canada

In Canada, severe thunderstorms are characterized by several key indicators: wind gusts exceeding 90 km/h (56 mph), hail with a diameter larger than two centimetres (0.79 in), intense rainfall rates exceeding 50 millimetres (2.0 in) in one hour or 75 millimetres (3.0 in) in three hours, and the presence of tornadoes. These phenomena pose significant risks to communities, infrastructure, and the safety of individuals.

Warning System: Environment and Climate Change Canada plays a crucial role in issuing severe thunderstorm warnings through its regional offices, which are part of the Meteorological Service of Canada. These regional offices are strategically located in Vancouver, Edmonton, Winnipeg, Toronto, Montreal, and Dartmouth. The warnings are specifically tailored for designated municipalities and census subdivisions, ensuring that communities receive timely and accurate information about impending severe weather events.

Dissemination of Warnings: To effectively communicate warnings to the public, various channels are utilized. These include broadcast and online media outlets, as well as Weatheradio Canada. Additionally, depending on the severity of the storm and the discretion of regional offices, the National Public Alerting System (Alert Ready) may be activated. This system, known as Système national d’alertes à la population in French, ensures that warnings reach a broader audience by distributing alerts to local broadcast media and cellular phones. Furthermore, provincial alerting systems, such as Alberta Emergency Alert and SaskAlert, may also be engaged to enhance the dissemination of warnings at a local level.

Regional Considerations: It’s important to note that severe thunderstorm warnings may encompass areas adjacent to the immediate path of a storm. This proactive approach acknowledges the potential for severe weather impacts beyond the direct trajectory of the thunderstorm. By extending warnings to these adjacent areas, authorities aim to minimize the risk of harm to communities and facilitate preparedness measures.

Conclusion: The effective management of severe thunderstorm warnings in Canada underscores the importance of proactive risk mitigation and public safety initiatives. Through a coordinated effort involving meteorological expertise, advanced warning systems, and widespread dissemination channels, authorities strive to safeguard lives and property from the impacts of severe weather events.

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Severe Thunderstorms in the United Kingdom

In the United Kingdom, severe thunderstorms are characterized by specific meteorological criteria, primarily involving hail and straight-line winds. The following elaborates on the definition, warning system, and issuance of severe thunderstorm warnings in the UK:

Definition: A severe thunderstorm in the UK is officially defined by the presence of hail exceeding two centimetres (0.79 in) in diameter and straight-line winds surpassing 89 km/h (48 kn; 55 mph). These criteria indicate the potential for significant impacts on infrastructure, property, and public safety.

Warning System: The Met Office, the UK’s national weather service, plays a central role in issuing severe thunderstorm warnings. These warnings are not explicitly labeled as “severe thunderstorm warnings” but are instead incorporated into general-purpose weather warning products. These warnings are disseminated through the National Severe Weather Warning Service (NSWWS), which classifies warnings based on severity using a color-coded system. Warnings are typically categorized as yellow, amber, or red, depending on the severity of the anticipated storm impacts and the proximity to the expected onset of severe weather conditions.

Dissemination of Warnings: The issuance of severe thunderstorm warnings and other weather alerts involves widespread dissemination through various channels. This includes broadcast media, online platforms, social media, and dedicated weather apps. By utilizing multiple communication channels, the Met Office aims to ensure that the public receives timely and accurate information about impending severe weather events, enabling individuals and communities to take appropriate precautionary measures.

Severity and Proximity Considerations: The color-coded warning system employed by the NSWWS takes into account both the severity of the impending storm and its proximity to the time of expected onset. This allows for a nuanced assessment of the potential impacts and facilitates targeted preparedness and response efforts. Depending on the severity of the situation, authorities may issue amber or red warnings, indicating a higher level of risk and the need for heightened vigilance.

Conclusion: The United Kingdom’s approach to severe thunderstorm warnings emphasizes the importance of proactive risk management and public safety initiatives. Through the integration of meteorological expertise, advanced warning systems, and effective communication strategies, authorities strive to minimize the impact of severe weather events on society and promote resilience in the face of natural hazards.

