Storm Front

The problem

Hundreds of alerts, and most of them have no shape

The National Weather Service publishes every active alert as one public feed, and Iowa State University publishes the national radar as map tiles. Both are open to a browser. The hard part is what the feed does to you the first time: most alerts arrive with no polygon at all, there is no way to ask for a smaller page of it, and the most severe alert is not always the most urgent one.

Watch it work

Episode 3 — Storm Front (6:15)

Two public feeds end to end: where the alerts and the radar live, the request the app actually makes, the three details that cost the most time, and the map they turn into.

What it covers

Two feeds, three details, one map

• The alerts: one request to the NWS alerts API returns every active alert in the country as GeoJSON, with open CORS headers so a browser can call it directly.
• The one thing it asks of you: send an empty User-Agent and the endpoint answers 403. A browser always sends one; a script on your server does not, until you set it.
• The radar: Iowa State University's Iowa Environmental Mesonet caches the NEXRAD base-reflectivity mosaic as open XYZ tiles, regenerated about every five minutes.
• Detail one, the missing shapes: roughly eight in ten active alerts are zone-based and arrive with geometry: null. Storm Front counts every one of them in its stats and lists, and draws only the ones with a real polygon.
• Detail two, no page size: add limit=50 and the endpoint answers HTTP 400. You take the whole feed, or you filter it after it arrives.
• Detail three, severity is not urgency: every alert carries CAP severity, urgency and certainty as three separate fields. Storm Front sorts by severity, then urgency, then the soonest end.
• How it becomes a map: two layers, two clocks, one view. Every five minutes the alerts are refetched and the radar layer is replaced, not changed in place; the fresh layer goes in underneath before the stale one is removed, so the radar never blinks.

What it does not do

• No history — Storm Front shows what is active now, not past alerts or archived radar.
• No shapes for zone alerts — alerts that name counties or marine zones are listed, but never drawn as invented polygons.
• Not a warning service — it shows the public NWS feed. For safety decisions, follow your local National Weather Service office.

Where the data comes from

Every source in the episode

• NWS alerts API — weather.gov/documentation/services-web-api
• NWS disclaimer (public domain) — weather.gov/disclaimer
• Iowa Environmental Mesonet tile services — mesonet.agron.iastate.edu/ogc/
• IEM disclaimer (public domain, credit requested) — mesonet.agron.iastate.edu/disclaimer.php
• Source sheet with every endpoint — allthingsspatial.io/pages/sources.html

Both feeds are in the public domain. The alerts are a work of the United States government; the Iowa Environmental Mesonet asks to be credited, so attribution sits in the Storm Front footer and its About dialog.