@Cyanheads/Nws Weather Server

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Overview

US weather data from the National Weather Service API (api.weather.gov). Get forecasts, active alerts, current observations, forecast-office narrative products, and zone-level text forecasts for any coordinate in the 50 states, US territories, and adjacent marine areas. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.

Tools

Tool	Description
nws_get_forecast	7-day or hourly forecast for coordinates. Resolves NWS grid internally.
nws_search_alerts	Active weather alerts filtered by area, point, zone, event, severity, urgency, certainty, and status.
nws_get_observations	Current conditions by coordinates (nearest station) or station ID.
nws_find_stations	Nearby observation stations sorted by distance with bearing.
nws_list_alert_types	All valid alert event type names for filter discovery.
nws_get_office_discussion	Latest narrative product (AFD, HWO, ZFP, SPS) from a Weather Forecast Office.
nws_get_zone_forecast	Text forecast periods for a public NWS forecast zone.

Resources

Resource	Description
nws://alert-types	Static list of all valid NWS alert event type names.

Also reachable via the nws_list_alert_types tool, for MCP clients that don't support resources.

Capability reference

nws_get_forecast _tool

• Default returns named 12-hour periods (14 total, ~7 days)
• Hourly mode returns 48 one-hour periods per page with dewpoint and humidity — the upstream feed carries ~156, and the pre-page total (totalCount, against this page's shown) plus a truncation notice are surfaced in the enrichment block
• Pass the returned nextCursor back as cursor to reach the remaining periods; it is omitted on the last page
• Coordinates resolve to NWS grid internally via /points
• Formatted timestamps use the resolved local time zone
• Returns forecast zone and county zone codes for chaining into nws_search_alerts

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nws_search_alerts _tool

• area, point, zone, region_type, and region are mutually exclusive location filters (at most one, or none for a national search); event matches case-insensitively and partially ("tornado" matches both watches and warnings); status defaults to Actual (also Exercise, System, Test, Draft)
• A blank string filter or an empty-array filter is rejected rather than silently widened to an unfiltered search
• Area/point/zone shape is validated locally before the API call, failing fast with typed invalid_area_code / invalid_point / invalid_zone reasons instead of a raw upstream 400
• limit (1-25, default 25) pages results; totalCount is the full distinct-alert count (duplicates collapsed on id) against shown, and nextCursor continues — pages are contiguous only within one response, since every call re-fetches the live feed
• Each affectedZones entry carries its zone type (forecast/county/fire) so callers know which codes chain into nws_get_zone_forecast
• CAP message-lifecycle fields (sent, effective, status, messageType, references) are distinct from the hazard's own onset/ends

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nws_get_observations _tool

• Look up by coordinates (resolves nearest station) or station_id directly; a blank/whitespace-only station_id is rejected rather than silently falling back to coordinates
• Dual-unit display on every measurement: F/C, mph/km/h, inHg/hPa, mi/km
• Observation timestamps use the station's local time zone when known
• Flags observations older than 2 hours with a staleness notice, and warns separately when most measurements are unavailable from the station

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nws_find_stations _tool

• Sorted by haversine distance from the query point; each result carries distance (km), bearing, zone codes, elevation, and time zone
• Optional limit (1-50, default 10) sizes the page; totalCount reports every station near the point and holds steady across pages, while shown is the size of this page
• Pass the returned nextCursor back as cursor to reach stations beyond the page; it is omitted on the last page
• Useful for finding station IDs for nws_get_observations

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nws_list_alert_types _tool

• Returns the full set of event types the NWS API recognizes (e.g., "Tornado Warning", "Heat Advisory")
• Use to discover valid values for the event filter in nws_search_alerts

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nws_get_office_discussion _tool

• office: 3-letter WFO code (e.g., "SEW" for Seattle) — returned as the office field by nws_get_forecast
• product_type: AFD (default, forecaster reasoning and model analysis), HWO (1-7 day hazard outlook), ZFP (zone-by-zone text forecast), SPS (short-fuse advisory)
• Returns productText plus issuanceTime, issuingOffice, productName, productCode, wmoCollectiveId
• An unknown office, or a valid office with no current product of the requested type, fails with a typed no_products error and recovery guidance — NWS answers HTTP 200 with an empty list rather than a 404