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Severe Thunderstorms in Australia

Australia experiences frequent severe thunderstorms, which can pose significant risks to life, property, and infrastructure. Here’s an elaboration on the definition, warning system, and issuance of severe thunderstorm warnings in Australia:

Definition: In Australia, a severe thunderstorm is officially defined by the presence of several key meteorological indicators, including damaging winds exceeding 90 km/h (49 kn; 56 mph), large hail measuring two centimetres (0.79 in) or larger in diameter, heavy rainfall, and the potential for flash flooding. These criteria highlight the potential for widespread impacts and the need for heightened vigilance.

Warning System: The Bureau of Meteorology (BOM), Australia’s national weather agency, is responsible for issuing severe thunderstorm warnings. These warnings are disseminated through regional offices located in Melbourne Docklands, Adelaide, Darwin, Perth, and Brisbane. The BOM employs a comprehensive approach to warning issuance, aiming to provide timely and accurate information to the public and emergency management agencies.

Types of Warnings: BOM-issued severe thunderstorm warnings in Australia are categorized into two main types: broad-based warnings and detailed warnings. Broad-based warnings cover expected impacts within a designated weather reporting area, providing general guidance on potential hazards such as damaging winds, large hail, heavy rainfall, and flash flooding. Detailed warnings are issued when a thunderstorm is within the range of weather-watch radar and include a map depicting the location of existing thunderstorms and the forecast direction of movement for up to 60 minutes. This detailed information enables individuals and communities to take specific actions to mitigate the impacts of severe weather events.

Dissemination of Warnings: Severe thunderstorm warnings issued by the BOM are disseminated through various communication channels to ensure broad accessibility. These channels include broadcast media, online platforms, social media, dedicated weather apps, and the BOM’s official website. Additionally, the BOM collaborates with emergency management agencies and other stakeholders to facilitate the timely dissemination of warnings and promote community preparedness and resilience.

Conclusion: Australia’s approach to severe thunderstorm warnings underscores the importance of proactive risk management and effective communication in mitigating the impacts of extreme weather events. Through the coordination of meteorological expertise, advanced warning systems, and multi-channel dissemination strategies, authorities aim to enhance public safety and reduce the vulnerability of communities to severe weather hazards.

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Severe Thunderstorms in New Zealand

New Zealand, known for its stunning landscapes, also experiences severe thunderstorms that can pose risks to its residents and infrastructure. Let’s delve into the definition, warning system, and dissemination of severe thunderstorm warnings in New Zealand:

Definition: In New Zealand, the Meteorological Service of New Zealand, commonly referred to as MetService (Te Ratonga Tirorangi in Māori), defines a severe thunderstorm by several key meteorological parameters. These include large hail with a diameter of 20 millimetres (2.0 cm; 0.79 in), damaging winds exceeding 110 km/h (59 kn; 68 mph), heavy rainfall rates of at least 25 millimetres (0.98 in) per hour, and the presence of tornadoes producing winds above 116 km/h (63 kn; 72 mph), rated F1 or stronger on the Fujita Scale. These criteria help identify thunderstorms with the potential for significant impacts on communities and infrastructure.

Warning System: MetService issues severe thunderstorm warnings to alert regions expected to experience severe weather phenomena meeting regional criteria. The warnings are generated using the Common Alerting Protocol (CAP), ensuring a standardized format for warning statements. This allows for efficient dissemination of critical information to the public and emergency management agencies.

Dissemination of Warnings: Severe thunderstorm warnings in New Zealand are disseminated through various communication channels to reach a wide audience. These channels include terrestrial television and radio stations, online media platforms, mobile apps, and SMS messaging through the Emergency Mobile Alert (EMA) system. Additionally, if a tornado has been sighted or indicated by radar within the warned area during the severe thunderstorm warning’s duration, civil defense sirens may be activated within the affected region to inform people outdoors of the approaching tornado threat. This multi-channel approach aims to ensure that individuals receive timely and accurate information to take appropriate precautions and ensure their safety.

Conclusion: New Zealand’s approach to severe thunderstorm warnings emphasizes the importance of proactive risk management and public safety initiatives. Through the integration of meteorological expertise, advanced warning systems, and effective communication strategies, authorities aim to minimize the impact of severe weather events on society and enhance community resilience in the face of natural hazards.

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Severe Thunderstorms in the Philippines

The Philippines, situated in a tropical climate zone, experiences severe thunderstorms that can result in significant hazards to life and property. Here’s an elaboration on the definition, warning system, and dissemination of severe thunderstorm advisories in the Philippines:

Definition: In the Philippines, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) defines a severe thunderstorm by several meteorological parameters. These include strong winds, large hail, torrential rainfall, tornadoes, flash flooding, and/or landslides. These criteria encompass a range of severe weather phenomena that can pose risks to communities and infrastructure.

Warning System: PAGASA, through its regional services divisions, plays a critical role in issuing thunderstorm advisories to alert regions and/or provinces expected to experience severe weather phenomena meeting regional criteria within a period of two hours. These advisories provide essential information to communities and authorities, allowing them to prepare and respond effectively to impending severe weather events.

Dissemination of Advisories: Thunderstorm advisories issued by PAGASA are disseminated to the public through various communication channels to ensure broad accessibility. These channels include terrestrial television and radio outlets, online media platforms, and SMS messages through the National Disaster Risk Reduction and Management Council’s Emergency Cell Broadcast System. This multi-channel approach aims to reach a wide audience and ensure that individuals receive timely and accurate information to take appropriate precautions and ensure their safety.

Community Preparedness: Given the vulnerability of the Philippines to severe weather events, community preparedness and resilience are emphasized as essential components of disaster risk reduction efforts. Through public awareness campaigns, community drills, and capacity-building initiatives, authorities aim to empower individuals and communities to mitigate the impacts of severe thunderstorms and other natural hazards.

Conclusion: The Philippines’ approach to severe thunderstorm advisories underscores the importance of proactive risk management and community resilience in mitigating the impacts of extreme weather events. Through the coordination of meteorological expertise, advanced warning systems, and effective communication strategies, authorities strive to enhance public safety and reduce the vulnerability of communities to severe weather hazards.

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Criteria in various countries

Here’s a tabular representation of severe thunderstorm criteria in various countries:

Country	Tornado Criteria	Minimum Hail Size	Minimum Wind Speed	Minimum Rainfall Rate per Hour	Source
United States	See Tornado Warning	1 inch (25 mm)	58 miles per hour (93 km/h)	See Flash Flood Warning	[6]
Canada	See Tornado Warning	20 millimetres (0.79 in)	90 kilometres per hour (56 mph)	50 millimetres (2.0 in)	[14]
Australia	All	20 millimetres (0.79 in)	90 kilometres per hour (56 mph)	“Conducive to flash flooding”	[22]
New Zealand	F1 or stronger	20 millimetres (0.79 in)	110 kilometres per hour (68 mph)	25 millimetres (0.98 in)	[23]
Germany	All	15 millimetres (0.59 in)	105 kilometres per hour (65 mph)	20 millimetres (0.79 in)	[24]
Mexico	All	5 millimetres (0.20 in)	89 kilometres per hour (55 mph)	20 millimetres (0.79 in)	[25][26][27]
United Kingdom	All	20 millimetres (0.79 in)	55 miles per hour (89 km/h)	“Conducive to flash flooding”	[15]

This table provides a comparative overview of the criteria used by different countries to define severe thunderstorms, including thresholds for tornadoes, hail size, wind speed, and rainfall rate.

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Examples of severe thunderstorm warnings

Severe thunderstorm warnings are issued by meteorological agencies to alert the public about imminent severe weather conditions that may include damaging winds, large hail, heavy rainfall, flash flooding, and sometimes tornadoes. Here are a few examples of severe thunderstorm warnings:

