at 2:14 PM by Pierce Larkin

What Happened in Louisiana Last Week?

Natural disasters don’t happen every day, but they aren’t too uncommon. You’ll get tornadoes that strike towns, and produce terrible damage. Flash flooding effects a small town, much like the event in Maryland a few weeks ago. A snow event will effect a portion of the country, but not significantly, etc. But events like last week’s flooding event in Louisiana do not occur very often.

There was a 31″ rainfall maximum across a 7 day timespan, but really, most of that occurred during a 3-Day timespan. The rain began falling early on August 11th, and continued falling through the 13th. Since, the state has seen continued heavy rainfall and thunderstorms and additional flooding.  

What went into this, meteorologically, though?

The Meteorology

Well, this is both complex, and simple. A trough of low pressure began to form at the surface in response to a weak trough in the low and mid levels of the atmosphere. This system formed along the Gulf of Mexico, and because of this, it was able to draw from, and surround itself with, an entirely tropical airmass. The airmass surrounding the Gulf Low was very tropical in nature, and the moisture in the atmosphere associated with it was historically anomalous.

The area in the blue circle has PWAT values at least 3 standard deviations above normal (aka a historically moist air mass). h/t cms.met.psu.edu
The area in the blue circle has PWAT values at least 3 standard deviations above normal (aka a historically moist air mass). h/t cms.met.psu.edu
The SPC PWAT climatology for Jackson, Mississippi. 12z August 12 is selected, and the record for that day is boxed in black. h/t SPC
The SPC PWAT climatology for Jackson, Mississippi. 12z August 12th is selected, and the record for that day is boxed in black. h/t SPC

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The system was a warm-core system, which is a feature that distinctly separates tropical systems from mid-latitude systems. This was easily observed through the highly anomalous moisture content throughout the atmosphere. There were a couple days in a row in which nearly the entire column was near saturation during a sounding at one of the upper air sites along the gulf coast, which is incredibly rare outside of tropical storms or hurricanes.

This is as close to being a tropical sounding as it gets. h/t SPC
This is as close to being a tropical sounding as it gets. h/t SPC

This system was described as, and compared to, a weakening tropical depression that just sat and spun across the Gulf Coast for multiple days. And it was like that. The surface low/trough, 850 mb low and 700 mb low were all stacked as they slowly moved westward along, and just inland from the Gulf. Because the system was surrounded by a historically moist airmass, this set the Gulf Coast up for a weather event that could be potentially disastrous.

The surface pressure at 00z on August 12th. h/t SPC
The surface pressure at 00z on August 12th. h/t SPC
850 mb heights at 00z on August 12th. h/t SPC
850 mb heights at 00z on August 12th. h/t SPC
The 700 mb heights at 00z on August 12th. h/t SPC
The 700 mb heights at 00z on August 12th. h/t SPC

And it was. With a stacked tropical low like that, the forcing was consistently there, and thunderstorms were nearly always concentrated just south of the surface trough. It rained, and rained, and rained, and then it rained some more.

A sample of the radar data from the afternoon of August 11th through the afternoon of August 12th. h/t SPC
A sample of the radar data from the afternoon of August 11th through the afternoon of August 12th. h/t UCAR Archive

The Forecast and Event

The rainfall totals were unbelievable along the Gulf Coastline. And you know what? This event was excellently forecast, too. The WPC forecast this days in advance, and issued accurate and adequate products for this region, giving plenty of time to prepare and have a safety plan in place.

The local National Weather Service office in New Orleans gave citizens plenty of time to plan accordingly, prepare their belongings, and prepare for possible action if flood waters were to rise. Lead times on flood watches were at least 3 days across some of the affected region.

The WPC and NWS office in New Orleans became a great tandem during the event, as well. The WPC had accurately issued good QPF forecasts several days in advance for this event, had fantastic mesoscale discussions, and highlighted the level of the flooding threat through their issuance of High Risks for Flash Flooding.

wpc_7day_laflood
The 7 day rainfall forecast from the WPC on August 9th did an excellent job of pinpointing where the heaviest rain might fall. h/t WPC

The products even included some harsh wording, and highlighted the risk of life-threatening situations to local NWS offices and local media in Louisiana. In Mesoscale Discussion 550, issued on August 12th, they stated, “…LIFE-THREATENING RUNOFF AND/OR FLASH FLOODING IS EXPECTED WITH SUCH INTENSE RAINFALL RATES AND STORM TOTALS GOING THROUGH THE MORNING HOURS.”

