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Meteorology of Saturday's Colombian Flood Disaster That Killed 254

By: Jeff Masters and Lee Grenci , 4:07 PM GMT on April 03, 2017

At least 254 people were killed in the in the city of Mocoa (population 40,000) in southwest Colombia near the border of Ecuador early Saturday, when torrential rains triggered a debris flow on a nearby mountain that surged into the town as a huge wall of water carrying tons of mud and debris. The disaster is the fourth deadliest weather-related disaster in Colombia’s recorded history. Reports from Colombia indicate that 130 mm (5.1”) of rain fell during a short period on Friday night and early Saturday morning, with the heaviest of the rain falling in just two hours, between 23:00 Friday, 31 March and 01:00 Saturday, 01 April, 2017. The rains fell on soils that were already wet from unusually heavy rains during March; the Mocoa region received about 50 percent more precipitation than usual during the month of March. The heavy rains of Saturday morning triggered a debris flow down the Taruca ravine on the northwest side of Mocoa, and this landslide, accompanied by floodwaters, poured into the Sangoyaco River and rampaged through the city of Mocoa. According to a USA Today interview with Jonathan Godt, coordinator of the U.S. Geological Survey’s landslide hazards program, “That mixture can move at 35-40 miles an hour, and because it’s so dense it has a lot more momentum and destructive power than water alone.”


Figure 1. Mocao, Colombia after the Saturday, April 1, 2017 flood.  A video from early Saturday morning showed cars and trucks being swept down the streets. Image credit:  Ejército Nacional de Colombia via Facebook.

Contributing causes to the disaster
The fundamental cause of the disaster was that the city of Mocoa was situated in a vulnerable location—in a valley surrounded by steep slopes, close to the Mocoa, Mulato, and Sancoyaco rivers. Deforestation on the surrounding slopes may have contributed to the landslide and flood. President Juan Manuel Santos blamed climate change for triggering the flood, and he has a point—increased evaporation from warming oceans have caused a significant rise in atmospheric water vapor and very heavy rainfall events like the Mocoa event in recent decades. The Mocoa rains were triggered by a very moist flow of air from the tropical Atlantic, where ocean temperatures were near average (see the meteorological analysis below.) The rainy season in Colombia extends from March to mid June, so additional floods and landslides can be expected the next two months.


Figure 2. Aerial view of Mocao, Colombia after the Saturday, April 1, 2017 flood.  Image credit: Cesar Carrion/Colombian Presidential Office via AP.

Colombia’s history of weather disasters
According to EM-DAT, the international disaster database, Colombia’s most expensive and second deadliest weather-related disaster occurred in 2010 - 2011, when almost non-stop heavy rains caused three separate billion-dollar flooding events, killing 418 people. EM-DAT lists one other flood that killed more than 200 people in Colombia: a December 1971 flood in Magdalena and Cauca Valsfive that killed 307. EM-DAT also lists five landslides in Colombia’s history that have killed at least 200 people:

640 killed in Villatina on Sep 27, 1987
300 killed in Quebrada Blanca on June 28, 1974
200 killed in Bogota on June 28, 1973
200 killed on June 21, 1986
200 killed in December 1971

Meteorology of the disaster
Wunderblogger Lee Grenci looked in detail at the meteorology of the disaster, and what follows is his analysis.

Below is the animation of enhanced satellite images from GOES-13 during the period, 0045 UTC to 0715 UTC April 1 (nighttime in Colombia). You can see a mesoscale convective system (MCS) . This may more properly have been called a mesoscale convective complex (MCC), given the symmetry of the cirrus canopy toward the end of the loop--but the duration of the large, circular cirrus canopy did not last very long, however, and must last at least 6 hours to be labeled a MCC. Needless to say, the MCS was slow-moving, if not stationary, for several hours. The cloud-top temperatures at the peak of deep, moist convection were as low as -90 degrees Celsius, indicative of heavy thunderstorms quite capable of producing very heavy rain.


Figure 3. The animation of enhanced infrared images from GOES-13 during the period, 0045 UTC to 0715 UTC on April 1, 2017. Courtesy of Penn State.


Figure 4. A relief map of Colombia, Courtesy of Wikipedia. The disaster occurred in the town of Mocoa, which lies in southwest Colombia in the department of Putumayo at an elevation of nearly 2000 feet.

