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This nowCOAST™ time-enabled map displays the latest nowcasts and forecast guidance of water temperature, water currents, and water level guidance from the NOS Lake Erie Operational Forecast System (LEOFS) at 3-hr increments out to 60 hours. The direction of the water currents are depicted by white streaklets. The magnitude of the current is indicated by the length and width of the streaklet as well as by the color-coded speed background. The water levels are referenced to Low Water Datum of IGLD85. The maps of LEOFS forecast guidance are updated in the nowCOAST™ map service four times per day. For more detailed information about layer update frequency and timing, please reference the nowCOAST™ Dataset Update Schedule.
LEOFS is a 3-D lake forecast modeling system providing updated nowcasts and short-range forecasts guidance of water temperatures, currents, and water levels for Lake Erie. LEOFS is based on the Finite Volume Community Ocean Model (FVCOM), a numerical ocean circulation or hydrodynamic prediction model. The model has a horizontal resolution ranging from approximately 3.5 km offshore to 400 m near the shore and has 20 terrain-following or sigma levels. LEOFS has four forecast cycles per day (0000, 0600, 1200, and 1800 UTC) which generate forecast guidance out to 120 hours, however nowCOAST presently only displays the output out to 60 hours. The forecast cycle uses meteorological forecasts from the NWS National Digital Forecast Database (NDFD) which has a horizontal resolution of 2.5 km. Each forecast cycle is preceded with a nowcast cycle, which uses the 2-hr forecast guidance from the NWS High Resolution Rapid Refresh (HRRR) numerical weather prediction system. The HRRR system has a horizontal resolution of 3 km. Lateral boundary conditions for water levels are provided by near-real-time water level observations from NOS gages at Gibralter, MI (near Detroit River) and Buffalo, NY (near the Niagara River). An offset for each open boundary is applied to the observed water level to account for the river channel representation and/or distance between gage and boundary location on the grid. The lateral boundary conditions for water temperatures are provided by a USGS ADCP located in the Detroit River near Fort Wayne, MI. The boundary conditions for the forecast cycle are persisted from the nowcast cycle. The latest nowcast serves as the initial conditions for each forecast cycle. LEOFS was developed and evaluated by NOAA/GLERL and the NOAA/NOS/CSDL Coastal Marine Modeling Branch. It was implemented operationally on the NOAA Weather and Climate Operational Supercomputer System (WCOSS) by the NOS Center for Operational Oceanographic Products and Services (CO-OPS) in collaboration with NWS/NCEP Central Operations. For more information, please see http://tidesandcurrents.noaa.gov/ofs/leofs/leofs.html.
The maps are generated using a visualization technique developed by the Data Visualization Research Lab at The University of New Hampshire's Center for Coastal and Ocean Mapping (http://www.ccom.unh.edu/vislab/). The method combines two techniques. First, equally spaced streamlines are computed in the flow field using Jobard and Lefer's (1977) algorithm. Second, a series of "streaklets" are rendered head to tail along each streamline to show the direction of flow. Each of these varies along its length in size, color and transparency using a method developed by Fowler and Ware (1989), and later refined by Mr. Pete Mitchell and Dr. Colin Ware (Mitchell, 2007).
This map service is time-enabled, meaning that each individual layer contains time-varying data and can be utilized by clients capable of making map requests that include a time component.
In addition to ArcGIS Server REST access, time-enabled OGC WMS 1.3.0 access is also provided by this service.
This particular service can be queried with or without the use of a time component. If the time parameter is specified in a request, the data or imagery most relevant to the provided time value, if any, will be returned. If the time parameter is not specified in a request, the latest data or imagery valid for the present system time will be returned to the client. If the time parameter is not specified and no data or imagery is available for the present time, no data will be returned.
This service is configured with time coverage support, meaning that the service will always return the most relevant available data, if any, to the specified time value. For example, if the service contains data valid today at 12:00 and 12:10 UTC, but a map request specifies a time value of today at 12:07 UTC, the data valid at 12:10 UTC will be returned to the user. This behavior allows more flexibility for users, especially when displaying multiple time-enabled layers together despite slight differences in temporal resolution or update frequency.
When interacting with this time-enabled service, only a single instantaneous time value should be specified in each request. If instead a time range is specified in a request (i.e. separate start time and end time values are given), the data returned may be different than what was intended.
Care must be taken to ensure the time value specified in each request falls within the current time coverage of the service. Because this service is frequently updated as new data becomes available, the user must periodically determine the service's time extent. However, due to software limitations, the time extent of the service and map layers as advertised by ArcGIS Server does not always provide the most up-to-date start and end times of available data. Instead, users have three options for determining the latest time extent of the service: