Fog Atlas
A worldwide map of where the sky closes — ten years of METAR observations distilled into when, where, and how often airports drop below approach minima, and how much of that an EFVS-equipped aircraft gets back.
Enhanced Flight Vision Systems (EFVS) let suitably equipped aircraft fly approaches in visibility that would otherwise force a diversion. The value of that equipment is concentrated at a specific kind of airport: one that is frequently fogbound and lacks CAT II/III ILS infrastructure. Fog Atlas maps that intersection from public data.
What it shows
Every METAR observation is classified into one of three visibility bands:
| Band | Prevailing visibility | Meaning |
|---|---|---|
| Normal ops | ≥ 800 m (½ SM) | Conventional CAT I approach workable |
| EFVS-recoverable | 300–800 m | Below typical CAT I minima, but within EFVS-usable range |
| Below all | < 300 m | Too low for EFVS too; CAT III autoland territory |
Aggregated by airport × month × hour-of-day over a 10-year archive, tagged by cause (fog, mist, haze, smoke, snow), and cross-referenced with CAT II/III capability.
Data sources
- METAR archive: Iowa Environmental Mesonet (IEM) ASOS/METAR archive, backfilled from NOAA ISD for stations IEM covers thinly.
- Airports: OurAirports open data.
- CAT II/III capability: FAA CIFP for US airports; hand-curated list for international (see methodology for confidence levels).
- Cancellations (US validation layer): US DOT Bureau of Transportation Statistics on-time performance data.
Honest limitations
METAR prevailing visibility is a proxy for RVR, not a substitute. Band thresholds are global approximations, not per-runway minima. International station data quality varies. CAT II/III flags outside the US are curated, not authoritative. Full methodology and assumptions: METHODOLOGY.md.
Layout
pipeline/— Python + DuckDB ingestion and aggregation (offline; produces static JSON)app/— static web app (Vite + MapLibre GL + Observable Plot)
Live
https://fog-atlas.pages.dev — 3,394 airports × 10 years (2016–2025), visibility + ceiling bands, a live fog-chase board for EFVS testing (per-runway ALS/RVR/minima filters from FAA NASR, still-air ETE from a chosen base, 3-minute live strata + nowcast), validated against documented climatology, runway-measured RVR (SFO cross-check), and 13.9M US flight records (flights scheduled during EFVS-recoverable hours were weather-cancelled at 5.2× baseline).
Who makes this
Fog Atlas is built and run by Travis Danner as an open, public-data reference — the pipeline and methodology are on GitHub. Every forecast the site issues is logged and publicly scored on the verification page. Not for operational use.
Live world fog map · all airports · by city · forecast verification · methodology · about · llms.txt. Not for operational use.