Given the quasi-stationary nature of the MCS, it’s pretty clear that the initiation of heavy thunderstorms was orographic in nature. Check out (below) the GFS model analysis of 700-mb streamlines (about 10,000 feet) at 00 UTC on April 2. Please note that I’m using 700 mb as a proxy for the lower troposphere, given the high elevations in this region (mountains to the west of Mocoa are as high as 15,000 feet). The analysis shows a strong easterly flow from the tropical Atlantic that moved upslope over the high terrain, paving the way for heavy thunderstorms. The rapid, extreme run-off from the lofty mountains set the stage for devastating flooding and mudslides.


Figure 5. The GFS model analysis of 700-mb streamlines at 00 UTC on April 2, 2017. Courtesy of Penn State.


Figure 6. The GFS model analysis of 850-mb streamlines at 00 UTC on April 2, 2017. Courtesy of Penn State. Lower-level winds come into South America from the tropical Atlantic and Caribbean.

Moisture from the Caribbean, where ocean temperatures were up to 1°C (1.8°F) above average might have played a role in the MCS, but I believe the mountains to the north probably blocked some of this low-level moisture. To support my claim, take a look at the GFS analysis of precipitable water (PWAT, Figure 7). In my opinion, the broad east-to-west band of high PWAT, with an embedded area of 2.5+ inches, was aimed (given the prevailing easterly flow) directly at the location of the MCS.


Figure 7. The GFS model analysis of precipitable water (PWAT expressed in inches) at 00 UTC on April 2, 2017. Larger image. Courtesy of Penn State.

Final blog post in old software system
This post is scheduled to be the final one in the old software system; the new “Category 6” will use the Drupal software package, and commenting will be via the Disqus software package. The current plan is to leave the current blog archive up for two more weeks, after which time a full archive of all the old blogs will be made available, along with the first 500 comments in each post (no graphics or videos posted to the comments will be saved, though.) WU member Patrap figured out that the Internet Archive's “Wayback Machine" has backups of the blogs; for example, one can access old posts by changing the “entrynum=“ portion of the URL below:

https://web.archive.org/web/http://%20/www.wunderground.com/blog/JeffMasters/comment.htm%20l?entrynum=2835

Our FAQ page has more detailed info on how this transition will occur. Blog commenting is not going away! Check back later on Monday for the first "new" Cat 6 post. 

Jeff Masters and Lee Grenci


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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61. CaneFreeCR
7:18 PM GMT on April 03, 2017
Still looking forward to another blog today about the wild weather in the Southeast US. New format, maybe? :-)
Member Since: December 31, 1969 Posts: Comments:
60. KEEPEROFTHEGATE (Mod)
6:56 PM GMT on April 03, 2017
dumping files clearing Cache full shutdown restart
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59. wxsample
6:46 PM GMT on April 03, 2017
The blog has been a good read, always.
It is nice to see controversial subjects broached now and again as we get to see not only the views of the blogger, but also the many sides of the responses.
What I like about the Disques platform is that comments are nested in with the post. No need to quote repeatedly. Now when people are using the blog as their personal chat room, the rest of us can know when they are talking to the world or just a small number of people. I hope many will find it helpful.
I do feel sad for the people who cannot make the transition or like the change. I doubt I will transition, but I will continur to be a daily reader of the blog.
Best of luck to Category 6 and the new set up.
Member Since: December 31, 1969 Posts: Comments:
58. wxsample
6:42 PM GMT on April 03, 2017
The blog has been a good read, always.
It is nice to see controversial subjects broached now and again as we get to see not only the views of the blogger, but also the many sides of the responses.
What I like about the Disques platform is that comments are nested in with the post. No need to quote repeatedly. Now when people are using the blog as their personal chat room, the rest of us can know when they are talking to the world or just a small number of people. I hope many will find it helpful.
I do feel sad for the people who cannot make the transition or like the change. I doubt I will transition, but I will continur to be a daily reader of the blog.
Best of luck to Category 6 and the new set up.
Member Since: December 31, 1969 Posts: Comments:
57. chinookwx
6:25 PM GMT on April 03, 2017

