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amelie edited this page Sep 18, 2025 · 48 revisions

Updated: September 18, 2025: We are presently working on the final steps to publish MET Nordic Reanalysis version 4. This new version of the dataset focuses on improved precipitation. MET Nordic Reanalysis version 3 will not be accessible after 1/01/2026".

Updated: November 30, 2023: MET Nordic Reanalysis version 1 and 2 are no longer accessible. Please refer to MET Nordic Reanalysis Version 3.

Overview
Available data streams
Files
Parameters
Known data issues
Experimental probabilistic parameters
Experimental long-term consistent product
Derived products
References
More information

Overview

The MET Nordic dataset consists of post-processed products that (a) describe the current and past weather (analyses), and (b) give our best estimate of the weather in the future (forecasts). The products integrate output from MetCoOp Ensemble Prediction System (MEPS) as well as measurements from various observational sources, including crowdsourced weather stations. These products are deterministic, that is they contain only a single realization of the weather.

MET Nordic Analysis is the analysis product, which contains the weather for a given hour. MET Nordic Forecast is the most up-to-date forecast forward in time. The forecast length can vary from 58 to 64 hours, depending on how recent the available model input is. Both products are updated every hour as new observations and model fields become available. The dataset covers Norway, Denmark, Sweden, Finland, and part of the Baltic countries (see map on overview page). The grid has a spacing of 1 km. The coordinate reference system used is Lambert conformal conic and the proj4 string is "+proj=lcc +lat_0=63 +lon_0=15 +lat_1=63 +lat_2=63 +no_defs +R=6.371e+06".

The forecast product forms the basis for the forecasts on Yr (https://www.yr.no). Both analyses and forecasts are freely available for download.

Available data streams

The MET Nordic products are available in real-time and in our archive. The real-time stream contains the most recently produced (last 3 days) analyses and forecasts. Data in this folder is produced redundantly in two separate datahalls to ensure high availability.

Operationally produced data are archived, called the operational archive. Additionally, we occasionally rerun our system back in time in order to create an updated archive of historical analyses and forecasts, called the rerun archive. The methods used and their settings are consistent throughout such a rerun.

The latest rerun is Version 3. This was released in January 2023, and covers the time period 2012.09.01 - 2023.01.31. This archive can be combined with the operational archive to form a continuous time series from 2012.09.01 to the current time. For the time period where there is an overlap in operational and rerun archives, you should preferentially use the data from the latest rerun archive, since these will potentially have been produced using newer and better methods. The older rerun versions (1 and 2) are no longer accessible. We aim to release new reruns in the future when the methodology of the operational forecasts change significantly. Note that the current operational forecasts are not guaranteed to use the same methods as the latest rerun archive. We generally operationalize new improved methods as soon as they are ready, such that users of the operational forecasts (e.g. Yr) always receive the best forecasts we can make.

The various data streams are summarized as follows:

  • MET Nordic operational real-time:
    • Availability: last 3 days
    • Analyses and forecasts runs every hour
  • MET Nordic operational archive:
    • Availability: 2018.03.01 - now
    • Analyses available for every hour, forecasts available at 00Z, 06Z, 12Z, and 18Z.
  • MET Nordic rerun archive version 3:
    • Released January 2023.
    • Availability: 2012.09.01 - 2023.01.31
    • Includes analyses only
    • Changes relative to Version 2:
      • Fixed a bug in short-wave radiation
      • Added long-wave radiation
      • Changed algorithm for estimating precipitation
      • Improved cloud cover analyses and forecasts using webcameras
  • MET Nordic rerun archive version 2 (WARNING: This data stream is no longer accessible):
    • Released August 2020.
    • Changes relative to Version 1:
      • Improved Data quality control for precipitation. A larger number of observations have been used.
      • Fixed minor issues for the other variables.
      • Dataset delivers wind speed and direction, instead of x and y wind, which version 1 provides.
      • Extend the time period covered by the dataset up to December 2019.
  • MET Nordic rerun archive version 1 (WARNING: This data stream is no longer accessible):
    • released June 2019

The data availability can be visualized like this. Users wanting the best continuous timeseries should use the boxes filled with solid colours:

Data layout

Files

The files are available through https://thredds.met.no/thredds/metno.html under the folder called MET post-processed products. See the Data access page for information on how to download data.

The Latest folder contains the real-time stream of operational analyses and forecasts. The Archive/Operational folder contains the operational archive. The Archive/Rerun version 3 folder contains the most recent rerun of analyses and forecasts. Note that archive folders are only available in one of our datahalls. When that particular datahall is down for maintenance then the archive will temporarily not be available.

Links to the products are described in the table below. To download a file over HTTPS, prepend the filename with https://thredds.met.no/thredds/fileServer/. To access data with OpenDAP, prepend the path with https://thredds.met.no/thredds/dodsC/.

