@Cyanheads/Aviation Weather Server

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Overview

Aviation weather from the NWS Aviation Weather Center — METARs, TAFs, PIREPs, and domestic SIGMETs. Look up stations, fetch current and forecast conditions, and pull pilot reports and hazard advisories from any MCP client. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.

Tools

Tool	Description
aviation_find_stations	Resolve airports and weather stations by identifier, bounding box, or US state. Returns ICAO/IATA/FAA IDs, coordinates, elevation, and available data types.
aviation_get_metar	Get current weather observations (METARs) for one or more airports. Returns decoded wind, visibility, ceiling, present weather, temp/dewpoint, altimeter, cloud layers, flight category (VFR/MVFR/IFR/LIFR), and the raw METAR string.
aviation_get_taf	Get Terminal Aerodrome Forecasts for one or more airports. Returns each forecast period with valid times, surface wind, low-level wind shear, visibility, decoded weather, cloud layers, and vertical visibility into a forecast obscuration, plus the raw TAF string.
aviation_get_pireps	Get recent Pilot Reports near an airport or within a bounding box. Returns decoded turbulence, icing, and cloud reports with altitude, aircraft type, intensity, and the raw PIREP string.
aviation_get_advisories	Get active domestic SIGMETs for a region. Returns hazard type (CONVECTIVE, TURBULENCE, ICING, IFR), severity, altitude range, valid period, polygon coordinates, and raw text.

Prompts

Prompt	Description
aviation_preflight_brief	Structure a preflight weather briefing for a flight, calling the tools above in sequence and synthesizing a weather-risk summary.

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Capability reference

aviation_find_stations _tool

• Look up one or more stations by identifier (up to 20 per call) — a lookup matches the registry's own ID, which for an airport is its 4-letter ICAO ID; a 3-letter IATA code never resolves, though each record includes its IATA/FAA aliases when available
• Discover stations within a geographic bounding box, or list stations for one of the 50 US states or DC via two-letter USPS code
• Returns data_types (METAR, TAF, etc.) so agents can confirm what's available before querying
• Every result states whether the upstream 400-row cap cut it; limit (1–400) bounds how many stations a bbox or state search returns, ordered by ICAO identifier ascending with identifier-less stations last — rejected alongside station_ids, since that mode already names the set
• An ID lookup names every identifier that resolved to nothing, separating a 3-letter IATA code (never resolves) from an identifier the registry simply does not list
• Whitespace around an ID is trimmed rather than failing the batch; only an empty or whitespace-only entry is rejected

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aviation_get_metar _tool

• Accepts 1–10 ICAO station IDs per call; hours (1–12) is a lookback window, not a row limit — every observation inside it is returned
• Flight category (VFR/MVFR/IFR/LIFR) returned directly from the AWC API; decodes wind, visibility, present weather, and cloud layers alongside the raw METAR string
• Ceiling reports both height and kind (measured, or indefinite for vertical visibility into an obscuration) — sky_condition distinguishes a reported clear sky from an unreported one when clouds is empty
• metar_type distinguishes routine METAR from special SPECI observations
• Every batch reports which requested stations came back, naming missing IDs with recovery guidance

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aviation_get_taf _tool

• Accepts 1–4 ICAO station IDs per call
• Structured forecast periods with change types (FM, TEMPO, BECMG) and probabilities; weather decoded group by group beside the raw groups
• Forecast obscurations keep their layer and carry the vertical visibility into them, rather than reading as clear sky; sky_condition distinguishes an unamended period from a stated clear sky
• Low-level wind shear (WS020/20040KT) decoded to the shear-layer top and forecast wind at that height
• valid_from / valid_to in ISO 8601 for time comparisons
• Every batch reports which requested stations came back, naming missing IDs with recovery guidance

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aviation_get_pireps _tool

• station_id + distance_nm (10–500 nm, 100 when omitted) for radial search, or bbox for area search — mutually exclusive
• altitude_min_ft / altitude_max_ft filter to a cruise-altitude band (min must not exceed max); a report with unknown altitude is dropped once either bound is set
• min_intensity (lgt / mod / sev) restricts to reports carrying a turbulence or icing layer at that intensity or above — a matching report still carries its lighter layers
• Turbulence and icing arrays include up to two layers per report; icing layers the API synthesized for a report that never mentioned ice are dropped
• Every result states whether the upstream 400-row cap cut it, and limit (1–400) bounds how many reports come back, ordered by recency
• PIREPs are sparse by nature — absence of reports does not mean smooth conditions

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aviation_get_advisories _tool

• advisory_type: sigmet or all (default) — both return the active SIGMET set
• hazard filter (CONVECTIVE, TURBULENCE, ICING, IFR) applied upstream by AWC; bbox filtered client-side by polygon overlap
• AIRMETs are not served — the upstream feed carries domestic SIGMETs only, and a request for one (or its MTN OBSCN / SURFACE WIND / LLWS hazards) is rejected with guidance rather than answered with SIGMETs
• An empty result is a valid fair-weather state, and names what emptied it — nothing active, no advisory carrying the hazard, or none intersecting the bbox — so a filter that needs broadening isn't mistaken for quiet weather

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aviation_preflight_brief _prompt

