Watch, warning, advisory: what each one is asking you to do

A watch means conditions are favourable for dangerous weather and it is time to get ready. A warning means that weather is now happening, or is about to, and the time for getting ready has passed. An advisory sits below both: expect disruption rather than danger.

Those three words come from the National Weather Service, and they are not three volumes of the same alert. They answer different questions.

What each one actually means

A watch is about possibility. Forecasters can see the ingredients coming together somewhere in a region, but not yet where, or whether. It goes out early, sometimes many hours ahead, and it covers a lot of ground.

A warning is about confirmation. The weather is occurring, imminent or likely, in a defined place. It arrives with less notice because it waits for something a watch cannot offer, which is knowing where.

An advisory covers conditions the National Weather Service describes as less serious than warning conditions, but still significant enough to cause real inconvenience, and hazardous if treated carelessly. Freezing drizzle on a commute is the everyday example.

Why a watch covers more ground than a warning

This one trips people up, because a bigger area on the map looks like a bigger emergency. It usually means the opposite.

There is a trade between how early an alert can be issued and how precisely it can be placed. Early means vague, because nobody yet knows which counties will be hit. Precise means late, because precision comes from watching the thing actually develop. A watch accepts uncertainty about location in exchange for warning you sooner.

So a watch spanning half a state, upgraded hours later to a warning over three counties, is not the threat shrinking. It is the forecast getting sharper.

The part people get wrong

The common misreading is to treat a warning as a watch with more urgency attached, and to respond by watching more closely.

But closer attention was already the right response to the watch. The warning is asking for something different. It is asking you to use the plan that the watch gave you time to make. That is why there are two words rather than one word and a severity score.

The National Weather Service publishes specific guidance for each hazard, and that guidance, rather than anything written here, is what a decision should rest on.

Where a weather app fits

An app does not issue warnings. It relays what the official authority has already issued, and what it can usefully do is make that legible before you have to go looking for it.

That is the job Ora Weather takes on when conditions turn severe. Its severe weather alerts follow the official classifications from the National Weather Service in the United States, and equivalent authorities in other markets, so what appears on your phone matches what the authority actually said rather than a rewording of it. While something is developing, it tells you what is happening, what to do, and when it ends. Once the event passes it sends a follow up all clear, so you find out it is over instead of having to check.

The goal is an alert that arrives because it changes your decision, rather than because something technically qualified for one.

The short version

A watch says this could happen here, so get ready. A warning says this is happening here, so act on it. An advisory says today will be more awkward than usual.

When you are not sure which one you are looking at, check how much time it implies you have. That is usually the difference.