Weather: differentiate forecast data

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (77e2890) 95.66% compared to head (208e460) 95.66%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #185 +/- ## ======================================= Coverage 95.66% 95.66% ======================================= Files 39 39 Lines 2538 2539 +1 Branches 478 478 ======================================= + Hits 2428 2429 +1 Misses 86 86 Partials 24 24 ``` | [Impacted Files](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer) | Coverage Δ | | |---|---|---| | [bemserver\_core/process/degree\_days.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvcHJvY2Vzcy9kZWdyZWVfZGF5cy5weQ==) | `100.00% <ø> (ø)` | | | [bemserver\_core/model/weather.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvbW9kZWwvd2VhdGhlci5weQ==) | `100.00% <100.00%> (ø)` | | | [bemserver\_core/process/weather.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvcHJvY2Vzcy93ZWF0aGVyLnB5) | `98.57% <100.00%> (ø)` | |

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