Stream Filenames
Operational real-time metpplatest/met_analysis_1_0km_nordic_{timestamp}.nc
metpplatest/met_forecast_1_0km_nordic_{timestamp}.nc
metpplatest/met_analysis_1_0km_nordic_latest.nc
metpplatest/met_forecast_1_0km_nordic_latest.nc
Operational archive metpparchive/{year}/{month}/{day}/met_analysis_1_0km_nordic_{timestamp}.nc
metpparchive/{year}/{month}/{day}/met_forecast_1_0km_nordic_{timestamp}.nc
Rerun archive version 3 metpparchivev3/{year}/{month}/{day}/met_analysis_1_0km_nordic_{timestamp}.nc
metpparchivev3/{year}/{month}/{day}/met_forecast_1_0km_nordic_{timestamp}.nc

where timestamp = {year}{month}{day}T{hour}Z (UTC or Zulu Time Zone), e.g. 20200601T12Z; Year is a 4-digit number (e.g. 2022); month is a 2-digit number (e.g. 02 for February); and day is a 2-digit number. Files ending in _latest.nc always point to the most recently produced files.

An example of a HTTPS URL is: https://thredds.met.no/thredds/fileServer/metpparchive/2020/06/01/met_analysis_1_0km_nordic_20200601T12Z.nc. An example OpenDAP URL is: https://thredds.met.no/thredds/dodsC/metpparchive/2020/06/01/met_analysis_1_0km_nordic_20200601T12Z.nc.

Parameters

Here are the variables that are available in the dataset. The starting point is the raw model output at 2.5 km resolution, which is then downscaled to 1km and then in some cases bias-corrected using observations.

NetCDF name Description Units
air_pressure_at_sea_level Instantaneous air pressure reduced to sea level. Bilinear interpolation from 2.5 km NWP. pa
air_temperature_2m Instantaneous temperature at 2 m. Downscaling from 2.5 km to 1 km using elevation gradient approach. Bias-correction using optimal interpolation observations from Netatmo, WMO-stations from MET and FMI, and other non-WMO stations in Norway. Forecast correction using a weighted average of recent temperature biases. K
cloud_area_fraction Fraction of sky covered by cloud. Bias corrected using webcameras from Luftambulansen. Correction to forecast 3 hours into the future. Bilinear interpolation from 2.5 km NWP. 1
integral_of_surface_downwelling_
shortwave_flux_in_air_wrt_time		 The time integral of incoming solar radiation at the surface over the hour leading up to the timestamp. The units are therefore W/m^2 s. Nearest neighbour interpolation from 2.5 km NWP. W/m^2 s
integral_of_surface_downwelling_
longwave_flux_in_air_wrt_time**		 The time integral of long wave radiation at the surface over the hour leading up to the timestamp. The units are therefore W/m^2 s. Nearest neighbour interpolation from 2.5 km NWP. W/m^2 s
precipitation_amount Precipitation accumulated over the hour leading up to the timestamp. Nearest neighbour downscaling. Bias-correction using observations from Netatmo, WMO-stations from MET and FMI, non-WMO stations in Norway, and radar. No forecast correction. mm
relative_humidity_2m Instantaneous relative humidity at 2 m. Bilinear interpolation from 2.5 km NWP. 1
wind_speed_10m 10 minute average speed of wind at 10m. Downscaling using an elevation gradient method. m/s
wind_direction_10m 10 minute average direction of wind at 10m. Direction is where wind is from, and 0 indicates wind from North (90 is from East). Downscaling using an elevation gradient method. Nearest neighbour interpolation from 2.5 km NWP. degree
altitude Altitude above sea-level of each grid cell m
land_area_fraction Fraction of each grid cell that is land (not sea) 1

(*) "integral_of_Y_wrt_X" means int Y dX. The data variable should have an axis for X specifying the limits of the integral as bounds. "wrt" means with respect to. The surface called "surface" means the lower boundary of the atmosphere. "shortwave" means shortwave radiation. Downwelling radiation is radiation from above. It does not mean "net downward". Surface downwelling shortwave is the sum of direct and diffuse solar radiation incident on the surface, and is sometimes called "global radiation". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.

(**) This variable has missing data for most of 2014, 2016, and 14 hours in 2019 (see Known data issues)

The reruns use whatever NWP modelling system was available at the time. The advantage of this rerun archive is that it offers a consistent set of filenames using a consistent domain, despite the fact that there a several different generations of the underlying model throughout the period. The history of the underlying NWP models used is:

Time period Modelling system
2020.02.04 - now MEPS (ensemble, 30 members)
2016.11.08 - 2020.02.03 MEPS (ensemble, 10 members)
2014.01.01 - 2016.11.07 MET AROME MetCoOp (deterministic)
2013.12.21 - 2013.12.31 MET AROME Norway (deterministic)
2012.09.01 - 2013.12.21 MET AROME MetCoOp reforecast (deterministic)

Known data issues

Here are a list of issues with the dataset that we are aware of:

  1. The background NWP model used changes significantly on 2016-11-08. Period to this, NWP modelling system contains a single determinsitic model run. After this date, the system consists of an ensemble of model runs. We have used different methods when assimilating observations into the MET Nordic dataset. Our view is that the dataset has higher quality after 2016-11-08.

  2. The background NWP model used for the analysis was not available for the time period 2019-03-03T13 to 2019-03-04T02. We have used forecast from the ECMWF model downscaled to 1.0 km to fill in this gap. Unfortunately, we do not have longwave radation for this period.

