Subscribe to live alerts over MQTT

You will write a short Python program that connects to the public WxAlerts MQTT broker, subscribes to the alerts for one county and prints each alert as it arrives. You need Python 3 and no account. Install the MQTT library first, version 2.0 or newer:

pip install paho-mqtt

1. Write the client

Save this as alerts.py. It subscribes to El Dorado County, California, whose SAME code is 006017. The broker’s credentials, wxalerts and wxalerts, are public on purpose and the account is subscribe-only.

import json
import paho.mqtt.client as mqtt

def on_connect(client, userdata, flags, reason_code, properties):
    # One county: El Dorado, California.
    client.subscribe("wxalerts/nws/v1/same/006017/#", qos=1)

def on_message(client, userdata, msg):
    if not msg.payload:
        print("ended:", msg.topic)     # tombstone, not JSON
        return
    alert = json.loads(msg.payload)
    print(msg.topic)
    print(alert["event"], "|", alert["headline"], "| ends", alert["ends"])

client = mqtt.Client(
    mqtt.CallbackAPIVersion.VERSION2,
    client_id="my-unique-client",
    transport="websockets",
)
client.username_pw_set("wxalerts", "wxalerts")
client.tls_set()
client.on_connect = on_connect
client.on_message = on_message
client.connect("mqtt.wxalerts.org", 443)
client.loop_forever()

The client talks MQTT over a WebSocket on port 443 with TLS, which is the only way into the broker. Change my-unique-client to a name of your own, because two clients that share a client ID kick each other off.

2. Run it

python3 alerts.py

A live alert is retained on the broker, so the alerts already in effect for the county arrive the moment you subscribe. Each one prints its topic and a line about the hazard:

wxalerts/nws/v1/same/006017/0004
Winter Storm Warning | Winter Storm Warning issued November 12 at 12:33AM PST until November 14 at 10:00AM PST by NWS Reno NV | ends 2026-11-14T18:00:00+00:00
wxalerts/nws/v1/same/006017/0032
Lake Wind Advisory | Lake Wind Advisory issued November 11 at 11:52AM PST until November 13 at 10:00AM PST by NWS Reno NV | ends 2026-11-13T18:00:00+00:00

If the county has no alert in effect, nothing prints. Leave the program running: a new alert prints when the NWS issues it, and ended: followed by a topic prints when one ends. Stop it with Ctrl+C.

You now have a client that is told about alerts instead of asking for them. To make it reliable enough to leave running, see Build a reliable MQTT client.