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nowcoast/analysis_meteohydro_sfc_rtma_time (MapServer)

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Service Description:
Last Revised: February 2016

Map Information

This nowCOAST™ time-enabled map service provides maps depicting the past four hours of surface meteorological analyses of air temperature, dew point temperature, visibility, wind velocity, wind speed, wind gust, and 1-hr accumulated precipitation from the NWS/NCEP Real-Time Mesoscale Analysis (RTMA) system. The horizontal spatial resolution depends on geographic region: 2.5 km (1.6 miles) horizontal resolution for CONUS, Hawaii, Puerto Rico and Guam and 3 km (1.86 miles) for Alaska region.

The air and dew point temperatures are indicated on the map by different colors at 2 degree Fahrenheit increments from -30 to 130 degrees F in order to use same color legend throughout the year for the United States. The same color scale is used for displaying the NDFD maximum and minimum air temperature forecasts.

The visibility is indicated on the map by different colors for the following ranges: 0 - 0.24, 0.25 - 0.49, 0.5 - 0.74, 0.75 - 0.99, 1.0 - 2.9, 3.0 - 4.9, 5.0 - 6.9, and 7.0+ miles, in order to correspond with thresholds important to mariners and aviators as well as thresholds associated with visibility-related watches, warnings and advisories issued by the National Weather Service.

The total precipitation amount is indicated by different colors at 0.01, 0.10, 0.25 and then at 1/4 inch intervals up to 4.0 (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 the NCEP Weather Prediction Center QPF products and the NWS River Forecast Center (RFC) daily precipitation analysis.

Wind speed and wind gust are indicated on the map by different colors for 5 knot increments up to 115 knots. The legend includes tick marks for both knots and miles per hour. The same color scale is used for displaying the NDFD wind speed/gust forecasts. The wind velocity is depicted by curved wind barbs along streamlines. The direction of the wind barb is indicated with an arrowhead. The flags on the wind barb are the standard meteorological convention in units of knots.

The analyses are updated in the nowCOAST™ map service every hour. For more detailed information about layer update frequency and timing, please reference the nowCOAST™ Dataset Update Schedule.

Background Information

The NCEP RTMA system is an hourly, high-resolution, objective analysis/assimilation system for near-real surface weather conditions. RTMA uses the Two-Dimensional Variational Analysis mode of NCEP's Gridpoint Statistical Interpolation (GSI). The first guess for the RTMA analyses for Alaska, Puerto Rico, Guam, and HI domains are provided by downscaled forecasts from NCEP's North American Mesoscale (NAM) Model. The first guess for OCONUS domain analyses are from the 1-hour forecasts of the NCEP Rapid Refresh system. The RTMA system was developed by NCEP/Environmental Modeling Center/Mesoscale Modeling Branch in cooperation with NOAA/Office of Oceanic and Atmospheric Research/Environmental Research Laboratory.

Time Information

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:

  1. Issue a returnUpdates=true request (ArcGIS REST protocol only) for an individual layer or for the service itself, which will return the current start and end times of available data, in epoch time format (milliseconds since 00:00 January 1, 1970). To see an example, click on the "Return Updates" link at the bottom of the REST Service page under "Supported Operations". Refer to the ArcGIS REST API Map Service Documentation for more information.
  2. Issue an Identify (ArcGIS REST) or GetFeatureInfo (WMS) request against the proper layer corresponding with the target dataset. For raster data, this would be the "Image Footprints with Time Attributes" layer in the same group as the target "Image" layer being displayed. For vector (point, line, or polygon) data, the target layer can be queried directly. In either case, the attributes returned for the matching raster(s) or vector feature(s) will include the following:
    • validtime: Valid timestamp.
    • starttime: Display start time.
    • endtime: Display end time.
    • reftime: Reference time (sometimes referred to as issuance time, cycle time, or initialization time).
    • projmins: Number of minutes from reference time to valid time.
    • desigreftime: Designated reference time; used as a common reference time for all items when individual reference times do not match.
    • desigprojmins: Number of minutes from designated reference time to valid time.
  3. Query the nowCOAST™ LayerInfo web service, which has been created to provide additional information about each data layer in a service, including a list of all available "time stops" (i.e. "valid times"), individual timestamps, or the valid time of a layer's latest available data (i.e. "Product Time"). For more information about the LayerInfo web service, including examples of various types of requests, refer to the nowCOAST™ LayerInfo Help Documentation


Map Name: NOAA NWS NCEP Real-Time Mesoscale Analysis (RTMA) (Time Enabled)


All Layers and Tables

Dynamic Legend

Dynamic All Layers

Layers: Description:


Spatial Reference: 102100  (3857)

Single Fused Map Cache: false

Initial Extent: Full Extent: Time Info: Units: esriMeters


Document Info: Supports Dynamic Layers: true

MaxRecordCount: 1000

MaxImageHeight: 4096

MaxImageWidth: 4096

Supported Query Formats: JSON, AMF, geoJSON

Min Scale: 0

Max Scale: 0

Supports Datum Transformation: true

Child Resources:   Info   Dynamic Layer

Supported Operations:   Export Map   Identify   Find   Return Updates