Tornado Warning: This warning is issued when a severe thunderstorm is capable of producing a tornado or when a tornado has been sighted by spotters or indicated by radar. It advises people to take immediate shelter and seek safety in a sturdy building or underground shelter.
Severe Thunderstorm Warning: This warning is issued when a severe thunderstorm is detected or anticipated to produce damaging winds exceeding a certain threshold, large hail, and/or heavy rainfall leading to flash flooding. It advises people to stay indoors, away from windows, and secure loose objects that could become projectiles in strong winds.
Hail Warning: In areas prone to hailstorms, meteorological agencies may issue specific hail warnings when large hail is expected to accompany severe thunderstorms. This warns residents to protect their vehicles, move indoors, and take precautions to avoid injury from falling hailstones.
Flash Flood Warning: When heavy rainfall is expected to cause rapid flooding of rivers, streams, and low-lying areas, a flash flood warning is issued. This warns people to avoid flooded areas, refrain from driving through flooded roadways, and seek higher ground if in a flood-prone area.
Tornado Watch: While not a warning, a tornado watch is issued when conditions are favorable for the development of tornadoes in a particular area. It alerts residents to be vigilant and prepared to take action if severe weather escalates.
Severe Thunderstorm Watch: Similar to a tornado watch, a severe thunderstorm watch is issued when conditions are favorable for the development of severe thunderstorms, including damaging winds, large hail, and heavy rainfall. It advises residents to stay informed and prepared for potential severe weather.

These warnings are typically disseminated through various channels, including broadcast media, weather radio, online platforms, mobile apps, and emergency alert systems, to ensure that the public receives timely and accurate information to stay safe during severe weather events.

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FAQs

What is a severe thunderstorm?
- A severe thunderstorm is a storm that produces damaging winds, large hail, heavy rainfall, and sometimes tornadoes.
How is a severe thunderstorm warning issued?
- Severe thunderstorm warnings are issued by meteorological agencies based on observed or anticipated severe weather conditions.
What should I do during a severe thunderstorm warning?
- Seek shelter indoors, away from windows, and avoid outdoor activities until the storm passes.
What is the difference between a severe thunderstorm watch and warning?
- A watch means conditions are favorable for severe thunderstorms, while a warning means severe weather is imminent or occurring.
How can I stay informed about severe weather warnings?
- Stay tuned to local weather forecasts, download weather apps, and have a NOAA weather radio for alerts.
What should I do if I’m driving during a severe thunderstorm?
- Pull over to a safe location away from trees and power lines, and wait for the storm to pass.
Can severe thunderstorms cause power outages?
- Yes, strong winds and lightning associated with severe thunderstorms can cause power outages.
How can I protect my home during a severe thunderstorm?
- Secure loose outdoor items, close windows and doors, and consider installing surge protectors.
Is it safe to use electronics during a thunderstorm?
- It’s best to unplug electronic devices during a thunderstorm to avoid damage from power surges.
What should I do if I’m caught outdoors during a thunderstorm?
- Seek shelter indoors if possible, and if not, avoid tall objects and seek low-lying areas away from trees.
How can I prepare for a severe thunderstorm?
- Have an emergency kit, including water, food, flashlights, and a first aid kit, and have a plan for where to seek shelter.
Can severe thunderstorms lead to flooding?
- Yes, heavy rainfall from severe thunderstorms can cause flash flooding in low-lying areas.
Are pets affected by thunderstorms?
- Some pets may be frightened by thunderstorms, so it’s best to keep them indoors during severe weather.
How long do severe thunderstorms typically last?
- The duration of a severe thunderstorm can vary, but they typically last for 30 minutes to an hour.
Can severe thunderstorms produce tornadoes?
- Yes, severe thunderstorms can produce tornadoes, especially in areas with favorable atmospheric conditions.
What is the difference between a tornado and a funnel cloud?
- A tornado is a rotating column of air that reaches the ground, while a funnel cloud is a rotating column of air that hasn’t touched the ground yet.
Is lightning always associated with severe thunderstorms?
- Lightning is common in severe thunderstorms, but not all lightning-producing storms are considered severe.
How can I report severe weather to authorities?
- Contact your local meteorological agency or emergency management office to report severe weather observations.
Can severe thunderstorms occur at night?
- Yes, severe thunderstorms can occur at any time, including during the night.
What should I do after a severe thunderstorm passes?
- Check for any damage to your property, and stay informed about any additional weather warnings or advisories.