Impact-Based FFWs a step, but not a solution

By: Dr. Josh Eachus

FLASH FLOOD WARNING! (But, you don’t have to worry about this one)

Within the next few weeks, the National Weather Service (NWS) will be implementing Impact-Based Flash Flood Warnings. The goals are to provide easily readable information and to improve public response. However, like most weather messaging, some significant efforts will be needed to avert confusion.

Prior to Impact-Based Flash Flood Warnings (FFW), all FFWs trigger Wireless Emergency Alerts (WEA) to mobile devices. With over 12,000 FFWs issued each year, public perception is that is that the NWS over-warns on FFWs. State and federal officials report many complaints about WEAs that result in minimal impact.

In the Impact-Based format, FFWs will contain bullet points of clearer information about the flash flood, including the source of the information and a description of the impacts along with a “damage threat” tag. Perhaps most importantly, these damage threat tags will mean that only FFWs tagged “considerable” or “catastrophic” will trigger a WEA. Problem solved, right? Not so fast…




On one hand, this effort should be applauded for attacking perceived false alarms and potential cry-wolf syndrome. However, the change is likely to create substantial public confusion regarding the FFW product. Understand that while the number of WEAs will indeed be reduced, there will not be any changes (aside from normal annual variance) to the number of FFWs issued.

This tasks communicators with differentiating between different levels of FFWs. Why issue a FFW if “considerable” or “catastrophic” impact is not expected? What defines a FFW that does not need a WEA?

Certainly, there are hydrological criteria that constitute FFW issuance specific to weather forecast areas around the country. From a meteorological standpoint, the criteria make sense. From a communication standpoint, criteria routinely create vast weather communication challenges. Criteria led to the infamous communication gaffes in Hurricane Sandy and partially fueled the tremendous HAZSIMP (hazard simplification) efforts of the last several years.

The hydrological criteria that determine a FFW vary regionally. In flood prone areas of the Gulf South, there are dozens of annual instances of street or poor drainage flooding. These situations arise from stationary summer thunderstorms that dump a fast two to three inches of rain. There are certain low-lying areas that always hold water. Even in these cases, it is often standing water that is ankle to knee deep, certainly capable of stalling a vehicle, but unlikely to kill. Rarely are there rushing torrents of water that sweep vehicles and people away as many may envision in a flash flood. Flood Advisories (FA) are often adequate to remind people not to drive across flooded roads. In northern areas with extensive topography, the hydrological response is more rapid and drastic. Much lower rain amounts can lead to far greater water inundation and streams can quickly become rushing rivers. Incongruence in hydrological criteria for a FFW is a fine, even necessary, issue to maintain within the meteorological community. However, for products purposed to alert the public, messages are ideally clear and concise, with minimal room or need for interpretation. The criteria for flooding are simple, and right in front of us. The flooding is either life threatening, or it is not. In an Impact-Based system, the threat to life and property is the impact.

A stepped structure such as FLOOD ADVISORY –> FLASH FLOOD WARNING –> FLASH FLOOD EMERGENCY (accompanied by WEA) would be a prudent solution. Unfortunately, the forthcoming change is just one degree off from this idea, with a two-tiered FFW versus a separate and more significant product. Instead of being more liberal with FAs, more conservative with FFWs, and reserving the Flash Flood Emergency for life threatening scenarios, we are just creating a product within a product.

How are we to communicate a FFW that is “considerable” or “catastrophic” versus one that is not? Why are two different situations triggering the same product? Why keep the FA product for non-life threatening flooding if there is some level of FFW that is also not life threatening? While meteorologists may be able answers these questions (to an extent), can Joe and Jane Public?

Assume somebody receives a WEA for a FFW and turns to their preferred source for more information. The source explains the life-threatening nature of the situation. At another time in the future, that person also hears about a FFW for their favorite source but does not receive a WEA. Without significant attention to the source message, which is not often given under duress, how is that person to parse the difference between this FFW and the last? Would they not assume this is also a life threatening situation, respond accordingly, and once again be victim of an overabundance of FFWs? Perhaps the opposite could be true. A person will be affected by numerous FFWs before one actually warrants a WEA. Would they then ignore the situation and then be in serious danger?




To be clear, the NWS should be lauded for ongoing efforts to improve weather communication. Flooding is routinely the most deadly hazard, but carries a much lower fear factor than hurricanes or tornadoes. This Impact-Based Warnings system is the right way to go. Reducing WEAs and false alarms are necessary steps to combat public complacency and to build trust. HAZSIMP has led to many great improvements in the NWS warning regimen. However, over-simplification can be just as dangerous as over-complication if not done sensibly. This enterprise has to be careful that a growing need for fewer alerts and better communication does not turn the weather warning system into a hazard of simplification.

3 thoughts on “Impact-Based FFWs a step, but not a solution

  1. I sometimes wonder how much “the public” sees or reads those tags, and of those, how many think much about them. They appear on our TV station’s platforms (web, app, on-air crawl) since those are simply displaying the warning text. Personally, I think the damage tags are less useful than the others (source, wind/hail magnitude and tor possible for SVR, and now the causative event for FFW).

    Liked by 2 people

    • They could (should) be critical for EMs / partners / and probably even the public, but as long as the NWS “hides” them at the bottom it won’t happen. It’s more important to get out the CTAs for NOAA Weather Radio than to put the important stuff off the top 😦


  2. The fix that I had met with NWS about was to remove the “normal” FFW from WEA, and add FFW Emeregncy to WEA. The tiers are meaningless so I hope people don’t get caught up in that. Unfortunately so many offices treat the regular FFW as “Your normal route to the shopping mall might have some water up to the curbs” so I think this was the easiest fix to let those offices keep issuing those.

    Liked by 1 person

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