How It Works

NWS publishes a warning. alertq sees it within 30 seconds and finds the places inside it. onNAV hands each phone to Apple.

1. alertq. One poller for the whole country, in almanac.
2. onNAV. Delivery stays on onNAV’s account, with onNAV’s Apple key.

The warning, not the county

NWS draws a severe warning as a shape around the storm. Most apps still ring the whole county. NWS’s own studies found the shapes cover about 70% less ground. Drag Mom’s house and see who rings.

Home

Mom’s

Drag Mom’s house, or tap the map

An app that alerts by county

Rings

Wrong: the county and the warning disagree here.

onNAV Storm

Tells her: “4 mi from a warning”

© Mapbox © OpenStreetMap. The warning is made up; the county line is simplified. Try the southwest corner, where the warning crosses into the next county.

alertq, in almanac

A new Worker beside stormq, seaq and tideq, at alertq.almanac.observer.

1. Polls NWS every 30 seconds for every active alert in the US: one request to api.weather.gov/alerts/active, about 112 KB compressed on a quiet day. That’s the rate NWS asks for.
2. Keeps only what’s new or changed, so an update to a warning is an update, not a second alarm.
3. Matches places. A severe warning comes with its shape: one test per place. Everything else names forecast zones and counties, looked up once for each place when it’s saved.
4. Answers by place, like every almanac service, so any app can ask what’s in effect here. Storm, MarNav, or the next one.

Delivery, on onNAV’s account

Pushes come from a small Worker on onNAV’s own Cloudflare account. It holds onNAV’s Apple key and the list of phones, and listens to alertq for changes. The data is shared; the users are onNAV’s.

• What a phone sends: a push token, and each place’s point rounded to about 1 km, with the levels it wants. No name, no email, no account, no history.
• Straight to Apple. No OneSignal. A big outbreak fans out through a queue, because a Worker gets six connections at a time.
• One ring per warning. Updates change the banner and the countdown; they ring again only if the warning grows to cover somewhere new.

When something fails

Anything we host makes the app better, never the only way to get an answer.

• almanac or the push Worker is down: pushes stop. The app asks NWS itself whenever it’s open, and in the background when iOS allows, and still shows every warning.
• NWS is slow: nothing beats NWS. On August 12, 2026 a failed upgrade inside NWS delayed warnings to apps, TV and phones by up to 20 minutes. Storm always says how old its news is.
• No signal: the last warnings stay on screen with their end times, so an expired one says so.

What it builds on

The data

NWS, NOAA and APNs cost nothing. almanac runs on Cloudflare’s Workers plan, $5 a month. WeatherKit comes with the developer account. The real costs are the map, and our time.

In the app

The same shape as our other SwiftUI apps: one app state of observable parts, small operations for every side effect, and providers as the only code that knows a wire format.

• AlertProvider is the only code that knows alertq’s answer, and NWS’s for when it asks NWS directly.
• The shape test runs in alertq and on the phone from one set of test cases, so the two can’t disagree about who’s inside a warning.
• The countdown on the Lock Screen starts from the push and ends at the warning’s end time, even if nothing else arrives.
• Widgets draw what the app published and never fetch, so a widget can’t disagree with the app.

Risks

Sources

• NWS API and alerts; sizes measured October 31, 2026
• Storm-based warnings and the ground they save, Iowa State
• What Wireless Emergency Alerts send
• MRMS on AWS and SPC’s outlooks
• workerd #4841: Apple’s push service from a Worker
• The August 12, 2026 delay
• Downloads during Winter Storm Fern

onNAV Storm • A pitch for onNAV, October 2026