The National Weather Service (NWS) is the primary source for hydrologic watches, warnings, and advisories for the United States. Local NWS offices are responsible for issuing: Flood Watches, Flash Flood Watches, Flood Warnings, Flash Flood Warnings, and Flood Advisories. These products can and do emphasize different hydrologic issues depending on geographic area, land use, time of year, as well as other meteorological and non-meteorological factors. For example, during the early spring or late winter a Flood Warning can be issued for an ice jam that occurs on a river, while in the summer a Flood Warning will most likely be issued for excessive rainfall.
|Advanced Hydrologic Prediction Service|
Provides current levels of rivers located throughout the US and its territories.
|Hawaii · American Samoa · Guam · Puerto Rico/Virgin Islands|
In recent years, the NWS has enhanced its dissemination of hydrologic information through the Advanced Hydrologic Prediction Service (AHPS). AHPS allows anyone to view near real time observation and forecast data for rivers, lakes and streams. AHPS also enables the NWS to provide long-range probabilistic information which can be used for long-range planning decisions. Daily river forecasts are issued by the 13 River Forecast Centers (RFC) using hydrologic models based on rainfall, soil characteristics, precipitation forecasts, and several other variables. Some RFCs, especially those in mountainous regions, also provide seasonal snow pack and peak flow forecasts. These forecasts are used by a wide range of users, including those in agriculture, hydroelectric dam operation, and water supply resources. An AHPS guide for using their web site can be found here.
The WFO Juneau is responsible for the preparation and dissemination of all watches, warnings and advisories pertaining to flash flooding, river and stream flooding, and localized flooding in the Juneau Hydrologic Service Area (HSA). The Juneau HSA encompasses drainages over Southeast Alaska and the eastern Gulf Coast from Dixon Entrance to Cape Suckling. WFO Juneau is also responsible for reading the river gage located at the Mendenhall River in Juneau.
River Statement - Used to alert the public to changing river conditions in a non-warning or non-watch mode. For example, if there are a large number of logs or chunks of ice moving down a river this could be used to alert the public. This product could also be used to report very low water levels in a river which may restrict barge traffic.
Flood Advisory - Used when rainfall or snow melt causes water to pond on roadways, yards and/or small creeks and streams are near or at minor flood stage (nuisance flooding) but do not exceed moderate flood stage. This product can be used in both rural and urban areas, but the only designated urban area in Southeast Alaska is the Juneau zone.
Flood Watch and Flash Flood Watch - This is issued when flooding is possible, but not occurring at the present time.
Flood Warning - Issued when flooding is imminent or occurring. The criteria are based on established "moderate flooding" levels for specific rivers, but the warning is an areal forecast as impacts should play a role in the warning decision to threat of life and property.
Flood Statement - Used to update or cancel a flood warning or flood advisory.
Flash Flood Warning - Issued when a flash flood is imminent or occurring.
Flash Flood Statement - Issued to supplement information on an existing flash flood warning or to correct or cancel it.
Flash Flood Warning for Dam Break - This is what the name implies.
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