# Best Months by Climate Normals

> Typical weather per month from 1991–2020 normals, and the best months for an outdoor job. Finds the nearest weather station with official 1991–2020 climate normals — Deutscher Wetterdienst for Germany, NOAA for the United States — and rates every month for drying laundry, painting, mowing, barbecues or walks from its typical temperature and how often it rains.

Part of usefulweb.app (https://usefulweb.app/). Part of [Hearth](https://hearth.usefulweb.app/) (ownerApp: hearth). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://hearthclimatemonths.usefulweb.app/ (interactive tool at https://hearthclimatemonths.usefulweb.app/tool)
- JSON API: POST https://hearthclimatemonths.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://hearthclimatemonths.usefulweb.app/api/v1/tool)
- OpenAPI: https://hearthclimatemonths.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://hearthclimatemonths.usefulweb.app/mcp - tool `hearth_climate_months`

## Inputs
- place (text, required): Place (latitude, longitude) - Decimal degrees such as “52.52, 13.40”, or degrees-minutes-seconds. Rounded to 0.01° (about 1 km) before the request.
- activity (select): Activity

## Method
- Germany: the nearest of 1,090 Deutscher Wetterdienst climate stations (within 40 km) from the bundled 1991–2020 multi-annual means — monthly mean temperature, precipitation and sunshine; precipitation and sunshine come from the same station or the nearest one within 15 km.
- United States: the nearest NOAA NCEI station with 1991–2020 monthly normals, found with the NCEI search service in a box of ±0.4° (then ±1.2°) around the place; daily maximum and minimum temperature, precipitation and days with at least 0.10 inch of precipitation are converted to °C and mm. NCEI answers are cached for 30 days.
- Each month gets a temperature fit from the mean temperature (0 below the activity’s lower limit, 1 in its ideal band, falling to 0 six degrees above the upper limit) and a dryness: 1 − wet days / days in month (NOAA), or for DWD stations (no wet-day count) the relative sunshine duration n/N — the sunshine normal per day divided by the maximum possible sunshine at mid-month (FAO-56 eq. 34) — or, without a sunshine normal, 1 − precipitation / 150 mm. Score = 100 × fit × dryness.
- Bands (mean temperature, °C): drying 4–14 ideal to 30; painting 8–15 to 24; mowing 6–12 to 26; barbecue 10–18 to 27; walk −2–10 to 22. The best months are those within 10 points of the top score.

## Limits
- Normals describe the average of 30 years, not next year’s weather. Ratings are a planning heuristic; for the actual day use the forecast tools.