It often starts with just one distant siren.
But soon, the air is filled with the sound of them, different pitches, different directions, different patterns.
What starts as a routine web post about a bit of traffic disruption suddenly takes on a new, dark and tragic character.
And you know you have a big story on your hands.
My friends at The Bath Chronicle are today chasing multiple angles on the biggest tragedy to hit the city for decades.
In my 19 years running the newsdesk there, there was nothing that could compete with the intensity and dramatic horror of yesterday’s tragedy in Weston.
I have to go back to my time at the Swindon Advertiser to find a tragedy of this magnitude.
There, I was part of a newsdesk team which covered two unspeakably sad crashes – both on the 13th of the month, both in 1991 – in which ten people and five people were killed.
These are occasions when this job of ours becomes very real.
Of course what we do is as nothing when compared to the gruelling, heart-breaking and utterly exhausting work of the emergency services at these times.
And yet we should be in no doubt about the importance of our role.
Not just in providing information, satisfying curiosity and sifting the truth from the rumours.
But also in trying to make sense of the senseless, in allowing a community to gather its thoughts and to support its wounded, and in enabling families whose lives have been torn apart to express their grief and gratitude.
In short, in finding the right things to say when words have failed most people.
There are many balancing acts to negotiate here: the relentless pursuit of new angles against the sensitivity of raw loss; the division of resources between this massive story and all the other ones still unfolding; and the different sorts of writing needed to do justice to a community in shock online and in print.
Knowing my friends in Bath as I do, I have little doubt that they’ll get it right.
And doing that – covering all the angles and issues, treating the victims as fully rounded people, and crafting the right words with the right pictures – is what good journalism is all about.
Thankfully, this sort of horror doesn’t happen every day, every week, every year or maybe even every decade.
All the more important, then, that we rise to the occasion when it does.