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nws_get_zone_forecast _tool

• zone_id: forecast zone code (e.g., "WAZ315") — returned by nws_get_forecast (forecastZone), nws_find_stations (forecastZone column), and nws_search_alerts (the code of an affectedZones entry with type: "forecast")
• Returns named periods (e.g., "Today", "Tonight", "Monday") with narrative text from local forecasters
• Completes the alert-to-forecast chain: look up alert zones, then retrieve zone forecasts
• County (XXC###) and fire zone codes are not supported here — NWS publishes no text forecast for them, though they remain valid values for the zone filter on nws_search_alerts; an unsupported or unknown zone fails with a typed zone_not_found error

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nws://alert-types _resource

• Static list of all valid NWS alert event type names, returned as application/json
• Duplicates nws_list_alert_types for MCP clients that support resources rather than tools
• Cached publicly for 1 hour — NWS revises this vocabulary on the order of years
• No parameters

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.

NWS-specific:

• Sends the required User-Agent header automatically (configurable via NWS_USER_AGENT) — NWS returns 403 without one
• Automatic coordinate-to-grid resolution via /points, cached for 1h since grid cells rarely change
• Request timeouts plus retry/backoff for transient NWS API failures
• Zero-auth access — no API keys required
• Dual-unit display for observations (F/C, mph/km/h, inHg/hPa, mi/km)

Agent-friendly output:

• Provenance — forecast, observation, and station responses echo office codes, time zones, and forecast/county zone codes so agents can chain directly into nws_get_office_discussion, nws_get_zone_forecast, and nws_search_alerts without re-deriving them
• Guidance over silence — empty, truncated, or cursor-past-end results carry a notice naming the cause and the concrete next step, rather than an empty array or a bare page
• Discriminated output contracts — zone type (forecast/county/fire), CAP status/messageType distinct from hazard onset/ends, and typed error reasons (invalid_area_code, no_products, zone_not_found, …) — callers branch on data, not string parsing
• Response shaping — upstream single-unit floats are normalized into dual-unit pairs (F/C, mph/km/h, inHg/hPa, mi/km) and rounded to match what format() renders, so structured and text output agree

Getting started

Public Hosted Instance

A public instance is available at https://nws.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:

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

Self-Hosted / Local

Add the following to your MCP client configuration file.

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

Or with npx (no Bun required):

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

Or with Docker:

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

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

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

Prerequisites

• Node.js v24+ or Bun v1.4+

Installation

1. Clone the repository:

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

2. Navigate into the directory:

cd nws-weather-mcp-server

3. Install dependencies:

bun install

Configuration

Variable	Description	Default
NWS_USER_AGENT	User-Agent for NWS API requests. The API requires this header.	(nws-weather-mcp-server, ...)
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for HTTP server.	3010
MCP_HTTP_HOST	Hostname for HTTP server.	127.0.0.1
MCP_SESSION_MODE	HTTP session mode: stateful, stateless, or auto.	stateless
MCP_LOG_LEVEL	Log level: debug, info, notice, warning, error.	info

See .env.example for the full list including auth, storage, and OpenTelemetry options.

Running the server

Local development

• Build and run the production version:

  # One-time build
  bun run rebuild
  
  # Run the built server
  bun run start:http
  # or
  bun run start:stdio
  

• Run checks and tests:

  bun run devcheck     # Lints, formats, type-checks
  bun run test         # Runs test suite
  

Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools and the resource.
src/mcp-server/tools/definitions/	Tool definitions (*.tool.ts).
src/mcp-server/resources/definitions/	Resource definitions (*.resource.ts).
src/services/nws/	NWS API client and response types.
src/config/	Environment variable parsing and validation with Zod.
tests/	Unit and integration tests mirroring src/.

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 domain-specific logging, ctx.state for storage
• Add new tools/resources to the barrel exports and the createApp() arrays in src/index.ts
• Wrap NWS API calls: validate raw JSON → normalize to domain types → return the output schema; never fabricate missing fields

Contributing

Issues are welcome. Run checks before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.