Alert Changes

A weather alert is not a static object. It may be updated one or more times as the weather event develops. Based on the messageType (the nature of the alert message), you can determine whether the current advisory is the initial release or an update to a previous advisory.

messageType can be:

• alert: An initial alert message
• update: An update that replaces an earlier alert message
• cancel: A message that cancels an earlier alert

Alert#

alert indicates that a new alert has been issued for the first time.

For example:

id:              A
issuedTime:      10:00
messageType:     alert
supersedes:      []
eventType:       wind
severity:        minor
expireTime:      18:00

This begins a new alert lifecycle.

Update#

update indicates that a previously issued alert has changed. An update may modify its severity, affected area, expiration time, or other information.

For example:

id:              B
issuedTime:      13:00
messageType:     update
supersedes:      [A]
eventType:       wind
severity:        moderate
expireTime:      20:00

Alert B replaces alert A at 13:00. Its severity increases and its expiration time is extended. Alert A is no longer returned by the Alert API.

Cancel#

cancel indicates that an earlier alert has been canceled.

For example:

id:              C
issuedTime:      15:00
messageType:     cancel
supersedes:      [B]
eventType:       wind
severity:        moderate
expireTime:      16:00

Alert C replaces and cancels alert B at 15:00. Alert B is no longer returned by the Alert API. The cancellation message has its own expiration time, which defaults to one hour after issuance.