ecmwf-opendata is a package to simplify the download of ECMWF open data. It implements a request-based interface to the dataset using ECMWF's MARS language to select meteorological fields, similar to the existing ecmwf-api-client Python package.

A collection of Jupyter Notebooks that make use of that package is available here.

The ecmwf-opendata Python package can be installed from PyPI with:

$ pip install ecmwf-opendata

The example below will download the latest available 10-day forecast for the mean sea level pressure (msl) into a local file called data.grib2:

from ecmwf.opendata import Client

client = Client()

client.retrieve(
    step=240,
    type="fc",
    param="msl",
    target="data.grib2",
)

❗ NOTE: This package is designed for users that want to download a subset of the whole dataset. If you plan to download a large percentage of each data file, it may be more efficient to download whole files and filter out the data you want locally. See the documentation on the file naming convention for more information. Alternatively, you can use this tool to download whole files by only specifying date, time, step, stream and type. Please be aware that all data for a full day is in the order of 726 GiB.

The constructor of the client object takes the following options:

client = Client(
    source="ecmwf",
    model="ifs",
    resol="0p25",
    preserve_request_order=False,
    infer_stream_keyword=True,
)

where:

• source is either the name of server to contact or a fully qualified URL. Possible values are ecmwf to access ECMWF's servers, or azure to access data hosted on Microsoft's Azure. Default is ecmwf.

• model is the name of the model that produced the data. Use ifs for the physics-driven model and aifs for the data-driven model. Please note that aifs is currently experimental and only produces a small subset of fields. Default is ifs.

• resol specifies the resolution of the data. Default is 0p25 for 0.25 degree resolution, and is the only resolution that is currently available.

• preserve_request_order. If this flag is set to True, the library will attempt to write the retrieved data into the target file in the order specified by the request. For example, if the request specifies param=[2t,msl] the library will ensure that the field 2t is first in the target file, while with param=[msl,2t], the field msl will be first. This also works across different keywords: ...,levelist=[500,100],param=[z,t],... will produce different output to ...,param=[z,t],levelist=[500,100],... If the flag is set to False, the library will sort the request to minimise the number of HTTP requests made to the server, leading to faster download speeds. Default is False.

• infer_stream_keyword. The stream keyword represents the ECMWF forecasting system that creates the data. Setting it properly requires knowledge of how ECMWF runs its operations. If this boolean is set to True, the library will try to infer the correct value for the stream keyword based on the rest of the request. Default is True if model is ifs.

⚠️ NOTE: It is recommended not to set the preserve_request_order flag to True when downloading a large number of fields as this will add extra load on the servers.

Client.retrieve()

The Client.retrieve() method takes request as input and will retrieve the corresponding data from the server and write them in the user's target file.

A request is a list of keyword/value pairs used to select the desired data. It is possible to specify a list of values for a given keyword.

The request can either be specified as a dictionary:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

request = {
    "time": 0,
    "type": "fc",
    "step": 24,
    "param": ["2t", "msl"],
}

client.retrieve(request, "data.grib2")

# or:

client.retrieve(
    request=request,
    target="data.grib2",
)

or directly as arguments to the retrieve() method:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    type="fc",
    step=24,
    param=["2t", "msl"],
    target="data.grib2",
)

The date and time keyword are used to select the date and time of the forecast run (see Date and time below). If date or both date and time are not specified, the library will query the server for the most recent matching data. The date and time of the downloaded forecast is returned by the retrieve() method.

from ecmwf.opendata import Client

client = Client(source="ecmwf")

result = client.retrieve(
    type="fc",
    step=24,
    param=["2t", "msl"],
    target="data.grib2",
)

print(result.datetime)

may print 2022-01-23 00:00:00.

Client.download()

The Client.download() method takes the same parameters as the Client.retrieve() method, but will download the whole data files from the server, ignoring keywords like param, levelist or number.

The example below will download all field from the latest time step 24, ignoring the keyword param:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.download(
    param="msl",
    type="fc",
    step=24,
    target="data.grib2",
)

Client.latest()

The Client.latest() method takes the same parameters as the Client.retrieve() method, and returns the date of the most recent matching forecast without downloading the data:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

print(client.latest(
    type="fc",
    step=24,
    param=["2t", "msl"],
    target="data.grib2",
))

may print 2022-01-23 00:00:00.

