Weather Observation Fetching

Overview

Retrieve measured surface and upper-air weather reports without losing station identity, observation time, units, raw values, or provider quality flags. Pick the source by observation type and retention need, then validate the returned records before normalization.

This skill covers METARs, historical surface observations, radiosondes, and station metadata. It excludes model output, radar volumes, and satellite imagery.

When to Use This Skill

• A task needs recent METAR observations for named stations or a small region.
• Historical hourly or synoptic surface data is needed from NOAA NCEI.
• A sounding workflow needs observed radiosonde profiles rather than model profiles.
• Station identifiers, relocations, instruments, or metadata must be resolved.
• A fetch returned duplicate, stale, unit-ambiguous, or quality-flagged values.

Do not use forecast products as observations, and do not substitute a nearby model grid point for a missing station report without explicit approval.

Choose the Source

Prefer an existing project adapter when it already handles the provider's schema, retries, and cache. Record the exact endpoint or archive object used.

Define the Observation Request

Resolve these values before fetching:

• observation type and variables;
• station identifier system, not just the identifier string;
• start and end instants in UTC, including interval inclusivity;
• maximum acceptable observation age;
• raw, decoded, or both output forms;
• required quality flags and policy for rejected values;
• output units and missing-value representation;
• cache location and retention.

For spatial queries, also define the search geometry, distance limit, and how a station is selected. Return the selected station and distance rather than silently using the nearest report.

Fetch Recent METARs

The Aviation Weather Center exposes machine-readable METAR data under /api/data/metar. Send a descriptive user agent, keep the query narrow, and handle a valid 204 No Content separately from an error.

import json
from urllib.error import HTTPError
from urllib.parse import urlencode
from urllib.request import Request, urlopen


def fetch_metars(stations, hours=2):
    station_ids = sorted({station.strip().upper() for station in stations})
    if not station_ids or any(len(station) != 4 for station in station_ids):
        raise ValueError("use one or more four-character ICAO station IDs")
    if not 1 <= hours <= 24:
        raise ValueError("hours must be between 1 and 24 for this narrow query")

    query = urlencode({
        "ids": ",".join(station_ids),
        "format": "json",
        "hours": hours,
    })
    request = Request(
        f"https://aviationweather.gov/api/data/metar?{query}",
        headers={"User-Agent": "weather-observation-fetching/1.0 contact@example.org"},
    )
    try:
        with urlopen(request, timeout=30) as response:
            if response.status == 204:
                return []
            records = json.load(response)
    except HTTPError as exc:
        if exc.code == 429:
            raise RuntimeError("AWC rate limit reached; honor Retry-After") from exc
        raise

    if not isinstance(records, list):
        raise RuntimeError("unexpected METAR response shape")
    return records

Replace the example contact address with an appropriate project contact. For a large current snapshot, download the provider's compressed cache file once instead of issuing many station queries.

Fetch Historical Surface Data

For ISD:

1. Resolve the station using the current station inventory and its USAF/WBAN identifiers.
2. Confirm that the station's coverage overlaps the requested time range.
3. Use bulk HTTPS files for a large historical request; avoid one network call per observation.

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