Tools and Services
The NOAA National Operational Model Archive and Distribution System (NOMADS) provides information on available services for use with NOMADS data, along with a listing of some useful tools.
NOMADS Online Ensemble Probability Tool (EPT)
The NOMADS Ensemble Probability Tool allows you to query all 21 forecast ensemble members of the Global Ensemble Forecast System (GEFS) to determine the probability that a set of conditions will occur at a given location.
The EPT home page provides an easy-to-use interface to either select a location from a drop-down list or enter a latitude and longitude. Specific forecast variables or preset collections of variables for excessive heat, snow, blizzard conditions, fire weather, or thunderstorm potential can be selected. Output is returned as both text and an image displaying probabilities over the forecast period.
Introduction to Global Ensemble Forecast Probabilities
One of the most powerful improvements to Numerical Weather Prediction (NWP) in many years is ensemble forecasting. The NOMADS Ensemble Probability Tool allows users to interrogate the entire National Centers for Environmental Prediction (NCEP) Global Ensemble model suite with a single request. Ensemble models use slightly different initial (starting) conditions that reflect the fact that the current state of the atmosphere is not well known. There are only so many observations taken, and at great distances between them.
The complex nature of the atmosphere, coupled with inadequate observations and current computer models, results in forecasts that always contain uncertainties. NWS forecast products today are for the most part deterministic providing only one prediction of the future state of a system. Probabilistic forecasts convey uncertainty in the prediction (for example, a hurricane tracking cone of probabilities) but are usually not included in NWS forecasts and products today. Probabilistic forecasts, generated by ensemble models, convey uncertainty in the prediction.
The volume and complexities of ensemble datasets present an unparalleled access and use problem for even the most sophisticated end user. However, the NOMADS model archive and access system employing a distributed Service Orientated Architecture is well suited to provide easy to use temporal, variable, and geographic subsets of these data over the Internet.
For more information, please see the AMS paper on the subject: "A Client Application for Real Time NOMADS at NCEP to Disseminate NOAA's Information Data Base" by Alpert and Wang.
How to Use the Ensemble Probability Tool
- Select the geographic location you want to retrieve forecast information. This list is alphabetical and global. Typing in the first letter of the city in the pop-down list will scroll you to your selected city. Once selected, the latitude and longitude of that city is displayed on the page.
- Select the model run, or start time you want to use. The default is the most recent run of the models.
- Select the atmospheric variable or variables you wish to interrogate. To see if a city will experience a freezing event, select Temperature "less than" 0°C (or 32°F). Another example would be selecting "Precipitation" and select the amount of rainfall you are seeking a probability that will occur in millimeters of rainfall.
- Combinations of weather variables of temperature, precipitation, and wind force can be selected to see if such combined events will occur (temperature below 0°C AND winds in excess of 20 knots).
Note: In these cases, variables like precipitation are accumulated over 6-hourly intervals. The probabilities of events with precipitation are over 6-hourly periods so the amount of rain equivalent is over a 6-hour period. We didn't add up to get rainfall per day. The rest of the variables are snapshots.
The first bar in the graph represents the probability of the event at the time of the end of the first 6-hour forecast. Zero does not have a mark since precipitation amounts are only generated by the models for forecasts.
The results are displayed as percentages. For example, if 7 of the 14 ensembles met the parameters of your request, the probability is 50%. Finally, the results are for grid point locations on a longitude-latitude one-degree mesh. Note: For the Global Ensemble Forecast System (GEFS), which these are derived from, the resolution is 1 degree (approximately 111 km).
NOAA's Weather and Climate Toolkit allows you to download and visualize data available from NCEI, to include climate and weather data, radar data, satellite data, and NOMADS model data. The tool may be downloaded as stand-alone software or run through a java interface.
The tools listed below are freely available software that can be used with most NOMADS data. The list of tools is not all-inclusive. NCEI cannot guarantee the tools are free from viruses or could compromise the security of your computer system. The listing is not an endorsement for any particular organization and is provided for general informational purposes.
Wgrib is a command-line program useful for working with GRIB-1 files. It provides you with the ability to inventory, decode, and rewrite GRIB-1 files.
Wgrib2 is another command-line tool that works with both GRIB-1 and GRIB-2 files. It has much more functionality than Wgrib.
CDO tools are a set of command-line tools for both manipulating data files and for analyzing their data. Both GRIB and NetCDF file formats are supported with over 600 functions available for processing data.
NetCDF Operators is another set of command-line tools that perform several operations on NetCDF files. GRIB data downloaded from NOMADS can be converted to NetCDF format and used with NCO tools to perform a variety of operations on the data. NOMADS' services also provide conversion of GRIB data to NetCDF format.