⏰ NOTE: The data is available between 7 and 9 hours after the forecast starting date and time, depending on the forecasting system and the time step specified.

The supported keywords are:

• type: the type of data (compulsory, defaults to fc).
• stream: the forecast system (optional if unambiguous, compulsory otherwise). See the infer_stream_keyword above.
• date: the date at which the forecast starts.
• time: the time at which the forecast starts.
• step: the forecast time step in hours, or fcmonth, the time step in months for the seasonal forecast (compulsory, default to 0 and 1, respectively).

and (all optional, with no defaults):

• param: the meteorological parameters, such as wind, pressure or humidity.
• levtype: select between single level parameters and parameters on pressure levels.
• levelist: the list of pressure levels when relevant.
• number: the list of ensemble member numbers when relevant.

The keywords in the first list are used to identify which file to access, while the second list is used to identify which parts of the files need to be actually downloaded. Some HTTP servers are able to return multiple parts of a file, while other can only return a single part from a file. In the latter case, the library may perform many HTTP requests to the server. If you wish to download whole files, only provide keywords from the first list.

The date and time parameters refer to the starting time of the forecast. All date and time are expressed in UTC.

There are several ways to specify the date and time in a request.

Date can be specified using strings, numbers and Python datetime.datetime or datetime.date objects:

...
    date='20220125',
    time=12,
...
    date='2022-01-25',
    time=12,
...
    date='2022-01-25 12:00:00',
...
    date=20220125,
    time=12,
...
    date=datetime.datetime(2022, 1, 25, 12, 0, 0),
...
    date=datetime.date(2022, 1, 25),
    time=12,
...

Dates can also be given as a number less than or equal to zero. In this case, it is equivalent to the current UTC date minus the given number of days:

...
    date=0, # today
    date=-1, # yesterday
    date=-2, # the day before yesterday
...

The keyword time can be given as a string or an integer, or a Python datetime.time object. All values of time below are equivalent:

...
    time=12,
...
    time=1200,
...
    time='12',
...
    time='1200',
...
    time=datetime.time(12),
...

If time is not specified, the time is extracted from the date.

...
   date='2022-01-25 12:00:00',
...

is equivalent to:

...
   date='2022-01-25',
   time=12,
...

If the time keyword is specified, it overrides any time given in the request.

...
   date='2022-01-25 12:00:00',
   time=18,
...

is equivalent to:

...
   date='2022-01-25',
   time=18,
...

As stated before, if date or both date and time are not specified, the library will query the server for the most recent matching data. The date and time of the downloaded forecast is returned by the retrieve() method:

Example without the date keyword:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

result = client.retrieve(
    time=12,
    type="fc",
    param="2t",
    step="24",
    target="data.grib2",
)

print(result.datetime)

will print 2022-01-22 12:00:00 if run in the morning of 2022-01-23.

Example without the date and time keywords:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

result = client.retrieve(
    type="fc",
    param="2t",
    step="24",
    target="data.grib2",
)

print(result.datetime)

will print 2022-01-23 00:00:00 if run in the morning of 2022-01-23.

ECMWF runs several forecasting systems:

• HRES: High Resolution Forecast.
• ENS: Ensemble Forecasts.
• SEAS: Long-Range (Seasonal) Forecast.

Each of these forecasts also produces several types of products, that are referred to using the keywords stream and type.

Valid values for type are:

HRES:

• fc: Forecast.

ENS:

• cf: Control forecast.
• pf: Perturbed forecast.
• em: Ensemble mean.
• es: Ensemble standard deviation.
• ep: Probabilities.

Valid values for stream are:

• oper: Atmospheric fields from HRES - 00 UTC and 12 UTC.
• wave: Ocean wave fields from HRES - 00 UTC and 12 UTC.
• enfo: Atmospheric fields from ENS.
• waef: Ocean wave fields from ENS.
• scda: Atmospheric fields from HRES - 06 UTC and 18 UTC.
• scwv: Ocean wave fields from HRES - 06 UTC and 18 UTC.