Possibility of snow here in Denver tomorrow. However as with previous systems looks like it'll move too far south for us to get any significant snow. We've had an active pattern lately. A nice change of pace from 70s everyday which caused a drought.
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56. weathermanwannabe
6:22 PM GMT on April 03, 2017
Very strong low and impressive coverage across the entire eastern half of Conus; be careful out there on the Eastern Seaboard:





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55. Xandra
6:16 PM GMT on April 03, 2017
March for Science‏:
@ScienceMarchDC

.@ScienceMarch_NZ joins #GlobalScienceMarch to tackle the local & global challenges facing science in New Zealand: http://marchforsciencenz.org

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54. KEEPEROFTHEGATE (Mod)
6:13 PM GMT on April 03, 2017
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53. KEEPEROFTHEGATE (Mod)
6:11 PM GMT on April 03, 2017
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52. WU_8344942
6:06 PM GMT on April 03, 2017
St. Petersburg/Clearwater Airport is Sitting at 91 Degrees Right Now, likely Record Hot Territory. Breezy too.
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51. Patrap
6:01 PM GMT on April 03, 2017
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50. Patrap
5:59 PM GMT on April 03, 2017
College of DuPage Meteorology
Severe Weather and Flash Flood Warnings
Note: This page will reload every 2 minutes. Warnings are listed with the most recent first.
Click on the station ID to bring up list of recent severe weather statements.
SVR T-STORM WARNING TALLAHASSEE FL - KTAE 154 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 153 PM EDT MON APR 3 2017
TORNADO WARNING     PEACHTREE CITY GA - KFFC 141 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 136 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 132 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 131 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 128 PM EDT MON APR 3 2017
TORNADO WARNING     PEACHTREE CITY GA - KFFC 122 PM EDT MON APR 3 2017
SVR T-STORM WARNING TALLAHASSEE FL - KTAE 122 PM EDT MON APR 3 2017
SVR T-STORM WARNING TALLAHASSEE FL - KTAE 118 PM EDT MON APR 3 2017
TORNADO WARNING     PEACHTREE CITY GA - KFFC 104 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 1259 PM EDT MON APR 3 2017
SVR T-STORM WARNING TALLAHASSEE FL - KTAE 1259 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 1255 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 1253 PM EDT MON APR 3 2017
SVR T-STORM WARNING PEACHTREE CITY GA - KFFC 1127 AM EDT MON APR 3 2017
TORNADO WARNING     PEACHTREE CITY GA - KFFC 1232 PM EDT MON APR 3 2017
TORNADO WARNING     PEACHTREE CITY GA - KFFC 1230 PM EDT MON APR 3 2017
Member Since: December 31, 1969 Posts: Comments:
49. Patrap
5:56 PM GMT on April 03, 2017
Quoting 45. barbamz:


Thanks, Pat, amazing. And yes, everything still there, even though I've lately scrapped all my personal WU-blogs, lol.


The internet, having many layers is a vast network . Everything is usually being compiled in many servers globally. Many encrypted ones too.

They interface along nodes like a Human Brain more and more.

We all have our closets though. Skeletons have a way of sticking around. Finding them is the chore.

Great to see Blue skies and calm winds in Louisiana today.

Im getting too old for dat stuff.

The sweet corn survived intact too.

Winning!


When I get off of this mountain
You know where I want to go
Straight down the Mississippi River
To the Gulf of Mexico
To Lake Charles, Louisiana
Little Bessie, girl that I once knew
And she told me just to come on by
If there's anything she could do'

Up on Wunder Creek she sends me
If I spring a leak she mends me
I don't have to speak she defends me
A blogger's dream if I ever did see one









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48. nash36
5:55 PM GMT on April 03, 2017


Not cool; threat is increasing this afternoon- I suspect TORCONS will increase.
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47. RobertWC
5:53 PM GMT on April 03, 2017
For Colombia, The Rain Bombs of Climate Change Fell in the Dark of Night
As the lower atmosphere becomes warmer, evaporation rates will increase, resulting in an increase in the amount of moisture circulating throughout the troposphere (lower atmosphere). An observed consequence of higher water vapor concentrations is the increased frequency of intense precipitation events… — NASA’s Earth Observatory

Link
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46. nash36
5:52 PM GMT on April 03, 2017
Surface heating not helping to put the kibosh on severe here later. Hopefully, none of these storms become discrete supercells, and if they do, they die out before reaching SE SC.
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45. barbamz
5:48 PM GMT on April 03, 2017
Quoting 43. Patrap:

This is a wunderblog community FLASH TRAFFIC Bookmark ALERT
Saved 15,414 times between November 21, 1996 and April 3, 2017.

