A Flash Flood Emergency is the highest level of flash flood warning the National Weather Service (NWS) issues. It is a headline placed in a Flash Flood Warning or follow-up statement for exceedingly rare situations when a severe threat to human life and catastrophic damage from a flash flood is imminent or ongoing.
How it ties to the warning tags
Flash Flood Warnings carry a damage threat tag. The base level, with no tag, is used most of the time. CONSIDERABLE is used rarely, and CATASTROPHIC is used exceedingly rarely, when a flash flood threat to life and catastrophic damage is occurring or imminent.
The NWS says the CATASTROPHIC tag equates to a headline and added language for a Flash Flood Emergency. In the warning text, the national directive has the headline name the place, in the form A FLASH FLOOD EMERGENCY FOR followed by the geographic area.
What it means for alerts
Because the emergency rides on the CATASTROPHIC tag, it meets the rule for Wireless Emergency Alerts (WEA), which the NWS limits to Flash Flood Warnings tagged CONSIDERABLE or CATASTROPHIC. A follow-up Flash Flood Statement that raises the threat to CATASTROPHIC also triggers a WEA.
NOAA describes catastrophic events as violent flash floods that extraordinarily threaten lives and cause disastrous damage.
How it compares with other emergency headlines
The idea parallels the Tornado Emergency, another rare headline reserved for the most dangerous end of a warning type. Both exist so the top tier stands out from the everyday warnings that share the same product name.
What it does not tell you
The headline is about the threat, not a measured flood depth or an exact boundary of the worst water. Conditions inside the named area can differ block by block, and forecasters may add the headline while information is still incomplete.
An emergency could also come from causes other than rain, since flash floods can include dam failures and ice jam releases. The text of the statement, not the headline alone, explains the cause and the locations at greatest risk.