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This nowCOAST™ time-offsets map service provides maps depicting the NWS 6-hr quantitative precipitation [amount] forecasts (QPF) from the National Digital Forecast Database (NDFD) ending at specified forecast projection hours out to 2-3 days (NDFD has forecasts out to 7 days which are available via the nowCOAST™ time-enabled map service for NDFD elements). The 6-hr QPF describes the amount of precipitation (rainfall, melted snow and/or sleet) occurring at a location within the specified 6-hour time period. The forecasts 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.
The precipitation amount is indicated by different colors at 0.01, 0.10, 0.25 inches and then at 1/4 inch intervals up to 4.0 inches (e.g. 0.50, 0.75, 1.00, 1.25, etc.), at 1-inch intervals from 4 to 10 inches and then at 2-inch intervals up to 14+ inches. The increments from 0.01 to 1.00 or 2.00 inches are similar to what are used on NCEP's Weather Prediction Center QPF products and the NWS River Forecast Center (RFC) daily precipitation analysis.
The 6-hr quantitative precipitation forecast (QPF) describes the amount of precipitation (rainfall, melted snow and/or sleet) occurring at a location within a specified 6-hour time period.
The NDFD is a seamless composite or mosaic of gridded forecasts from individual NWS Weather Forecast Offices (WFOs) from around the U.S. as well as the NCEP Ocean Prediction Center and National Hurricane Center/TAFB for certain marine weather variables. NDFD has a spatial resolution of 2.5 km (1.6 miles). The time resolution of forecast projections varies by variable (element) based on user needs, forecast skill, and forecaster workload. Each WFO prepares gridded NDFD forecasts for their specific geographic area of responsibility. When these locally generated forecasts are merged into a national mosaic, occasionally areas of discontinuity will be evident. Staff at NWS forecast offices attempt to resolve discontinuities along the boundaries of the forecasts by coordinating with forecasters at surrounding WFOs and using workstation forecast tools that identify and resolve some of these differences. The NWS is making progress in this area, and recognizes that this is a significant issue in which improvements are still needed. The NDFD was developed by NWS Meteorological Development Laboratory.
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: