美国国家公共电台 NPR--Seeing a red flag warning in your weather app? Here's what to do（在线收听）

Seeing a red flag warning in your weather app? Here's what to do

Transcript

Spring is here, bringing with it warmer weather and, in many parts of the U.S., red flag warnings.

People in states from Minnesota to Maryland to Massachusetts saw those alerts on their weather apps this week. The notices warn of an increased risk of wildfires due to a combination of warm temperatures, low humidity and strong winds.

The National Weather Service (NWS) issues the warnings in conjunction with local and state agencies, explains NWS spokesperson and meteorologist John Moore.

"That means that the right amount of conditions are out there for the start of spread of wildfires," Moore says. "It also means critical fire weather conditions are occurring now or will be shortly ... So we tell people to exercise extreme caution if you're burning ... or doing anything with fire outside."

Though, he adds, it's important to practice good fire safety habits all the time, since wildfires don't only happen on red flag warning days.

The origin of the name is quite literal, says Tamara Wall, a research professor at the Desert Research Institute in Nevada.

"If there was a high fire danger, local fire stations would go and run a red flag up the flagpole," she says. "It was a very visual, kind of pre-mass communications way to signal to people in the ... area that it was a high-danger day."

Electronic red flags warn of risky conditions in the next 12 to 24 hours. They differ in timing from a fire weather watch, which warns of the possible development of those conditions in the next 72 hours.

Wall says the latter term was created to further differentiate between "warning" and "watch" in firefighters' radio communications. But it has ended up confusing many people, who wrongly assume that one is more severe than the other.

That assumption is likely due to the way the terms are used in other weather alerts — for example, a tornado watch means that tornadoes are possible in the area, while a tornado warning means that one has been sighted. Red flag warnings and fire weather watches can be for equally severe conditions, Wall says, it's just that a watch extends for a longer period of time.

"Fire is a little bit of a tough one, because unlike hurricane warnings or watches or other warning watch products, we don't know if it's really going to happen," Wall says.

Here's what else to know — and do — about these warnings.

What should you do if you get an alert?

A red flag warning is essentially a heads-up, Wall says.

People should prepare for a possible ignition or evacuation, like keeping their phones charged and making sure they know where their loved ones — especially people with disabilities or mobility issues — are during the day. They'll want to make a plan for what to do with any pets or livestock, too.

Before people leave home for the day they should make sure that all of their house and car windows are closed, and could even bring flammable materials like outdoor cushions inside the home or garage.

Other precautions included removing any dead shrubbery around your house that could maintain a fire, keeping your vehicle off dry grass and avoid using power equipment that creates sparks.

Wall says that fire management personnel will also take these warnings into account, like changing staffing numbers or preemptively moving resources into a certain region in case something happens. If there is a potential for an especially dangerous event, she says, local authorities may consider policy decisions like banning campfires or closing specific areas.

Moore says on red flag days, more than ever, "you don't want to be reckless with fire." So avoid doing things that could accidentally spark a wildfire, whether that's starting a bonfire, burning trash in the yard or flicking a cigarette out the car window.

"It's mainly telling folks ... to make preparations," Moore says. "If you were planning to do something that day, you probably should reschedule."

What are the criteria for a red flag warning?

The NWS says red flag events typically require a combination of critical fuel conditions — as determined by land management agencies — and critical weather conditions.

The primary criteria include relative humidity of 15% or less combined with either sustained surface winds or frequent gusts of 25 mph or more. Both conditions must occur simultaneously for at least three hours out of a 12-hour period.

Moore says the main considerations are wind speed, humidity and how dry the ground is, though the exact conditions vary by region.

Every year, each weather forecast office creates an annual operating plan (AOP) that lists out the criteria that they will use when deciding whether to issue a red flag warning or a fire weather watch, Wall explains.

"For example, 20% humidity in Florida is a very, very different potential fire weather situation than 20% humidity in Nevada," she adds.

Moore says the NWS takes the information and expertise of state and local partners into account when making those decisions.

"We can issue red flag warnings, but we can't issue burn bans or things of that nature, local restrictions, those are all up to the decisions of state and local authorities," he adds. "So we work closely with them to set those thresholds as well."

Where and when do we typically see them?

Red flag conditions can occur in any part of the country at any time of year.

"Almost anywhere has the potential for a non-controlled fire," Wall says.

There is some seasonality to them, she adds. Fire season begins in the southwest sometime around March and continues through the northern Rockies in August and September, while California typically has its fire season in the fall.

"They're pretty common across the country," Moore says. "From my experience as a meteorologist, every area that I've lived in has had red flag warning days."

Moore notes that there are natural variations in climate patterns and the warnings they require, so he can't necessarily say there's been an upward trend in red flag warnings in recent years.

But more people have access to weather information — whether through iPhone apps or social media posts — than ever before, which he sees as a good thing.

"We want more people to pay attention to the weather," Moore says. "And especially on days that could be impactful to not only yourself but to your community if you're not careful, we want people to be aware of it."

Will the warning system change?

Could a constant stream of red flag warnings and fire weather watches actually have the opposite effect, by potentially desensitizing people to the risk of fires?

Moore says there may be a risk that people will grow accustomed to these warnings, but they still serve an important purpose of heightening awareness about especially dangerous conditicons.

"Want to always reiterate to not do those [basic] things, whether it's dangerous weather conditions or not," Moore says. "But we want to add a little bit more to it as we remind people for those really dangerous days."

He acknowledges the confusion between the two terms and says that's "something that we're looking at internally."

Wall — who works closely with programs funded by the National Oceanic and Atmospheric Administration (which houses the NWS) — doesn't think the name "red flag warning" should change, since it's very well-established, particularly out west. But she does think the process could be improved.

The NWS has long been working on a "hazard simplification" effort that would narrow down the numbers of watches and warnings to help the public understand them better, she explains.

She says there have been concerns about "over-issuance" in some parts of the U.S., with parts of the West seeing red flag warnings on a daily basis during very dry summers, which has sparked efforts to revamp the system.

Wall is among the experts talking with the NWS about possible solutions, and they advocate using a severity system for red flag warnings in which the risk would either be labeled as moderate or, in the case of the most extreme conditions, very high severity.

She says as important as it is to improve communication and take precautions, she thinks, "really, where we're going ultimately is with fire-adapted communities" and creating communities that are wildfire-resistant.

"I kind of feel like if you keep things relatively simple, you'll do a better job of catching peoples' attention," Wall says. "But in really wildfire-prone areas, it's just the way of life now. You have to be paying attention and you have to be prepared."