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Difference Between Watch, Warning, And Advisory
The map will show all Watches, Warnings, and Advisories issued both by the Storm Prediction Center and the National Weather Service. It is very important to know the difference because not all of them require immediate action, but preparation.
Issued by the Storm Prediction Center in Norman, Oklahoma. A Watch typically comes in the form of Tornado or Severe Thunderstorm and can include multiple counties and can last for up to 8 hours. These are issued well-ahead of any thunderstorm development to indicate that conditions are favorable for thunderstorms that could reach severe limits. If conditions are met, some thunderstorms could produce tornadoes.
Local National Weather Service offices can also issue Flood Watches in the form of Flash Flood or Areal Flood. A Flash Flood Watch indicates that heavy amounts of rainfall are expected but not necessarily immediately occurring. Areal Flood Watches are issued to indicate that nuisance flooding may occur in low-lying areas such as ditches and along streams.
Advisories are issued by the National Weather Service to indicate an "inconvenience". The most common Advisory we see is a Significant Weather Advisory for strong thunderstorms, which indicates that the storm may have a lot of lightning, strong winds, and small hail but should not be considered a direct threat to life or property, although it is advised to seek shelter until the storm passes or diminishes.
Advisories can also be issued for events such as patchy dense fog, which indicates visibilities may drop below 1/3 of a mile, which can make driving hazardous. When a Dense Fog Advisory is issued it is advised to plan to reach your destination earlier and leave more room between you and the vehicle in front of you and plan for sudden drops in visibilities.
Warnings are issued by your local National Weather Service office to indicate that a life-threatening storm or hazard is expected to occur or is already moving in your direction. Warnings come with several different labels, so here is a breakdown of all of them:
These are issued when Doppler radar indicates rotation within a thunderstorm showing the storm could produce a tornado within the next few minutes. They are also issued if there is ground confirmation of a tornado on or near the ground. Tornado Warnings are generally issued about 15 minutes in advance of the storm arriving in your community, and they typically do not last longer than 30 minutes.
Severe Thunderstorm Warning
These are issued when Doppler radar detects winds of 58 Miles Per Hour or more, or quarter size hail (0.75"), or if there have been reports of damage within a thunderstorm. Winds of this magnitude and hail of this size can easily bring down trees causing power outages and damage to vehicles and outbuildings. The immediate action is to get inside and stay away from windows and plan for power outages. Severe Thunderstorm Warnings are issued up to 15 minutes of the storm arriving at a particular location and can last up to an hour.
Flash Flood Warning
These are issued when Doppler radar has detected 2 inches of rainfall over the past hour for a particular area. Rainfall of this rate will lead to excessive runoff from streams and roadways and cause life-threatening travel conditions. The immediate action is to drive slowly and if you see a large body of water on a roadway. remember the phrase TURN AROUND, DON'T DROWN. Flash Flood Warnings are issued when flash flooding is already occurring or is expected to begin shortly, and they can last for up to 5 hours.