Panoply is a Java application provided by NASA for plotting gridded data. It handles both GRIB and NetCDF file formats. Several types of plots can be made with Panoply: horizontal 2-D, vertical slices, time plots, and even 2-D arrays of values. Images can be saved and animations made. Various map projections and color scales can be chosen.
Ncview is a basic NetCDF file viewer. It was developed by David W. Pierce at the Scripps Institution of Oceanography, University of California, San Diego.
ncBrowse is a Java application provided by NOAA/PMEL/EPIC for plotting NetCDF files.
The Grid Analysis and Display System (GrADS) is available through the Institute of Global Environment and Society (IGES), Center for Ocean-Land-Atmosphere Studies (COLA). GrADS is an advanced tool for visualizing both gridded and station data from several different file formats, including GRIB, NetCDF, and BUFR. Several types of plots can be made with GrADS: contours, shaded contours, streamlines, barb plots, vector plots, line graphs, bar graphs, and station plots. GrADS may be used interactively or through pre-programmed scripts.
Ferret is a program useful for the analysis and visualization of gridded data. Designed for oceanographers and meteorologists, it is capable of utilizing OPeNDAP to retrieve data from NOMADS and other remote sites that provide OPeNDAP services.
The University Corporation for Atmospheric Research (UCAR) Computational & Information Systems Lab (CISL) program offers the National Center for Atmospheric Research (NCAR) Command Language (NCL). NCL is a program for analyzing and visualizing scientific data. NCL is an interpreted language suitable for making scripts. NCL handles many file formats, including GRIB and NetCDF.
The Integrated Data Viewer (IDV) is a Java-based set of libraries and applications for visualizing and analyzing various types of geophysical data. IDV was developed by the Unidata Program Center (UPC), University Corporation for Atmospheric Research (UCAR). IDV will render 3-D plots of data and allow you to interactively generate plots and animations.
The Man computer Interactive Data Access System (McIDAS) is another Java-based package of tools for analyzing and displaying geophysical data in two or three dimensions. Maintained by the Space Science and Engineering Center (SSEC) of the University of Wisconsin-Madison, McIDAS includes tools for handling various data types, including gridded GRIB and NetCDF data.
VAPOR is an advanced set of applications and libraries for visualizing gridded data. It enables you to render 3-D volumes, isosurfaces, contours, flow lines, and many other types of plots. Tools are included with VAPOR to convert GRIB, NetCDF, and other file formats into its own native VAPOR Data Collection (VDC) format.
Lawrence Livermore National Laboratory (LLNL) leads a consortium in the development of an open source collection of scientific data analysis and visualization utilities known as UV-CDAT. The utilities work with a variety of data types and are designed to work with the Earth System Grid Federation (ESGF).
The European Centre for Medium-Range Weather Forecasts (ECMWF) produces an application program interface (API) library for working with GRIB1 and GRIB2 files. The library can be used to develop software to encode, decode, and manipulate GRIB files. The library also comes with some command-line tools ready for compiling and using on GRIB files.
The University Corporation for Atmospheric Research (UCAR) Unidata program maintains a set of C, C++, and FORTRAN libraries for working with NetCDF files.
NOMADS Access Services
The following services are available for retrieving, viewing, and processing NOMADS data at NCEI.
THREDDS Data Server (TDS) is a web server available through NCEI NOMADS for a variety of methods to search, obtain information on, and download data. TDS provides services through OPeNDAP protocol, ncWMS, Web Coverage Services, ncISO, and NetCDF subset services. NOMADS datasets can be received through TDS by selecting TDS access links through the NOMADS data products pages or by navigating through the NOMADS' TDS catalog.
File Transfer Protocol (FTP)
File Transfer Protocol (FTP) is a standard network protocol provided by NCEI and NOMADS for downloading data files. NOMADS datasets can be received through the FTP service by selecting FTP access links through the NOMADS data products pages or by navigating through the NOMADS FTP directory structure.
Hypertext Transfer Protocol Secure (HTTPS)
HTTPS provides another standard network protocol to retrieve data files from NOMADS. HTTPS services are available by selecting HTTPS access links through the NOMADS data products pages or by navigating through the NOMADS' HTTPS directory structure.
The NCEI HDSS Access System (HAS) allows access to data stored on the Hierarchical Data Storage System (HDSS) tape robotics storage system. Model data not available online might be available offline though HAS by selecting HAS access links through the NOMADS data products pages or by navigating through the "Model" data section of the HAS System.
ERDDAP is another data server that gives you the means to subset gridded model data in several common file formats and to visualize data by making graphs and maps.