# Fog Atlas

> Fog climatology and verified fog forecasts for 3497 airports worldwide,
> built for EFVS flight operations and anyone asking "will it be foggy tomorrow?".
> Climatology: hourly METAR observations 2016-01-01 to 2026-08-15
> (Iowa Environmental Mesonet). Forecasts: NOAA/NWS National Blend of Models,
> recalibrated per airport and verified against live observations. Forecast
> percentages are published ONLY for airports whose calibrated model beat that
> airport's own climatology on live verification (235 airports currently);
> all issued forecasts are logged and scored — receipts at /fog/scorecard/.

Updated 2026-10-07. Pages rebuild daily; the forecast API updates hourly.
License: CC BY 4.0 — reuse freely, attribution = a link to the airport or city page you used. Not for operational use.

## Per-airport pages (start here)
- [Airport index](https://fogatlas.org/fog/): every airport, linked; pattern https://fogatlas.org/fog/{icao_lowercase}/ (e.g. https://fogatlas.org/fog/ksfo/). The first block is today's answer in plain language; a facts box carries the climatology and approach-capability numbers
- [Airport machine index](https://fogatlas.org/fog/index.json): one row per airport — icao, iata, name, city, country, lat/lon, tz, fog hours/yr, peak months, forecast status, page and data.json URLs
- [Example airport data](https://fogatlas.org/fog/ksfo/data.json): the per-airport JSON contract (schemaVersion, identity, climatology incl. monthly hours and causes, approach capability, today's baked answer with threshold definition, latest observation, verification receipt, nearby airports, validThrough)
- Three attributed forecast sources on US pages: NWS model guidance (the National Blend of Models — "forecast.guidanceSource" — which is what the calibration uses; "dense-fog signal" there means visibility under a mile), the airport's own terminal forecast (TAF, "forecast.taf"), and the NWS public point forecast from api.weather.gov quoted verbatim and attributed to the issuing office ("forecast.nws": office, issued, verdict, mentions[].phrase/period). A fog mention in "forecast.nws" is NWS wording — "patchy fog", "areas of fog", "widespread fog", "dense fog" — not a Fog Atlas probability, and the site never converts it into one; mentions[].period is the NWS period name verbatim and mentions[].periodLabel resolves a relative one ("Tonight") to the day it meant. Non-US pages carry the TAF and, where covered, the model guidance

## City pages
- [City index](https://fogatlas.org/fog/city/): every city with a measuring station; pattern https://fogatlas.org/fog/city/{slug}/ — US/CA/AU slugs carry a region suffix (https://fogatlas.org/fog/city/san-francisco-ca/); each page names its measuring stations and takes its answer from the city's primary station
- [City machine index](https://fogatlas.org/fog/city/index.json): slug, city, region, country, stations, primary station, page and data.json URLs
- [Example city data](https://fogatlas.org/fog/city/san-francisco-ca/data.json)

## Where it will be foggy tomorrow
- [Fog forecast — where fog is expected in the next 36 hours](https://fogatlas.org/fog/forecast/): rebuilt daily; airports with a verified calibrated probability of 50% or more, airports whose own terminal forecast (TAF) calls for dense fog, US airports whose NWS public point forecast mentions fog (quoted verbatim, "nwsForecastFog" in data.json), and airports reporting fog at the latest observation, worldwide

## Regions, rankings and capability lists
- [Tule fog — California Central Valley](https://fogatlas.org/fog/region/central-valley/) and [North India winter fog](https://fogatlas.org/fog/region/north-india/): season, member airports, aggregated monthly hours
- [Foggiest airports in the world](https://fogatlas.org/fog/foggiest-airports/) and [foggiest US airports](https://fogatlas.org/fog/foggiest-us-airports/): ranked by hours/yr below CAT I minima, quality-gated
- [CAT III airports](https://fogatlas.org/fog/cat-iii-airports/), [CAT II airports](https://fogatlas.org/fog/cat-ii-airports/), [EFVS credit explained](https://fogatlas.org/fog/efvs/)

## Live APIs (JSON)
- [Forecast issuance](https://fogatlas.org/api/forecast): hourly calibrated issuance for all covered airports — meta.cycle, meta.publicAirports (the verified list), per-airport fhrs + p rows [P(vis<1mi), P(<0.5), P(<0.25), P(below CAT I)] in percent; calibrated values for airports NOT in meta.publicAirports are unverified and must not be quoted as Fog Atlas forecasts
- [Latest observations](https://fogatlas.org/api/metar?ids=KSFO): NOAA AWC passthrough, ids=ICAO[,ICAO]
- [Verification scorecard](https://fogatlas.org/api/scorecard): Brier skill vs climatology, pooled and per airport

## Optional
- [Verification & the publication bar](https://fogatlas.org/fog/scorecard/)
- [Methodology](https://fogatlas.org/methodology/): band definitions, sources, honesty ledger
- [About](https://fogatlas.org/about/)
- [Hourly climatology detail](https://fogatlas.org/data/detail/KSFO.json): 12x24 month-by-hour grids per airport
- [Sitemap index](https://fogatlas.org/sitemap.xml): priority, airports, cities