Flood Watches and Warnings

WATCH                     

Severe weather is possible within the designated watch area. BE ALERT!

WARNING               

Severe weather has been reported or is imminent. TAKE ACTION IMMEDIATELY

WATCHES and WARNINGS are issued for main stem river flooding and flash flooding. A WATCH implies that people should be alert for the possibility of flooding or flash flooding, and have a plan of action in case rising waters threaten. When a WARNING is issued by the National Weather Service, this means that a flooding or flash flooding is occurring or imminent. People in the flood plain of a main stem river or in flash flood prone areas are expected to take action to protect life and property when the term WARNING is used. 

The following is a list of watches, warnings and advises that the NWS issues and the criteria used for issuing them:

FLOOD WATCH

Indicates flooding of main stem rivers is a possibility in or close to the watch area. Those living in the flood plain are urged to be ready to take action if a flood warning is issued or in flooding is observed. This product is issued within 36 hours of the possible flood event.

FLOOD WARNING

Issued to warn the public that flooding is occurring or is imminent along one or more main stem river(s). Heavy rain over a widespread area can lead to main stem river flooding depending on initial river conditions and degree of soil saturation.

FLASH FLOOD WATCH

Indicates that flash flooding is a possibility in or close to the watch area. Those in the affected area are urged to be ready to take action if a flash flood warning is issued or if flooding is observed.

FLASH FLOOD WARNING

Signifies a dangerous situation (threat to life and/or property) where rapid flooding (less than six hours after causative event) of rivers, small stream, or urban areas is imminent or is occurring. Very heavy rain that falls in a short time period can lead to flash flooding, depending on local terrain, ground cover, degree of urbanization, degree of man-made changes to river banks, soil saturation, and initial river conditions.

URBAN AND/OR SMALL STREAM FLOOD ADVISORY

Alerts the public to flooding which is generally only an inconvenient (not life-threatening) to those living in the affected area. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas. This product is also used if small rural or urban streams are expected to reach or exceed bank-full.

Source:

http://www.cityofnapa.org/Departments/Public_Works/WebPages/Weather/watches.htm