• Arguments: departure_icao and destination_icao required; alternates (comma-separated ICAOs), departure_time (ISO 8601 UTC), cruise_altitude (feet MSL), and route_waypoints (semicolon-separated lat,lon pairs) optional
• Calls aviation_get_metar, aviation_get_taf, aviation_get_pireps, and aviation_get_advisories in sequence, chunked to each tool's station-per-call limit
• departure_time selects the TAF forecast period the briefing is read against; cruise_altitude bounds the PIREP search to a ±3,000 ft band; route_waypoints become the advisories bbox, widened by 1° on each side
• Omitting any of the three still generates the briefing, naming the assessment it could not make
• Reports weather risk rather than a go/no-go recommendation — that decision needs pilot, aircraft, and operational-minima context this server does not hold

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Features

Built on @cyanheads/mcp-ts-core: stdio and Streamable HTTP transports, pluggable auth (none / jwt / oauth), swappable storage (in-memory, filesystem, Supabase, Cloudflare KV/R2/D1), structured logging with optional OpenTelemetry tracing.

Aviation-weather-specific:

• Keyless — no API key or authentication required; all data is from the public AWC Data API
• Single service (aviation-weather-service) with retry + exponential backoff for the keyless public endpoint
• Raw coded strings (raw_metar, raw_taf, raw_pirep, raw_text) surfaced alongside decoded fields so agents have both layers
• State→bbox table enables US-state station queries that the AWC API doesn't natively support
• Server-level instructions field surfaces the "not an official briefing" safety disclaimer to all clients on initialize

Agent-friendly output:

• Discriminated output — flight category (VFR/MVFR/IFR/LIFR) as a typed string field, so agents branch on it without parsing ceiling and visibility
• Structured error contracts — typed reason fields with recovery hints (e.g., "Verify ICAO IDs with aviation_find_stations")
• Partial-result reconciliation — batch tools report requested / returned / missing / partial fields, so a short batch is never mistaken for full coverage
• Workflow sequencing — the aviation_preflight_brief prompt encodes the correct METAR → TAF → PIREPs → advisories sequence, chunks each step to the tool's station limit, and names the assessments it could not make

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Getting started

Public Hosted Instance

A public hosted instance is available at https://aviation-weather.caseyjhand.com/mcp. Add it to your MCP client configuration:

{
  "mcpServers": {
    "aviation-weather": {
      "type": "streamable-http",
      "url": "https://aviation-weather.caseyjhand.com/mcp"
    }
  }
}

Self-Hosted / Local

Add the following to your MCP client configuration file.

{
  "mcpServers": {
    "aviation-weather": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/aviation-weather-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with npx (no Bun required):

{
  "mcpServers": {
    "aviation-weather": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/aviation-weather-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with Docker:

{
  "mcpServers": {
    "aviation-weather": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "ghcr.io/cyanheads/aviation-weather-mcp-server:latest"
      ]
    }
  }
}

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp

Prerequisites

• Bun v1.4.0 or higher (or Node.js v24+).
• No API key required — the AWC Data API is fully public and keyless.

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/aviation-weather-mcp-server.git

2. Navigate into the directory:

cd aviation-weather-mcp-server

3. Install dependencies:

bun install

4. Configure environment:

cp .env.example .env
# edit .env if you need to override AWC_BASE_URL or AWC_TIMEOUT_MS

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Configuration

Variable	Description	Default
AWC_BASE_URL	Base URL for the NWS AWC Data API.	https://aviationweather.gov/api/data
AWC_TIMEOUT_MS	Per-request timeout in milliseconds (1000–60000).	10000
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for HTTP server.	3010
MCP_SESSION_MODE	HTTP session handling: auto (resolves to stateful), stateful, or stateless. The server declares stateless in code — no tool here needs a multi-round-trip input — and the shipped .env.example and Docker image pin the same value. Setting this overrides the declaration.	stateless
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424).	info
OTEL_ENABLED	Enable OpenTelemetry instrumentation.	false

See .env.example for the full list of optional overrides.

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Running the server

Local development

• Build and run:

  bun run rebuild
  bun run start:stdio
  # or
  bun run start:http
  

• Run checks and tests:

  bun run devcheck   # Lint, format, typecheck, security
  bun run test       # Vitest test suite
  bun run lint:mcp   # Validate MCP definitions against spec
  

Docker

docker build -t aviation-weather-mcp-server .
docker run --rm -p 3010:3010 aviation-weather-mcp-server

The Dockerfile defaults to HTTP transport, stateless session mode, and logs to /var/log/aviation-weather-mcp-server. OpenTelemetry peer dependencies are installed by default — build with --build-arg OTEL_ENABLED=false to omit them.

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Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools/prompts and inits services.
src/config	Server-specific env var parsing (AWC_BASE_URL, AWC_TIMEOUT_MS).
src/services/aviation-weather	AWC Data API client — HTTP fetch, retry with exponential backoff, response normalization.
src/mcp-server/tools	Tool definitions (*.tool.ts).
src/mcp-server/prompts	Prompt definitions (*.prompt.ts).
tests/	Unit and integration tests mirroring src/.

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Development guide

See CLAUDE.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic
• Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage
• Register new tools and prompts via the barrels in src/mcp-server/*/definitions/index.ts
• Wrap external API calls: validate raw → normalize to domain type → return output schema; never fabricate missing fields

Not an official preflight briefing. Data from the AWC is informational only. Real flight planning requires an authorized source (e.g., Leidos/1800wxbrief.com). The server surfaces this disclaimer via its instructions field sent on every initialize.

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Contributing

Issues are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

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License

Apache-2.0 — see LICENSE for details.