How Tornado and Severe-Storm Warnings Work (Watch vs. Warning)

Few pairs of words cause more confusion — or get more people hurt — than "watch" and "warning." They sound almost interchangeable. They are not. One buys you hours; the other gives you minutes. Getting the difference straight is genuinely the most useful severe-weather knowledge you can have.

You can see live severe-weather alerts on the LEV map by switching on the Storm Warnings layer. The tilted boxes it draws are the actual warning polygons issued by forecasters, color-coded by severity.

Watch vs. Warning: the one distinction that matters

Here's the rule, and it's worth memorizing:

• A WATCH means: be ready. Conditions are favorable for severe storms or tornadoes to develop across a broad area over the next several hours. A watch can be issued under a blue sky. It covers many counties. Nothing has happened yet — but the ingredients are in place, so this is your cue to plan, stay near a weather source, and know where you'd shelter.

• A WARNING means: act now. A tornado or severe storm has actually been spotted or detected on radar and is happening in a specific, smaller area right now. This is not a heads-up; it's a take-cover instruction.

A handy way to remember it: a watch is the ingredients on the counter; a warning is the cake in the oven. Watch comes first and is large and vague; warning comes second and is small and urgent.

Why warnings are tilted boxes, not counties

If you look at the Storm Warnings layer, you'll notice warnings are odd, tilted rectangles rather than neat county shapes. That's deliberate and fairly recent.

Warnings used to cover entire counties. The problem: a tornado might threaten one corner of a county while alerting everyone in it — including people 40 miles away who were never at risk. Over-warning makes people tune out, which is dangerous. So forecasters switched to storm-based polygons: a box traced around only the ground actually in the storm's path. It's more precise, it spares the people who aren't threatened, and its long axis roughly points the way the storm is heading. The map renders these polygons exactly as issued.

Severe thunderstorm warnings deserve respect too

It's easy to relax at the words "severe thunderstorm" — it's not a tornado, after all. Don't. A severe thunderstorm warning means damaging straight-line winds of at least 58 mph, hail at least an inch across, or both. Those winds can equal a weak tornado's and flatten trees and power lines across a much wider area. And the strongest severe storms can drop a tornado with very little notice. Treat a severe thunderstorm warning as the serious alert it is.

Where the warning comes from — and how the map fits in

Behind every warning is radar. Forecasters watch for the tell-tale signatures of a dangerous storm — the hook-shaped echo and the rotation that mark a possible tornado. (If radar is new to you, start with how to read weather radar, and note that an empty radar isn't always good news.)

This is where LEV does something a plain alert map can't. Switch on Storm Warnings together with the Radar layer and you can see the polygon and the storm cell it was drawn around in the same view — and adding the wind layer shows the steering flow pushing the whole system along. The warning tells you the threat; the radar and wind show you where it's going next.

The bottom line

Watch = be ready, hours out, big area. Warning = act now, minutes out, small area. A severe thunderstorm warning counts. When a polygon appears over you on the map, it was drawn around your ground specifically — and the right response to a warning is never to wait and see, but to move.

LEV is an awareness tool, not an official alerting service. Always follow your local emergency management and official weather service for life-safety decisions.