NWS Alerts - Polygon

Active National Weather Service watches, warnings and advisories that touch an area.

POST a GeoJSON Polygon or MultiPolygon (or a Feature wrapping one) in [lon, lat] order, up to 5,000 vertices. Every alert whose area intersects it is returned. Filters go in the query string, the same as the point endpoint.

Data source

Watches, warnings, advisories and statements from the National Weather Service, read from api.weather.gov/alerts/active every 60 seconds. New alerts are normally in this API within two minutes of NWS issuing them.

Matching

Storm-based alerts (tornado, severe thunderstorm, flash flood warnings and similar) match by the polygon NWS drew.
Zone-based alerts (winter storm, heat, wind, flood watches and most advisories) have no polygon. They match by the NWS public, county or fire zones they were issued for.

Lifecycle

An Update replaces the message it references. A Cancel ends it. Replaced and cancelled alerts are never returned as active.
A message that only cancels, upgrades or expires an event (VTEC action CAN, UPG or EXP) ends the earlier messages for that event and is not returned as active itself.
Cancel messages end the alert they refer to and are never returned as active. With include_expired they appear among ended alerts when they carry a polygon.
Alerts are removed once NWS drops them from its active feed or their ends time passes (expires when there is no ends).
Ended alerts are kept for 90 days. Use include_expired=true with since to see the ones that ended after that time. If more than 5,000 ended alerts fall near the area, only the most recently ended are checked and metadata.warnings says so.

Filters

event, severity, urgency, certainty, status (default Actual), message_type (default Alert,Update) and since. Each takes a comma-separated list. Results are ordered most severe first, then newest first.

Freshness

metadata.last_poll is the last successful read of the NWS feed. If it is more than 3 minutes old, metadata.warnings says so.

Authorization

Authorization<token>

Token-based authentication with required prefix "Token"

In: header

Query Parameters

certainty?string

Optional: CAP certainty. Comma-separated, any of: Observed, Likely, Possible, Unlikely, Unknown.

event?string

Optional: Comma-separated NWS event names, matched case-insensitively (e.g. Tornado Warning, Severe Thunderstorm Warning, Winter Storm Warning).

include_expired?boolean

Optional: Also return alerts that have expired, been cancelled or been replaced by an update and that ended at or after since (default the last 24 hours). Default false.

include_geometry?boolean

Optional: Add each alert's GeoJSON geometry: the storm-based polygon when NWS issued one, otherwise the union of its zones. Default false.

message_type?string

Optional: CAP message type. Cancel messages end an alert and are never returned as active. Comma-separated, any of: Alert, Update, Cancel. Default Alert,Update.

severity?string

Optional: CAP severity. Comma-separated, any of: Extreme, Severe, Moderate, Minor, Unknown.

since?string

Optional: Only active alerts sent at or after this ISO 8601 time (e.g. 2026-10-04T12:00:00Z). Must be within the 90-day retention window. With include_expired=true, ended alerts are returned when they ended at or after this time, however long ago they were sent (default the last 24 hours).

Formatdate-time

status?string

Optional: CAP status. Comma-separated, any of: Actual, Exercise, System, Test, Draft. Default Actual.

urgency?string

Optional: CAP urgency. Comma-separated, any of: Immediate, Expected, Future, Past, Unknown.

Request Body

TypeScript Definitions

Use the request body type in TypeScript.

type*string

Polygon, MultiPolygon, or Feature

Length1 <= length

coordinates?array<unknown>

GeoJSON coordinates, [lon, lat] order

geometry?

Polygon or MultiPolygon, when type is Feature

Response Body

`application/json`

curl -X POST "https://example.com/alerts/nws/polygon/?event=Tornado+Warning%2CSevere+Thunderstorm+Warning" \  -H "Content-Type: application/json" \  -d '{    "type": "string"  }'

{  "location": {    "bbox": [      -85.9,      31.8,      -85.4,      32.1    ]  },  "count": 1,  "alerts": [    {      "id": "urn:oid:2.49.0.1.840.0.89401f5530d0ca5022fcca4bb3ed2ad71a203663.001.1",      "event": "Flash Flood Warning",      "headline": "Flash Flood Warning issued October 4 at 9:34PM CDT until October 5 at 12:30AM CDT by NWS Birmingham AL",      "nws_headline": null,      "description": "The National Weather Service in Birmingham has issued a\n\n* Flash Flood Warning for...\nNorthern Barbour County...",      "instruction": "Be especially cautious at night when it is harder to recognize the\ndangers of flooding.",      "severity": "Severe",      "urgency": "Immediate",      "certainty": "Likely",      "status": "Actual",      "message_type": "Alert",      "category": "Met",      "response": "Avoid",      "sender": "w-nws.webmaster@noaa.gov",      "sender_name": "NWS Birmingham AL",      "area_desc": "Barbour, AL; Bullock, AL; Pike, AL",      "ugc": [        "ALC005",        "ALC011",        "ALC109"      ],      "vtec": [        "/O.NEW.KBMX.FF.W.0037.261005T0234Z-261005T0530Z/"      ],      "references": [],      "sent": "2026-10-05T02:34:00Z",      "effective": "2026-10-05T02:34:00Z",      "onset": "2026-10-05T02:34:00Z",      "expires": "2026-10-05T05:30:00Z",      "ends": "2026-10-05T05:30:00Z",      "geometry_source": "polygon",      "active": true,      "superseded_by": null,      "ended_at": null,      "end_reason": null,      "url": "https://api.weather.gov/alerts/urn:oid:2.49.0.1.840.0.89401f5530d0ca5022fcca4bb3ed2ad71a203663.001.1"    }  ],  "metadata": {    "source": "National Weather Service (api.weather.gov)",    "feed_updated": "2026-10-05T03:45:00+00:00",    "last_poll": "2026-10-05T03:49:11.929690+00:00",    "filters": {      "status": [        "Actual"      ],      "message_type": [        "Alert",        "Update"      ],      "include_expired": false    },    "processing_time_ms": 0.66  }}

NWS Alerts - Polygon

200application/json

400application/json

500application/json

503application/json

On this page

`application/json`

`application/json`

`application/json`

`application/json`