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How to access the latest weather forecast data from met.no
Navigating Thredds
Accessing files
Automatic fetching
NetCDF tools

How to access latest weather forecast data from met.no

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The weather forecast model output is available as NetCDF files on https://thredds.met.no/thredds/metno.html and the files follow the NetCDF/CF conventions. This page also documents how to navigate and access the data archived here. This page also documents how to access subsets of these files (to not have to download multiple GB of data)

Note also, that all communication to the thredds-server at Met requires a HTTPS connection, any HTTP-request reply with http error code 410: (410 Gone).

Navigating Thredds

When accesing the Weather Forecasts directory, the following screen greets you:

image.png

The 3 datasets covered in this documentation (MEPS, Arome Arctic and MET post-processed products) all have a latest and an archive folder. In the latest folder you find all the most recent forecasts and analysis. The archive folders are structured hierarchically by year, month and day of the month. image.png The content of the latest and archive catalogues per dataset are described here:

Accessing files

Following are some examples of how to access the files from the thredds-server using the OPeNDAP-protocol2, python or Fimex. There is also an option to download using a HTTPS-Server, though this is not adviced due to the file sizes involved.

Subsetting using OPeNDAP web access form

When clicking on a file in thredds, you get the following page:

image.png

If you click on the opendap link (in the red square), the OPeNDAP dataset access forms opens for that particular file. In this interface you can select the variables you want to download. In the example below we are only selected the x variable. In the field you can then fill out which subset of the variable you want to have in the format: start:step:end.

image.png

It updates the URL at in the Data URL field, which you can then use to access the subset of the data.

Subsetting using NetCDF libraries

Some python examples how to access the files are found in: Examples.

Subsetting using Fimex

The WMO has approved the GRIB-format for efficiently transmitting meteorological gridded data, so this is one of the preferred formats for exchanging data between meteorological services. GRIB has been around for some 35 years - since before the Internet and the PC was invented - with minimal changes to the format.

Being able to read GRIB data yourself, gives you the capacity to access gridded meteorological information from the weather services on the lowest possible level. This can be an advantage if you are looking for a reliable starting point for your data processing chain, which you plan to run with as little interruption as possible for the next decades to come.

Some basic receipts for installing and running the Fimex software for reading and interpolation GRIB2 files on Ubuntu are readily available here.

Automatic fetching

When setting up scripts for automatically fetch the latest available model output, we recommend parsing the catalogue.xml, not the html file. This will make it easy to discover when a new entry is added which can be accessed. Example: https://thredds.met.no/thredds/catalog/aromearcticlatest/latest/catalog.xml

NetCDF tools

Commonly used tools for viewing and manipulating NetCDF files.

  • Ncdump: Command line tool.

  • NCO: NCO contains a set of command-line tools to manipulate NetCDF files, such as: renaming or removing variables and dimensions; extracting subsets; averaging across dimensions; manipulating attributes.

  • Ncview: Ncview is used to view NetCDF files graphically.

  • Fimex: Fimex is a the File Interpolation, Manipulation and EXtraction library for gridded geospatial data.

  • Gridpp: Gridpp is the gridded post-processor. It includes methods for downscaling grids and bias-correcting fields.

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