Severe Weather Terminology

 

Types of Alerts

 
 

Warning — Severe weather is occurring now or is imminent and you should take protective action immediately.

Watch — Conditions are favorable for the development of severe weather. You should form a plan of action and check for updates frequently.

Advisory or Outlook — Conditions are present for the development of hazardous weather within the next 7 days. You should form a plan of action and check for updates periodically.

 

Typical Severe Weather Alerts for New Roads, LA

 

Flash Flood Warning — Issued to inform the public that flash flooding is imminent or occurring, generally within 6 hours after the causative event, when there is a rapid rise in water levels in urban areas, small drainages, or arroyos. Issued from areas as small as portions of cities to multiple parishes.

Flash Flood Watch — Issued when meteorological, soil, or hydrologic conditions indicate flash flooding is possible, or if a dam could fail and threaten life and property, but the threat does not yet appear imminent. Flash flooding would occur within 6 hours of the causative event. Issued by parish or coastal zone.

 

Flood Warning — For non-river events: Issued to inform the public that flooding will continue for several hours after the causative event has ended. In general, 6 hours after the rain has tapered to drizzle or ended, or 2 to 6 hours after the rain has ended and sunshine/clearing has begun.
For river/reservoir events: Issued when significant flooding is expected to threaten life and property from overflowing, gauged rivers or creeks. Only issued where there are gauged and proxy locations where defined flood stages exist.

Flood Watch — Non-river issuances: Issued to inform the public that current and developing weather conditions are such that there is a threat of flooding or flash flooding, but the occurrence is neither certain nor imminent.
River issuances: When a river is forecast to equal or exceed flood stage 12 to 36 hours out. Also issued to denote flood potential due to post-tropical cyclone flooding or potential dam failure.

Flood Advisory — For nuisance type flooding meeting one of the following criteria:

  • <3 feet of standing water, enough to cause minor flooding of roads, especially in poor drainage locations;

  • <6 inches of fast flowing water across roads;

  • Arroyos/streams/creeks nearing bankfull, or briefly overtopping banks, producing < 6 inches of fast flowing water

 

Excessive Heat Warning — Issued when Heat index is expected to be ≥120°F for ≥2 hours during the daytime for two consecutive days or more, with ambient nighttime temperature of ≥80°F in between. Heat area should occur over ≥½ of a zone’s area, or ≥½ of a zone’s population. Issued when conditions are generally expected to occur within 12 to 36 hours.

Excessive Heat Watch — Same conditions as with Excessive Heat Warning, above, except when conditions are possible within a 24 to 48 hour period.

Heat Advisory — Issued when Heat Index is expected to be ≥111°F for ≥2 hours during the daytime for two consecutive days or more, with ambient nighttime temperature of ≥75 in between. Heat area should cover ≥½ of a zone’s area, or ≥½ of a zone’s population. Advisories are generally issued when conditions are expected within the next 12 to 36 hours.

 

Hard Freeze Warning — Issued when ambient temperatures are expected to be ≤27°F for ≥2 hours in a 12 hour period. Values should cover ≥½ of a zone’s area, or ≥½ of a zone’s population. Generally issued within 12 to 36 hours of event occurrence.

Hard Freeze Watch — Issued when a Hard Freeze is possible, generally within the next 24 to 48 hours.

 

Freeze Warning — Issued when ambient temperatures are expected to be ≤32°F for ≥2 hours in a 12 hour period. Freezing temperatures should cover ≥½ of a zone’s area, or ≥½ of a zone’s population

Freeze Watch — Issued when a freeze is possible, generally within the next 24 to 48 hours.

 

Hurricane Warning — Issued when sustained winds, or frequent gusts ≥64 knots (74 mph), within a 12 hour period, are expected to develop within 12 to 36 hours. In cases where confidence is high, warnings may be issued out to 48 hours or longer. Sustained winds should generally occur for ≥2 hours. On Land: Should occur across ≥½ of zone area or zone population. Associated with tropical cyclones only.
Hurricane Warnings consider the storm as entity. A myriad of hazards, ranging from Storm Surge Flooding to Inland Flooding and Tornadoes on land, and very high seas with breaking waves on the ocean, often occur. The Hurricane Local Statement covers these impacts in total, but the warning itself is based on the expected wind speed threshold.

Hurricane Watch — Issued for the same conditions described in Hurricane Warning, except for the possibility of occurrence over the next 24 to 48 hours. In cases where confidence is high, watches may be issued out to 60 hours or longer.

 

Tropical Storm Warning — Issued when sustained winds, or frequent gusts between 34 and 63 knots (39 to 73 mph), within a 12 hour period, are expected to develop within 12 to 36 hours. In cases where confidence is high, warnings may be issued out to 48 hours or longer. Sustained winds should generally occur for ≥2 hours. On Land: Should occur across ≥½ of zone area or zone population. Associated with tropical cyclones only.
Tropical Storm Warnings consider the storm as entity. A myriad of hazards, ranging from Storm Surge Flooding to Inland Flooding and Tornadoes on land, and very high seas with breaking waves on the ocean, often occur. The Hurricane Local Statement covers these impacts in total, but the warning itself is based on the expected wind speed threshold.

Tropical Storm Watch — Issued for the same conditions described in Tropical Storm Warning, except for the possibility of occurrence over the next 24 to 48 hours. In cases where confidence is high, watches may be issued out to 60 hours or longer.

 

For more information about all types of alerts, see the National Weather Service’s list of definitions.