People wait for shuttle buses during a morning downpour at the Braddock Road Metro station on May 28 in Alexandria. (Matt McClain/The Washington Post)

Maybe it woke you in the middle of the night. Perhaps you were in a high-rise office or apartment building. Or maybe it did indeed save your life. The shrill, piercing shriek that our phones emit when a flash-flood warning is issued is unmistakable. It’s enough to make you leap out of your chair.

The warnings often urge action, advertising the need “to protect your life” and “move to higher ground immediately.”

But more often, what transpires falls short of what might be expected for an “emergency alert” to blare over our phones. That’s about to change. It’s part of a larger effort undertaken by the National Weather Service to improve alerts it produces and disseminates.

Cars caught in flash flooding off Glebe Road in Alexandria on July 8. (Paul Duggan/The Washington Post)

When it comes to flash-flood warnings, “there’s going to be a significant decrease in the number of wireless emergency alerts,” said Daniel Roman, a hydrologist with the National Weather Service helping spearhead an effort to simplify weather warnings and communication to the public.

“Since there are going to be fewer, they are being reserved for situations that are extremely life-threatening, when we want people to take action to protect their lives and property,” Roman said.

In a typical year, the National Weather Service issues about 4,000 flash-flood warnings, according to Roman. In years past, all would activate the emergency alert system and trigger wireless emergency alerts.

Now, forecast flash-flood events will be categorized into three tiers before a warning is issued: ordinary, considerable and catastrophic. The threat level will be included as a tag appended onto warning text. Meteorologists at the National Weather Service may also opt to include information on rainfall rates.

“You’ll only get a flash-flood warning on your cellphone when the threat is deemed to be considerable or catastrophic,” Roman explained. Only about 15 percent of warnings will reach this tier.

The catastrophic tag will correspond to a “flash flood emergency,” issued for the most dire threats that pose an immediate danger to life. A flash-flood emergency was issued July 8 for the District, Arlington and Alexandria when almost four inches of rain poured down in one hour.

“There are some offices that are already doing it, quite a number of them, actually,” Roman said. The rest of them were set to make the transition on or after Wednesday.

The NWS is also reshaping the format of flash-flood warnings to be “impact-based,” Roman said. “We’re expecting it to be easier to read, more closely focused on source, impact, location."

The flash-flood warning is one of 11 products issued by the NWS that are also broadcast via wireless emergency alerts. Others include the tornado warning, tsunami warning, hurricane warning and snow squall warning — alerts that require immediate action to protect public safety. Historically, the severe thunderstorm warning has not made the list. That, too, is being revised.

The alert simplification project is “looking across all of our hazards to identify areas where that emergency notification is needed,” said Eli Jacks, chief of forecast services within the National Weather Service’s Analyze, Forecast and Support office.

Jacks described the need to tap higher-end severe thunderstorm events into the wireless emergency alert system to better warn the public. After all, a violent thunderstorm complex with widespread 80 mph wind gusts such as a derecho will cause orders-of-magnitude more damage and have greater casualty potential than a slender EF0 tornado. The latter would warrant a tornado warning — and activate the squeal of your mobile phone. The former would not. Yet.

“Wind and hail [impacts] are pretty much universal,” Jacks said. “A certain amount of wind will do a certain amount of damage.” Preliminarily, it’s anticipated that the threshold for a wireless emergency alert will be 80 mph winds and/or large, destructive hail.

Jacks and his team are also probing possibilities of eliminating the “advisory” level of NWS products. But changing something that’s been around for so long won’t be easy.

“The advisory headline is being proposed for a general elimination, in favor of using descriptive headlines instead,” Jacks said.

Jacks said that eliminating advisories and retaining only watches and warnings is more in line with what’s useful to emergency managers.

“They have a prepare and act paradigm,” he explained. Watches generally connote the need for preparation, whereas warnings are hoisted when something is imminent or occurring — principally to spur action.

“In the bigger picture, we have been applying social science over the past five years based on years of feedback we’ve received,” Jacks said. “We’ve been focused so much on criteria. Now, we’re focusing on impact.”