Flying Weather Index Data Sources

The Flying Weather Index is built entirely from public data. We publish derived statistics — not the raw third-party observations — and attribute every source below.

Last updated 2026-07-20 · Methodology version v1

Surface weather observations

Historical hourly and special surface observations come from the Iowa Environmental Mesonet (IEM) ASOS/AWOS archive, operated by Iowa State University, which archives and redistributes the underlying NOAA / National Weather Service observation record. These are the same METAR-format observations pilots read, spanning 2006–2025.

The IEM archive draws on NOAA's National Centers for Environmental Information (NCEI), including the Integrated Surface Database. We use the IEM distribution for consistent, station-by-station coverage; NCEI is the system of record for the underlying observations.

Current and recent conditions

Live METARs, TAFs, and flight categories elsewhere on ATIS Alerts come from aviationweather.gov (NOAA Aviation Weather Center). That feed powers current conditions only — it is not used for the long-term historical rankings.

Airport and runway data

Airport identifiers, locations, elevations, and runway headings come from the FAA-derived open airport dataset already used across ATIS Alerts (via OurAirports, which compiles FAA and other official sources). Runway true headings drive the crosswind analysis.

Time zone and daylight

Local time is derived from each airport's coordinates using IANA time-zone boundaries; sunrise and sunset are computed with a standard NOAA solar-position algorithm. These determine the “daylight” window used for daylight-VFR and estimated-VFR-day calculations.

Licensing and redistribution

The underlying NOAA/NWS observations are U.S. Government works in the public domain; the IEM archive is provided for public use with attribution. We redistribute only aggregated, derived statistics (percentages, medians, counts, and scores) — never bulk copies of the raw third-party observation files. Airport data is used under the terms of its open-data source. See the methodology for exactly how each statistic is computed.

Educational use only. Historical weather rankings from ATIS Alerts are educational summaries of past observations — not a forecast, flight-planning tool, or safety rating. They do not replace current METARs, TAFs, NOTAMs, ATIS, or a weather briefing, and favorable history does not make any airport safe. Always check current conditions and use your own judgment before flight.

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