The author of this issue shared its template sensor for this: Problem pasing daily forecast · Issue #49 · jdejaegh/irm-kmi-ha · GitHub. There are other topics discussing this exact matter on this forum as it is common to all weather integrations (e.g. Update from using weather attributes with the new service: weather.get_forecasts)
Using the service weather.get_forecasts
(Weather - Home Assistant) will return the forecast for the next days (or hours). Using templates like the one share just above may help you getting it in an attribute if this is what you are looking for.