The Mesoscale Discussion issued by the WPC on August 12th highlighting the high risk for life-threatening flash flooding. h/t WPC
The Mesoscale Discussion issued by the WPC on August 12th highlighting the high risk for life-threatening flash flooding. h/t WPC

They issued High Risks for Flash Flooding two days in a row for basically the same region, highlighting the level of severity they were expecting over the state of Louisiana.

The High Risk for flash flooding issued on August 12th by the WPC. h/t WPC
The High Risk for flash flooding issued on August 12th by the WPC. h/t WPC
The High Risk for flash flooding issued by the WPC on August 13th. h/t WPC
The High Risk for flash flooding issued by the WPC on August 13th. h/t WPC

The National Weather Service in New Orleans did their part excellently as well. They issued Flash Flood Watches multiple days in advance, but during the event they seemed to do an excellent job of conveying the threat by issuing multiple Flash Flood Emergencies across the region.

These even contained heavy wording within them. The NWS New Orleans state in one of their Flash Flood Emergencies, “…MOVE TO HIGHER GROUND NOW. THIS IS AN EXTREMELY DANGEROUS AND LIFE-THREATENING SITUATION. DO NOT ATTEMPT TO TRAVEL UNLESS YOU ARE FLEEING AN AREA SUBJECT TO FLOODING OR UNDER AN EVACUATION ORDER.” They did absolutely everything they could in their power to convey the significance of this event to the public.

The disaster here didn’t occur because of a lack of NWS forecasting. The event as a whole occurred because this was a historically anomalous meteorological scenario, and was one that was bound to be destructive. However, the NWS did everything they could to prevent this from becoming a social disaster in which lives were lost and property was unsalvageable. Unfortunately, that goal wasn’t accomplished.

The Aftermath

This is likely to be one of the worst, if not the worst, large scale flooding disaster not caused by a tropical system in US history. Entire neighborhoods and towns saw their homes damaged or destroyed. Families were displaced, and the meteorology behind this system will be studied for years to come.

I don’t want to say this because April 27th, 2011 was one of the most anomalous weather events I have ever witnessed in my life, but this may end up being the April 27th of flash flooding. I’ll get to that in a second, though.

This event is likely the worst natural disaster since Sandy in 2012, and is one of the worst flooding events in years. Some estimate that up to 40,000 homes have been damaged, and 30,000 people have been displaced. Additionally, 13 people have died in direct relation to the floods over the past week. Dozens of records along rivers in Louisiana have been broken over the past week, and much of those rivers rose very quickly between the 11th and 12th last week.

Look at how quickly the water rose on this river in Louisiana. h/t NWS New Orleans
Look at how quickly the water rose on this river in Louisiana. h/t NWS New Orleans

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This River beat its old record by a lot, and likely kept rising even further. h/t NWS New Orleans
This River beat its old record by a lot, and likely kept rising even further. h/t NWS New Orleans

And then there are the actual pictures of how areas in Louisiana were affected by these flood waters. NOAA got satellite images of some affected towns in Louisiana, and it is heartbreaking to see the level of destruction that will likely be seen once the waters subside.

The flooding in Abbeville, Louisiana. h/t NOAA
The flooding in Abbeville, Louisiana. h/t NOAA
The flooding in Denham Springs, Louisiana. h/t NOAA
The flooding in Denham Springs, Louisiana. h/t NOAA
The flooding in Port Vincent, Louisiana. h/t SPC
The flooding in Port Vincent, Louisiana. h/t SPC

Then there are images from people on the ground and in the flood. Some of these are just wild.

The aftermath of this event likely won’t be know for quite some time. Flood waters don’t tend to subside quickly, and parts the region continue to be hit by heavy rainfall. This will make the clean up time elongate, and will make it difficult to get a grasp on the full brunt of this event anytime soon.

Flash Flooding Needs a Rebrand

This event has shed light on a new area of meteorology in which meteorologists struggle with communication: flash flooding. As I mentioned above, the National Weather Service in New Orleans and the Weather Prediction Center did their part in all of this. They issued products with plenty of lead time, emphasized risks within these products, and put it out there for the local news media and citizens to get ahold of.

So, how did we get to this point? This was the same question asked 5 years ago on a Thursday morning. The meteorological community was waking to find out that the tornadoes the day before had obliterated communities and killed well over 300 people. In 2011. In the modern age of meteorology, a catastrophe on a level which many couldn’t comprehend, had occurred.

Tornado tracks and related deaths on April 27th, 2011. h/t SPC
Tornado tracks and related deaths on April 27th, 2011. h/t SPC

Local NWS offices began red flagging this event over a week away, and had begun to discuss the potential for a major tornado outbreak several days before. The Storm Prediction Center issued a High Risk, and had a risk area outlined 5 days in advance. What happened? Well, we have since discovered that we are terrible at communicating risk to the public. False alarm rates were way too high, and thus, people had a difficult time believing that the event was going to unfold. To be very honest, it sucked, and it still sucks.