📌 NOTE: if the client's flag infer_stream_keyword is set to True, the library will infer the stream from the type and time. In that case, you just need to specify stream=wave to access ocean wave products, and don't provide a value for stream in other cases.

To select a time step, use the step keyword:

...
   step=24,
...
   step=[24, 48],
...

📌 NOTE: Not specifying step will return all available time steps.

To select a parameter, use the param keyword:

...
   param="msl",
...
   param=["2t", "msl"]
...

for pressure level parameters, use the levelist keyword:

...
   param="t",
   levelist=850,
...
   param=["u", "v"],
   levelist=[1000, 850, 500],
...

📌 NOTE: Not specifying levelist will return all available levels, and not specifying param will return all available parameters.

Below is the list of all parameters:

Atmospheric fields on pressure levels

Atmospheric fields on a single level

Ocean waves fields

Ensemble mean and standard deviation - pressure levels

Ensemble mean and standard deviation - single level

Instantaneous weather events - atmospheric fields - 850 hPa

Daily weather events - atmospheric fields - single level

Instantaneous weather events - ocean waves fields

You can select individual members of the ensemble forecast use the keyword number.

...
   stream="enfo",
   step=24,
   param="msl",
   number=1,
...
   stream="enfo",
   step=24,
   param="msl",
   number=[1, 10, 20],
...

📌 NOTE: Not specifying number will return all ensemble forecast members.

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="oper",
    type="fc",
    step=24,
    param="2t",
    target="data.grib2",
)

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="oper",
    type="tf",
    step=240,
    target="data.bufr",
)

• The downloaded data are encoded in BUFR edition 4
• For the HRES Tropical Cyclone tracks at time=06 and time=18 use:

...
   step = 90,
...

❗ NOTE: Tropical cyclone tracks products are only available when there are tropical cyclones observed or forecast.

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="enfo",
    type="pf",
    param="msl",
    target="data.grib2",
)

• To download a single ensemble member, use the number keyword: number=1.
• All of the odd numbered ensemble members use number=[num for num in range(1,51,2)].
• To download the control member, use type="cf".

The Tropical Cyclone tracks are identified by the keyword type="tf".

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="enfo",
    type="tf",
    step=240,
    target="data.bufr",
)

• The downloaded data are encoded in BUFR edition 4
• For the ENS Tropical Cyclone tracks at time=06 and time=18 replace step=240 with step=144.

The ensemble mean and standard deviation are identified by the keywords type="em":

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="enfo",
    type="em",
    step=24,
    target="data.grib2",
)

and type="es", respectively:

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="enfo",
    type="es",
    step=24,
    target="data.grib2",
)

The ensemble probability products are identified by the keyword type="ep". The probability products are available only for time=00 and time=12.

Two different products are available.

The probability of temperature standardized anomalies at a constant pressure level of 850hPa are available at 12 hourly forecast steps.

from ecmwf.opendata import Client

client = Client(source="ecmwf")

client.retrieve(
    time=0,
    stream="enfo",
    type="ep",
    step=[i for i in range(12, 361, 12)],
    levelist=850,
    param=[
        "ptsa_gt_1stdev",
        "ptsa_gt_1p5stdev",
        "ptsa_gt_2stdev",
        "ptsa_lt_1stdev",
        "ptsa_lt_1p5stdev",
        "ptsa_lt_2stdev",
    ],
    target="data.grib2",
)

The probabilities of total precipitation and wind gusts exceeding specified thresholds in a 24 hour period are available for step ranges 0-24 to 336-360 by 12​​. These are specified in the retrieval request using, e.g.: step=["0-24", "12-36", "24-48"].

from ecmwf.opendata import Client

client = Client(source="ecmwf")

steps = [f"{12 * i}-{ 12 * i + 24}" for i in range(29)]

client.retrieve(
    time=0,
    stream="enfo",
    type="ep",
    step=steps,
    param=["tpg1", "tpg5", "10fgg10"],
    target="data.grib2",
)

By downloading data from the ECMWF open data dataset, you agree to the their terms: Attribution 4.0 International (CC BY 4.0). If you do not agree with such terms, do not download the data. Visit this page for more information.

Apache License 2.0 In applying this licence, ECMWF does not waive the privileges and immunities granted to it by virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.