Opinion: Flash Flooding Needs to Be Severe Criteria

I think people are way too critical of National Weather Service official criteria. Some say “Why don’t you issue warnings for 30 mph winds,” while others say, “I will not acknowledge a warning for a storm that is not of that strength!” It goes on and on with the nitpicking, ridiculous suggestions and opinions that aren’t rational, or are just supportive of individual agendas.

My reaction when I see people nitpicking the NWS because they have crazy agendas. h/t giphy

However, there is one place in which I think the severe thunderstorm criteria needs changing, and that is with regards to flash flooding. The current definition of a Severe Thunderstorm is as follow:

1″ diameter or larger hail
58 mph wind gusts or higher
A possible tornado

Obviously, a likely tornado constitutes a Tornado Warning, but it is still a Severe Thunderstorm. I digress from that point to the greater point. Outside of a severe thunderstorm producing a tornado, how big of a danger are the other two pieces of criteria? Yes, they do damage to houses and trees and vehicles. However, 1″ hail won’t kill someone. 58 mph winds by themselves aren’t killers. The trees and powerlines that fall with them are the killers. Tornadoes are killers, but how often? Looking at 30 year averages from the National Weather Service, the stats look like this:

Tornadoes: 70 deaths per year
Lightning: 48 deaths per year
Flooding: 82 deaths per year

The statistics for the past 10 years are similar, but include wind related fatalities:

Tornadoes: 110 deaths per year
Lightning: 31 deaths per year
Wind: 56 deaths per year
Flooding: 84 deaths per year

This is a fairly consistent trend, as well. While wind related deaths aren’t included in the 30 year average because they weren’t recorded as a separate cause of death until 1995, it is likely that those statistics are similar to the 10 year average. And, the 110 number for tornadoes is misleading. 2011 alone had 553 tornado-related deaths, and 158/553 deaths were caused by one tornado. When this year is removed from the 10 year average, the 9 year average drops to 61 tornado related deaths, which is a substantial drop and is better for comparison sake.

Statistics on yearly weather related deaths. The 10 year and 30 year averages are on the bottom of the page. For the tornadoes, I shortened the 10 year average to a 9 year average to remove the highly anomalous 2011 tornadoes. This aided in creating a more accurate comparison. h/t NWS

Flooding is, by and large, considered its own risk all together, and is often grouped as a separate entity. However, these statistics show that it shouldn’t be. Flash flooding is not as well advertised in discussion of severe weather events; if an event is likely to produce severe weather, the severe weather takes precedence over advertising for a flash flooding threat. Last week was a good example. While high amounts of precipitation were forecast multiple days in advance, once we got to the events themselves, the severe weather threats took precedence.

On Wednesday, we had a strong MCS move through the region, clouding over some of the signals for a more significant flooding threat that night (I missed that badly). The NWS in Louisville, one of the best offices in the country, event struggled a bit, but came back with a Flash Flood Watch to give people some lead time. Additionally, we only had a “See Text” outlook from the WPC initially that day, and it was later upgraded to a moderate risk across out region.

The percent of normal rainfall that we received in 10 days across the region. h/t NWS Louisville

The initial flash flood outlook is on the left, and on the right is the one issued later in the evening. h/t WPC

A similar scenario played out just this past Monday. An enhanced risk for severe thunderstorms was issued across Minnesota and parts of the Dakotas, and this is what gained the attention of forecasters. NWS Duluth’s region saw up to 10″ of rainfall, and they only briefly mentioned a flash flooding threat, even after making note of the climatologically high PWAT values across the region. Severe weather clouded over this, and nothing was issued that would provide at least a bit of lead time for the flash flooding threat (i.e a Flash Flood Watch).

I’m not saying this to criticize the National Weather Service, or any office in particular. I love the NWS and will defend them forever, as they have the best meteorologists in the world. I am using this as a point. Unless the event is primarily a flash flood threat, flash flooding threats tend to be overlooked by meteorologists in general.

Flooding is, statistically speaking, of higher threat to life, and likely to property as well. Lets look at average costs of damage from other natural disasters, per NCDC statistics:

Severe storms: $2.2 billion annually
Winter storms: $2.9 billion annually
Flooding: $4.0 billion annually

Additionally, the amount of people living in floodplains is wild. There are 17,000-18,000 communities in the US that are flood-prone, 15% of urban areas are flood-prone, and 10 million households are at risk for flood damage, according to FEMA.

So, flash flooding compares both in threat to life and threat to property. Additionally, flash flooding is often times a product of severe thunderstorms. You can make the argument to me, “Well, Pierce, flash flooding can be produced by non-severe thunderstorms.” True, very true. Hail is also produced by non-severe thunderstorms, wind damage can be produced by non-severe thunderstorms, and thunderstorms can produce tornadoes and not have hail or 58 mph winds within the main downdraft of the storm.

The point is that 1″ hail and winds of 58 mph or greater are a product of severe thunderstorms, just as flash flooding can be. Now, to be officially classified as a severe thunderstorm, it needs to meet the criteria above; but often times, severe thunderstorm warnings aren’t verified. And, as we have seen above, flash flooding is not only comparable, but poses a greater threat to life and property than wind, hail and tornadoes do individually. So why isn’t it listed under severe thunderstorm criteria?

We don’t have to have to issue severe thunderstorm warnings for flash flooding situations; although, that may be worth considering if it emphasizes the threat to life and property of flash flooding. A severe thunderstorm watch isn’t issued when the threat for tornadoes is high; a tornado watch is. A severe thunderstorm warning isn’t issued if a tornado has been spotted; a tornado warning is. Similarly, we can continue issuing Flash Flood Watches/Warnings to eliminate oversimplification. However, just as tornadoes are listed under what can classify a thunderstorm as severe, so should a flash flood. It is statistically apparent that they are, at the very least, as severe as tornadoes, 1″ hail and 58 mph winds. We should classify them as such.