While this rainfall event likely won’t be on the same level in terms of death toll, everything leading up to the event was perfect, just like April 27th. When the event happened, everything fell apart, just like April 27th. You may see the death toll and think, “Well, that is horrible, but 13 isn’t even in the same ballpark as 316.” You are correct about that. However, that is a misleading statistic.

Do you see what I see in those tweets? Rows and rows of cars driving through flooded roadways, and many look to be stuck where they are. This is something that is much easier to quantify and examine than the death toll in this case. People were putting themselves in danger in this scenario. In a tornado outbreak, there are only a certain amount of things that you can do to prepare if a tornado is about to strike your house. However in a flood, much of the safety is in your hands. Avoiding flooded roadways, and seeking higher ground are the essentials in avoided flood related deaths. That seems easier said than done, especially when people haven’t listened to several days of watches and warnings that this event was going to be in the severe to extreme category of flooding events.

So, what can we do? Earlier this summer, I discussed why flash flooding needs to become a part of severe thunderstorm criteria. This event proves it. Flash flooding needs to be rebranded, bottom line. It needs a rebrand. The lack of concern towards flash flood watches, warnings, etc. is obvious, and is very well noted with this event. The public obviously does not see this meteorological anomaly as a threat.

h/t http://tadd.weather.gov/
h/t http://tadd.weather.gov/

Every time there is a big flash flooding or flooding event, we see plenty of stories about high water rescues. These are largely dominated by people driving through a flooded roadway, and getting stuck. This should not happen. Just like the way we pride ourselves with preparing people with the essential knowledge, information and resources necessary to survive a tornado or severe thunderstorm, the meteorological community absolutely has to do the same for flooding and flash flooding. That is the bottom line.

Along these lines falls these vast amount of flooding products issued by the NWS. This is one of the biggest issue with the way the NWS does things. There are:

  1. Flash Flood Watch
  2. Flash Flood Warning
  3. Flood Advisory
  4. Flood warning
  5. Coastal/Lakeshore Hazardous Message
  6. Hydrologic Outlook
  7. Flash Flood Statement
  8. Flood Statement

I love the NWS, and even I admit that the amount of products they issue is way too large. Why not shrink that down to:

  1. Flash Flood Watch
  2. Flash Flood warning
  3. Flood warning

How hard would that be to do? The other stuff isn’t necessary, especially for the public. In addition to that, why don’t we treat Flash Flood Watches like we do Tornado and Severe Thunderstorm watches? I used to think that was a ridiculous idea (which is why I didn’t propose it back in July). However, the more and more I think about it, the more I love the idea. The majority of Flash Flooding events aren’t going to occur continuously over a long period of time. Yes, you get events like this one, but even that came in bouts. What good does it do to issued a Flash Flood watch on a Tuesday and a Wednesday when rain isn’t even falling?

This is similar to the warning issue that the weather world ran into in 2011. In theory, the April 27th event should have given everyone plenty of time to get to an adequate shelter. Lead times that day were in the mid and upper 20 minute range. However, there is a sweet spot. The study linked is about tornadoes, but the general idea remains. If the lead time for a meteorological event is too large, it creates a mindset of doubt after a bit, and makes people less likely to seek shelter or protection from the event.

The same idea remains for Flash Flooding. Watches are issued when, “Conditions are ripe” for tornadoes or severe weather. Warnings are issued when it has, “Been observed or is indicated by radar to be occurring.” So why is this not applied to flash flooding? Flash flooding is deadlier and just as costly as tornadoes and severe weather, so why isn’t it treated that way by meteorologists? Issuing a Flash Flood Watch on a sunny, Tuesday afternoon for an event 3-4 days away doesn’t make much sense, and likely just pushes people into apathy towards the event as a whole. A PDS Flash Flood Watch could even be introduced for the more significant of events. Just something that would help to alleviate the threat of apathy creeping into the public’s mind.

I firmly believe that the WPC should have the jurisdiction to issue Flash Flood Watches. Their meteorologists are trained in hydrometeorology, and they specialize in products around that side of meteorology. If Flash Flood Watches were to be treated similarly to tornado or severe thunderstorm watches, I believe that this would be the key to a rebrand of Flash Flooding as a legitimate threat within the meteorological community. We can keep treating flash flooding like it is a secondary threat. However, until we acknowledge it is a major threat with many strong thunderstorms, we will keep seeing an uneducated and unprepared public.