emergency noun

• A serious situation or occurrence that happens unexpectedly and demands immediate action.

• A condition of urgent need for action or assistance. "a state of emergency."

• Sudden or unexpected appearance; an unforeseen occurrence; a sudden occasion.

Seems to meet the definition of an emergency to me!

They've got a whole city to alert, to protect their lives, in a dynamic situation occurring in real time. Whilst they provided 2 hours notice, they were transporting the explosive shortly before travel peak time.

Other methods of media communication couldn't reliably ensure the vast majority of the public received the notification in time. Especially when most people would be working, and often don't have access to those methods until they finish or are on break.

Was an appropriate use of the emergency alert system.