Valid date range to retrieve IFS forecasts from ECMWF open-data

Datasets and Usage
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1

Hi,

I’m using the ECMWF OpenData Python package to retrieve IFS forecasts. When I try various dates with client.retrieve(), I repeatedly get the following error:

requests.exceptions.HTTPError: 404 Client Error: Not Found for url: ``https://data.ecmwf.int/forecasts/20250901/00z/ifs/0p25/oper/20250901000000-6h-oper-fc.index

The only dates that have worked are after 2025-09-30. Is this because the OpenData package has a limited date range for IFS forecasts? If so, what would be the recommended way to access past IFS forecasts?

I’ve put my Python script below for reference. I’d greatly appreciate any guidance, as I’m a high school researcher working under a tight deadline over the next few days.

Thank you in advance for your time and help!

from ecmwf.opendata import Client

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

client.retrieve(
    date="2025-09-01",
    time=0,
    type="fc",
    step=6,
    param=["msl"],
    target="ifs_test.grib2"
)
2

Hi Cynthia,

We only keep 4 days archive on the open data server.

Amazon Web Services keep longer archive, so if you replace source=“ecmwf”, will h source=“aws”, you should be able to get older dates.

Full forecast archive is available in our MARS archive, but that is subject to a fee.

I hope this helps.

Milana