Thanks, Pat, amazing. And yes, everything still there, even though I've lately scrapped all my personal WU-blogs, lol.
Member Since: December 31, 1969 Posts: Comments:
44. RitaEvac
5:45 PM GMT on April 03, 2017
Quoting 43. Patrap:

This is a wunderblog community FLASH TRAFFIC Bookmark ALERT




Saved 15,414 times between November 21, 1996 and April 3, 2017.




I don't understand how it take a snapshot of that day and can still click on links....
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43. Patrap
5:40 PM GMT on April 03, 2017
This is a wunderblog community FLASH TRAFFIC Bookmark ALERT




Saved 15,414 times between November 21, 1996 and April 3, 2017.

Member Since: December 31, 1969 Posts: Comments:
42. 3SeaHorses
5:34 PM GMT on April 03, 2017
Quoting 33. Sfloridacat5:

I had been wondering when this would become the main story in the blog. Boom, here it is now.

Also, IBM and The Weather Underground (the company)
really went the extra mile to make sure they separated themselves from the Weather Underground disqus blog community.

"Weather Underground Community Member Blogs - NOT affiliated, associated, authorized, endorsed, or in any way officially connected with Weather Underground of The Weather Company, an IBM Business."

The Weather Underground Community member blogs are in no way connected to Weather Underground.
In other words - good bye and have fun on your own.


please...its a legal issue. just waiting to see what its like...just be thankful Disney didn't buy them:)
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41. KEEPEROFTHEGATE (Mod)
5:28 PM GMT on April 03, 2017
Quoting 37. barbamz:


The expat WU member blog was founded on Disqus some weeks ago by some members (like aquak9) on their own and is, just as it says, not the official one which will show up later today, connected to WU's Category 6 blog!
just peeps trying things just leave us alone stop assuming things I would say myself
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40. Patrap
5:28 PM GMT on April 03, 2017
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39. NNYer
5:27 PM GMT on April 03, 2017
Well, I finally broke down and made a Disqus account. Curious to see how this goes.
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38. KEEPEROFTHEGATE (Mod)
5:27 PM GMT on April 03, 2017
Quoting 33. Sfloridacat5:



no that is not correct the channel you are on is set up by comm members using the name and gave that notice to indicate such

the real wunderground will be still here at wu but using the drupal/disqus commenting platform later today

the channel on disqus is a place to stay in contact with peeps and set up threads and discussions that individuals have interests in like gardening photos weather etc etc etc
Member Since: December 31, 1969 Posts: Comments:
37. barbamz
5:20 PM GMT on April 03, 2017
Quoting 33. Sfloridacat5:


The expat WU member blog was founded on Disqus some weeks ago by some members (like aquak9) on their own and is, just as it says, not the official one which will show up later today, connected to WU's Category 6 blog!
Member Since: December 31, 1969 Posts: Comments:
36. swarfmaster
5:17 PM GMT on April 03, 2017
Any thoughts about the rain predicted for the Sierra next weekend? Looks like a fair amount of rain which could lead to some flooding.
Member Since: December 31, 1969 Posts: Comments:
35. weathermanwannabe
5:12 PM GMT on April 03, 2017
33. Sfloridacat5
1:00 PM EDT on April 03, 2017
That disclaimer is no different that the one you see on newspaper or television news station websites that allow viewers to comment on the news story in a Disqus format...................Standard boilerplate disclaimer that the comments made do not reflect the station views, yada, yada, yada to distance themselves from really offensive comments or statements as well as lies or factual misrepresentations.  No big deal. 
Member Since: December 31, 1969 Posts: Comments:
34. Uragani
5:03 PM GMT on April 03, 2017
Last, before turning into discus:
Member Since: December 31, 1969 Posts: Comments:
33. Sfloridacat5
5:00 PM GMT on April 03, 2017
I had been wondering when this would become the main story in the blog. Boom, here it is now.

Also, IBM and The Weather Underground (the company)
really went the extra mile to make sure they separated themselves from the Weather Underground disqus blog community.

"Weather Underground Community Member Blogs - NOT affiliated, associated, authorized, endorsed, or in any way officially connected with Weather Underground of The Weather Company, an IBM Business."

The Weather Underground Community member blogs are in no way connected to Weather Underground.
In other words - good bye and have fun on your own.
Member Since: December 31, 1969 Posts: Comments:
32. 19N81W
4:57 PM GMT on April 03, 2017


brings tears to our eyes and sweat
Member Since: December 31, 1969 Posts: Comments:
31. 19N81W
4:56 PM GMT on April 03, 2017


not much change here 4 months and counting
Member Since: December 31, 1969 Posts: Comments:
30. 19N81W
4:53 PM GMT on April 03, 2017
Member Since: December 31, 1969 Posts: Comments:
29. aquak9
4:50 PM GMT on April 03, 2017
I'm still here too. Hmmph.
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28. WXGulfBreeze
4:41 PM GMT on April 03, 2017
Quoting 17. PensacolaDoug:

Still here!


Still wet.
Member Since: December 31, 1969 Posts: Comments:
27. weathermanwannabe
4:40 PM GMT on April 03, 2017
Two tornado warnings up at the moment south of Atlanta; about 4-5 warnings up the radar loops this morning, but no preliminaries up yet on the SPC board, but several wind reports across the board with multiple reports of 40-50 mph gusts and trees and power lines down in Alabama and Georgia;

today Filtered Reports Graphic





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26. NNYer
4:33 PM GMT on April 03, 2017
Whole lotta wet coming my way.
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25. JimSpriggs
4:32 PM GMT on April 03, 2017
Hello, It's Me
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24. KEEPEROFTHEGATE (Mod)
4:29 PM GMT on April 03, 2017
Member Since: December 31, 1969 Posts: Comments:
23. KEEPEROFTHEGATE (Mod)
4:29 PM GMT on April 03, 2017
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22. Uragani
4:28 PM GMT on April 03, 2017
Steaming to you live and hotheadedly from Tirana, Albania:

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21. KEEPEROFTHEGATE (Mod)
4:28 PM GMT on April 03, 2017
Member Since: December 31, 1969 Posts: Comments:
20. KEEPEROFTHEGATE (Mod)
4:25 PM GMT on April 03, 2017
Quoting 16. PedleyCA:

The Fun hasn't started yet......
no not yet soon
Member Since: December 31, 1969 Posts: Comments:
19. Greg01
4:24 PM GMT on April 03, 2017
It Lives! Well, for a few hours anyway...
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18. 19N81W
4:22 PM GMT on April 03, 2017
we need that low to drift to the western carib desperately......sorry for those lost
Quoting 14. KEEPEROFTHEGATE:


Member Since: December 31, 1969 Posts: Comments:
17. PensacolaDoug
4:22 PM GMT on April 03, 2017
Still here!
Member Since: December 31, 1969 Posts: Comments:
16. PedleyCA
4:22 PM GMT on April 03, 2017
The Fun hasn't started yet...... Thanks for the updates Dr. M & Lee Grenci....
Member Since: December 31, 1969 Posts: Comments:
15. ChillinInTheKeys
4:22 PM GMT on April 03, 2017
Below the NEXRAD, there used to be a list of the storms noting their speed, cloud top heights, hail etc.
Where does one find this info these days? Thanks!
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14. KEEPEROFTHEGATE (Mod)
4:21 PM GMT on April 03, 2017
Member Since: December 31, 1969 Posts: Comments:
13. KEEPEROFTHEGATE (Mod)
4:19 PM GMT on April 03, 2017
nice update good info thanks

that region has a perpetual low pressure area as well during tropical season low pressure is always down that region of the tropical carb.

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12. barbamz
4:19 PM GMT on April 03, 2017
Well, this was a bit unexpected, but the grim tragedy in Colombia deserves a post without clutter about the new format for sure. Thanks for the update and the explanations.

Colombia starts to bury 262 landslide victims, search continues
by Reuters, Monday, 3 April 2017 15:44 GMT
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11. 19N81W
4:18 PM GMT on April 03, 2017
so we can still post?
Member Since: December 31, 1969 Posts: Comments:

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather