Hydrology Watch, Warning and Advisory Definitions

• Recent Watches/Warnings/Advisories for Southeast Michigan

Hydrology/Flooding Definitions

Flood Watch

Flood watches inform the public of hydrometeorological conditions which may cause flooding when the flooding is neither certain nor imminent. Flood watches may cover states, counties, rivers, portions of states, portions of counties, or portions of rivers (e.g., one or more forecast points). Flood Watches provide advance notice and up-to-date information on the possibility of flooding within 36 hours.

Flash Flood Warning

Flash flood warnings are issued when flooding is imminent. This product will be reserved for those short-term events which require immediate action to protect lives and property, such as dangerous small stream flooding or urban flooding, and dam or levee failures. Flash flood warnings may cover counties, portions of counties, well-known geographical areas (e.g., deserts, valleys), or river basins.

Flood Warning

Flood warnings are issued for any high flow, overflow, or inundation not covered by flash flood warning products. There are two general types of flood warnings - areal flood warnings and river flood warnings issued for specific forecast points. Flood warnings for forecast points usually include information on the impacts of expected flooding at locations upstream and/or downstream from covered forecast point(s) on a river or stream. Areal flood warnings are issued for areas along rivers and streams not associated with a forecast point, or for counties or portions of counties (with the areas covered described in the same way as for flash flood warnings).

Urban and/or Small Stream Advisories

Flood statements issued to provide information on elevated river/stream flows or ponding of water in urban or other areas, when such events warrant notification of the public in a product less urgent than a warning.

Lakeshore Flooding

The inundation of land areas along any of the Great Lakes over and above normal lake levels. This flooding may impact the immediate lakefront, bays, and interfaces between the Great Lakes and connecting waterways, such as rivers.

 

Lakeshore flooding intensities range from minor water overflow, with little or no damage, to significant water overflow, with extensive inundation and severe beach erosion. Lakeshore flooding is highly dependent on local coastline topography and nearshore bathymetry.

A "LAKESHORE FLOOD WATCH" informs the public lakeshore flooding is possible. A watch should be issued 12 to 36 hours in advance.

A "LAKESHORE FLOOD WARNING" informs the public lakeshore flooding, posing a serious threat to life and property, is occurring, imminent, or highly likely in the next 12 hours.