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This nowCOAST™ time-offsets map service provides maps of the latest nowcasts and forecast guidance of water temperature, water currents, and water level guidance from the NOS Lake Huron Operational Forecast System (LHOFS) at 6-hr increments out to 60 hours. Each forecast is valid for the specified forecast projection hour with respect to the latest forecast cycle time (e.g., 0, 6, 12 or 18 UTC). 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 LHOFS 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.
LHOFS is based on the Princeton Ocean Model (POM), a terrain following numerical ocean or hydrodynamic prediction model. The POM has been modified for use in the Great Lakes by NOAA/GLERL and The Ohio State University. The OFS grid domain covers Lake Huron. LHOFS is a 3-D forecast modeling system with a spatial horizontal resolution of 5 km and 20 terrain or sigma vertical levels. It has four forecast cycles per day (0000, 0600, 1200, and 1800 UTC) which generate forecast guidance out to 60 hours. The forecast cycle uses forecasts of surface wind velocity and surface air temperature from the NWS National Digital Forecast Database (NDFD). Each forecast cycle is preceded with a 1-hr long nowcast cycle. The latest nowcast serves as the initial conditions for each forecast cycle. The nowcoast cycle is driven by surface analyses of surface wind, air temperature, dew point temperature, and total cloud cover. LHOFS was developed and evaluate 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/glofs.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 nowCOAST™ map service is not time-enabled, although it does contain time-varying data. Instead of supporting the time dimension through use of a time parameter in each map request, each individual map layer contains data valid for a different "time offset", or forecast projection, from the dataset's reference time.
Due to software limitations, the full temporal resolution (i.e. maximum forecast horizon and/or all forecast projections) of the data is not provided by this service. Instead, a corresponding time-enabled service containing the full temporal resolution is available for this dataset, and users are highly encouraged to use that service instead, if possible.
This time-offsets map service is provided as a convenience for users who are not yet capable of interacting directly with the time dimension, especially users of legacy nowCOAST™ version 4 map services who wish to access the same data using the new nowCOAST™ version 5 map services. However, this service may be terminated with little advance notice at a later date.
In addition to ArcGIS Server REST access, time-enabled OGC WMS 1.3.0 access is is also provided by this service.
In order to determine the latest time information about the data included in this map service, users have two options: