How the tracker works · Flex Weather Tracker

In short: the tracker doesn't know when a station closes. It knows the weather. For every station it gathers the active weather reports, looks for ground strikes within 6 miles, checks for tornado warnings, reads the nearest airport's report and estimates the chance of lightning close by in the next 20 minutes. It records every closure it sees and grades its own warnings afterwards. This page explains each step, how fresh the picture is on each plan, and where the method falls short.

Step 1: weather reports for each station's area

Every station starts with the weather reports and advisories currently active for the area around it. "Active" means started, not yet expired and not cancelled. Official warnings come from the National Weather Service in the United States, from Environment Canada in Canada, and from each country's national weather service elsewhere.

The reports are ranked by severity, and the most severe one decides the station's colour:

Red, "weather reports indicate a closed station", when the top report is one of the kinds the tracker treats as going with a closure: lightning within 6 miles, a tornado warning, an extreme wind warning or gusts above 50 mph, a heat index of 115°F or more, a wind chill of -40°F or colder, visibility under 100 feet, very bad air quality, or an incident at the station.
Amber, "weather advisories near the station", when something is active but below that level, such as lightning in the area, a wind or heat advisory, winter weather or a tornado watch.
Green when nothing is active.

Every report is shown in the tracker's own plain wording, so the same kind of event reads the same way everywhere.

Step 2: lightning within 6 miles

Lightning gets its own check, because it changes minute by minute and the tracker's rule for it is precise. The tracker takes strike reports from lightning networks, refreshes them every half minute and keeps the last 30 minutes. For each station it asks one question: has a ground strike landed within 6 miles? Strikes within 10 miles are flagged too, more loosely, as lightning in the area.

Only ground strikes count. Flashes that stay inside or between clouds are ignored, because the tracker's 6-mile rule is about strikes that reach the ground.
The tracker's all-clear is 30 minutes after the latest strike inside 6 miles. Each new strike inside that circle restarts the clock. Drivers commonly report that stations reopen on about the same clock; station leadership makes the call.

On the map, strikes from the last 30 minutes are drawn as marks that fade as they age, and the slider under the map replays them minute by minute.

Step 3: tornado warning shapes

Tornado warnings from the National Weather Service and Environment Canada are drawn as shapes (polygons) along a storm's expected path, which is much tighter than a whole county. The tracker checks whether each station's location falls inside an active warning's shape and puts a tornado icon over any that do. Tornado watches, which cover large areas where tornadoes are possible, show as advisories instead.

Step 4: the nearest airport's weather report

For each station the tracker also reads the latest report from the nearest airport within 25 miles. Airport weather stations measure the wind and gusts and record thunder heard and lightning seen. That shows what the wind is actually doing nearby, not just what was forecast. Outside the US and Canada, NOAA's forecast models add gusts and thunder for the hours ahead.

Step 5: the 20-minute "closing soon" forecast

Knowing a station is closed is useful. Knowing it's about to close is better. For stations with lightning in the area, the tracker estimates the chance of a ground strike within 6 miles in the next 20 minutes. It looks at:

the storm cells nearby on radar,
which way and how fast they're moving,
where recent strikes have landed, and whether they're getting closer.

The chance shows on the station's details. When it's high enough, the station is marked closing soon. This 20-minute prediction is expected to be right roughly three times in four. About one in four isn't followed by a closure, which is why the tracker calls a closure "likely", not certain.

On the paid plans, a "closing soon" heads-up can be sent for the stations you watch. It doesn't only come from the 20-minute prediction: a lightning or storm advisory at a station you watch sends one too, and so does a tornado warning whose shape covers the station. Before any heads-up is sent, the tracker waits a minute and checks that it still stands: the advisory or warning is still in force, or the prediction still says closing soon, or a strike has already landed within 6 miles.

The "three times in four" figure is for the 20-minute prediction only. The heads-ups from advisories and tornado warnings are graded separately, each kind on its own line of the accuracy page, and can do better or worse.

Step 6: recording every closure

Station statuses are worked out again about every 30 seconds. Every stretch of time a station reads closed is written down as one closure, with its start, its end and its cause: lightning, wind, heat, a tornado warning and so on. If a closure ends and comes straight back, it counts as the same closure rather than two.

Times the tracker wasn't watching, such as a restart, are noted too, so a quiet month can be told apart from a missed one, and a closure whose true start or end isn't known is marked uncertain.

That record builds the public closure history and its daily archive, each station's closures month by month in its details, and the counts of the most-closed stations over the last 3, 7, 14 and 30 days.

Step 7: grading the warnings

A prediction is only worth something if someone checks it. Every "closing soon" heads-up the tracker raises is written down, and 22 minutes later, a little longer than the 20-minute forecast it's checking, the tracker looks at whether the station actually closed in that time. Each heads-up ends up as a hit or a false alarm, along with how many minutes of warning it gave.

The results are published on the accuracy page, good and bad, with each kind of heads-up (the 20-minute prediction, lightning and storm advisories, tornado warnings) on its own line. The forecast's inputs are recorded the same way and checked against the strikes that followed, which is how its accuracy is measured and improved over time.

Other signals: incidents and driver reports

Not every closure is weather. Station incidents, such as a police matter at the site, come from police dispatch and local news reports and are worded vaguely on purpose. Signed-in drivers can also report a station closed or open from its details; the report shows beside the weather status for 30 minutes without changing it.

How fresh the picture is

The server works out every station's status about every 30 seconds. How often your screen catches up depends on the plan:

No account, or the free plan: every 6 minutes, on a shared clock that updates at the same moment for everyone. Free closure alerts are sent at those moments too, as a phone notification for your Main Station.
Pro: every minute, with alerts by email and notification for the stations you watch.
Ultra: live, every half minute.

By default, alerts pause between 9 PM and 3 AM local time, and a closure still going at 3 AM is sent then. Drivers who work nights can switch that window off in their account.

What the tracker can't do

It reads weather, not decisions. Station leadership decides closures. A red station can stay open, and a green one can close for something no weather report shows.
Lightning detection isn't perfect. Networks can miss strikes or place them slightly off, and a strike right around the 6-mile line can land on either side of it.
Data can be late or missing. When a source is slow or down, the status can lag behind what's happening.
Station locations come from public lists and can be off. If yours is missing or misplaced, the About page says how to tell us.
The forecast is a probability, and some closures come with little warning.

That's why the right way to use the tracker is as an early warning: a prompt to check the Flex app, look at the sky and plan your next half hour, not a final answer. The Flex Weather Tracker is independent and is not affiliated with Amazon, and the Flex app is the final word on your block.

Open the live map

How the tracker decides a station may be closed