  3. Longwave radiation is not available in the reanalysis for the time period 2014-01-01T00Z to 2014-09-30T23Z, most of 2016, and 2019-03-03T13 to 2019-03-04T02.

Experimental probabilistic parameters

In addition to the above parameters, the files in Rerun archive version 3 also contain experimental parameters that aim to represent precipitation uncertainty. They are only available for the time period 2016.11.08-2023.01.31 since this is the time period for which an ensemble of NWP runs was available. The experimental parameters are:

NetCDF name Description Units
precipitation_amount_quantile 10th and 90th percentiles of the precipitation distribution. K
precipitation_amount_gt Probability of exceeding 0.1 mm of precipitation. 1

Experimental long-term consistent product

We have plans to post-process climate reanalysis datasets with similar methods as those used for MET Nordic analysis, such that additional data streams will be added to those presented above in Section Available data streams. Datasets based on reanalyses will allow for: i) reconstruction of longer time periods; ii) provide long-term consistent gridded fields of near-surface variables.

Currently, we have post-processed the NORA3 dataset (Haakenstad et al. 2021; Haakenstad and Breivik 2022) with statistical methods and the NORA3 near-surface fields are now available on the MET Nordic grid (1 km of grid spacing). The parameters considered are those described in the Table Parameters.

It is worth remarking that i) currently we have not combined NORA3 variables with observational data, though this is in our plan for the future; ii) this data stream is made available to the general public as an experimental product, which means that we have carried out a limited quality check of the data and that the dataset may change without warnings.

The data stream is summarized as follows:

  • MET Nordic long-term consistent:
    • Released June 2023.
    • Availability: 1975.01.01 - 2022.12.31 (updated with the latest data 3-4 times a year)
    • Includes analyses only
    • based on NORA3 hourly fields of near-surface variables

The dataset can be accessed as described in Section Files, at the path:

Stream Filenames
Long-term consistent version 1 metppltcarchivev1/{year}/{month}/{day}/met_analysis_ltc_1_0km_nordic_{timestamp}.nc

An example of a HTTPS URL is: https://thredds.met.no/thredds/fileServer/metppltcarchivev1/2020/06/01/met_analysis_ltc_1_0km_nordic_20200601T12Z.nc. An example OpenDAP URL is: https://thredds.met.no/thredds/dodsC/metppltcarchivev1/2020/06/01/met_analysis_ltc_1_0km_nordic_20200601T12Z.nc.

Derived products

We make available some products derived from the original MET Nordic analysis hourly gridded fields on the native grid of the original product. The derived products can be divided in two main classes: i) 3-hour or daily time-aggregated products; ii) climate indices.

These products are provided with limited support. The derived products for the data stream "Operational real-time" are updated on a daily/3-hourly basis. The other products will be updated periodically at our best convenience. You are welcome to use the products and report issues, but we reserve the right to respond and resolve reported problems with lower priority than for the other MET Nordic products.

Links to the products are similar to what described in Section Files. The specific indications for these files are shown in the following table:

Product Data Stream Filenames
Time aggregation Operational real-time force_derived_products/met_nordic_analysis/{year}/{month}/{day} met_analysis_1_0km_nordic_{variable}_{timeAgg}_{timestamp}.nc
Time aggregation Rerun archive version 3 force_derived_products/met_nordic_analysis/archive/rerun_version_3/daily_products/{year}/{month}/{day}/met_analysis_1_0km_nordic_{variable}_{timeAgg}_{timestamp}.nc
Climate indices Rerun archive version 3 force_derived_products/archive/rerun_version_3/climate_indices/{category}/{year}/ met_analysis_ltc_1_0km_nordic_{climateIndex}_{timeAggIndex}_{timestamp}.nc
Time aggregation Long-term consistent version 1 force_derived_products/met_nordic_analysis/long_term_consistent/version_1/daily_products/{year}/{month}/{day}/met_analysis_ltc_1_0km_nordic_{variable}_{timeAgg}_{timestamp}.nc
Climate indices Long-term consistent version 1 force_derived_products/long_term_consistent/version_1/climate_indices/{category}/{year}/ met_analysis_ltc_1_0km_nordic_{climateIndex}_{timeAggIndex}_{timestamp}.nc

where for time aggregation: variable = {tx (max temperature); tn (min temperature); tg (mean temperature); rr (precipitation total)}; timeAgg = { 24h (daily aggregation); 03h (3-hour aggregation)}; timestamp = end of the aggregation time period.

For climate indices: category = {precipitation; multi; heat; drought; cold} plus {average, reference}; climateIndex see the indices dictionary; timeAggIndex = {yr (yearly); hf (half-yearly); seas (season); mon (monthly)}; timestamp = end of the aggregation time period.

References

More information

You may find more information in the open issues or closed issues. If you want to contact us for something related to the dataset, we encourage you to open an issue. If you have any questions regarding the MET Nordic datasets please use this email address: metnordic[at]met.no

Copyright 2018-2024 Norwegian Meteorological Institute

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