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This nowCOAST™ time-enabled 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 hourly 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 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 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: