Flash Floods Kill 3 in Colorado; Dangerous 93L Developing in Gulf of Mexico

By: Dr. Jeff Masters , 3:06 PM GMT on September 12, 2013

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Devastating flash floods swept though numerous canyons along the Front Range of Colorado's Rocky Mountains Wednesday night and Thursday morning, washing out roads, collapsing houses, and killing at least two people. The floods were triggered by widespread torrential rains of 4 - 6" that fell in less than twelve hours, thanks to a flow of extremely moist air from the southeast that pushed up against the mountains. These sort of upslope rain events are so-named because as the air flows uphill, it expands and cools, forcing the moisture in it to fall as rain. Balloon soundings from Denver last night and this morning recorded the highest levels of September moisture on record for the station. The total precipitable water (PW), which is how much water would fall at the ground if the entire amount of water vapor through the depth of the atmosphere was condensed, was 1.33" at 12Z (8 am EDT) on September 12, and 1.31" at 00Z September 12. The previous September record was 1.23", set on September 10, 1980. Balloon soundings began in 1948. Wednesday night's rainfall was heaviest near Boulder, Colorado, where a flash flood watch continues through Thursday evening. Though rainfall amounts today are not expected to be as great as on Wednesday, the soils are saturated, and additional flash flooding will occur today as an upper-level low centered over the southern Great Basin continues to pull a moist southeasterly surface flow of air across Eastern Colorado. A map of Boulder flood zones and detailed history of previous floods in the area may be found here.


Figure 1. Flooding in Boulder, Colorado on Wednesday evening, September 11, 2013. Photo posted by brandish on Instagram @photogjake.


Figure 2. Radar-estimated rainfall for the Colorado's Front Range from the September 11 - 12 flash flood event. Rainfall amounts of 6 - 8" (dark rad colors) were indicated near Boulder (circle with a "+" symbol), and confirmed by rain gauge measurements.


Video 1. Flooding in Boulder, Colorado at 36th and Colorado Street on Wednesday night, September 11, 2013.

Dangerous 93L developing in the Gulf of Mexico
A low pressure system (Invest 93L) over the Southwestern Gulf of Mexico's Bay of Campeche is generating heavy rains over the Yucatan Peninsula and adjacent waters as it moves west-northwest at about 5 mph. Radar loops from Mexico show that 93L has a pronounced rotation and is developing low-level spiral bands, and there is a strong possibility that the Air Force hurricane hunter plane scheduled to investigate 93L Thursday afternoon will find that a tropical depression has formed. Satellite loops show only a modest area of heavy thunderstorms, but these are steadily growing in intensity and areal coverage. The atmosphere is unusually moist, ocean temperatures are a very warm 29 - 29.5°C (84 - 85°F), and wind shear is a moderate 10 - 15 knots. These favorable conditions for development are expected to continue through Monday, according to the latest SHIPS model forecast. The computer models predict a landfall location along the Mexican coast between Veracruz and a location a few hundred miles south of the Texas/Mexico border by early next week. The storm is expected to maintain a forward speed of about 5 mph during the coming five days, and this slow motion will potentially allow 93L enough time to intensify into a hurricane before landfall. The high levels of moisture and slow motion of 93L make it a very dangerous rainfall threat, and I expect rainfall amounts of 5 - 10 inches will affect portions of the Mexican coast between Veracruz and Brownsville, Texas over the next five days. An added danger is the presence of tropical disturbance 90E in the Eastern Pacific Ocean, on the other side of Mexico. If 93L intensifies sufficiently, it could draw in the moisture from 90E across Southern Mexico, resulting in torrential rains on both the Pacific and Atlantic sides of Southern Mexico. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 2-day odds of development of 60% and 5-day odds of 80%.


Figure 3. Latest satellite image of Tropical Depression Ten.

Humberto peaks in intensity
Hurricane Humberto is headed northwards over the far Eastern Atlantic, and has likely peaked in strength, with 85 mph winds. Humberto is listed in NHC's preliminary Best-Track data repository as having achieved hurricane strength at 8 am EDT on September 11, which would tie it with Hurricane Gustav of 2002 for latest appearance of the season's first hurricane since 1941. Satellite loops show that Humberto is well-organized hurricane with a distinct eye, but the storm has moved over waters cooler than 26°C, and wind shear has risen to 20 knots, which will likely cause weakening over the next few days. Humberto is not expected to be a threat to any land areas.

Gabrielle heads towards Canada
Tropical Storm Gabrielle is headed northwards to Canada after bringing 40 mph winds and just over an inch of rain to Bermuda on Tuesday night. Satellite loops show that wind shear has ripped up Gabrielle, leaving the storm with almost no heavy thunderstorms, and exposing the low level circulation to view. Wind shear is expected to rise to an extremely high 45 - 70 knots on Friday as Gabrielle encounters a trough of low pressure, which will likely destroy the storm. Gabrielle's remnants will likely bring heavy rain to the Canadian Maritime Provinces on Friday and Saturday.

Jeff Masters

After the Rain (mtnwoman67)
Lots of rain in Colorado for weeks. Last evening's setting sun gave us a great show east of us.
After the Rain

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@WCL_Shawn 3m
In phone interview with The Weather Channel Boulder Emergency Mgmt reports huge mudslides 4ft deep & 400 ft long moving down canyon #COwx
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Quoting 1446. KoritheMan:


Stormchaser asked if 10L was Texas's last chance to get a cyclone for this year, so I highlighted a possibility that the GFS has been consistent with.

Never said the track or pattern of such a long-range was forecast was definite, though. Far from.

If you read back you will notice that I did not quote Stormchaser121.
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Quoting 1445. Stormchaser121:

Can you post the ensembles?


Link
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Quoting 1444. TropicalAnalystwx13:

No. Why would we be discussing the track of a storm exclusively on the GFS over 10 days out?


Stormchaser asked if 10L was Texas's last chance to get a cyclone for this year, so I highlighted a possibility that the GFS has been consistent with.

Never said the track or pattern of such a long-range was forecast was definite, though. Far from.
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Quoting 1431. KoritheMan:


Of the system the ensembles are seeing?

I beg to differ.

Can you post the ensembles?
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Quoting 1431. KoritheMan:


Of the system the ensembles are seeing?

I beg to differ.

No. Why would we be discussing the track of a storm exclusively on the GFS over 10 days out?
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Quoting 1438. LAbonbon:
Boulder County Sheriff and Fire Live Audio Feed

Patrap & Mixon have posted this a few times today.


From the feed: Power lost in Nederland, where I think MrMixon lives (can anyone confirm?), so we may not be hearing from him even after he rests. Hope all is well w/ him.
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Quoting 1436. bappit:
TA13 works in prophet mode.


Pfft. Yeah right. :P
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Much of the same this evening, although not quite as much deep-layer moisture.

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Quoting 1434. moonlightcowboy:



What are you listening to?
Boulder County Sheriff and Fire Live Audio Feed

Patrap & Mixon have posted this a few times today.
Member Since: June 26, 2013 Posts: 0 Comments: 1817
For those curios, here is the sounding analysis from along the front range this morning when the rain may have been at its worst.

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1436. bappit
TA13 works in prophet mode.
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1435. FWBRuss
Quoting 1429. MrMixon:
We're getting some brownouts here. I'm going to grab a little food and try to rest. Wouldn't be surprised to lose power at any point. It certainly will be interesting to see what things look like around the area tomorrow morning... Hopefully we can make it through the rest of this without losing any more lives.

Take care and God speed. Thanks for all the info! Food and rest is good.

Boulder has set a record for its wettest 24-hour period. Ever. Prior to Wednesday, the single wettest day on record was July 31, 1919, when 4.80 inches of rain were recorded.
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Quoting 1421. LAbonbon:


Are you listening to the sheriff/fire audio feed? It's never-ending...I can't make myself turn it off. Waiting to hear about the rescuers who are cut off, who are waiting on the National Guard, who themselves are stuck. The dispatchers, though, I don't know how they keep it all straight. One of them has been on literally all day and tonight.



What are you listening to?
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Quoting 1430. JLPR2:


I learn something new in here everyday.


I learn more interesting things here than I do in school.
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Quoting 1428. TropicalAnalystwx13:

The pattern does not support a USA Gulf Coast strike.


I should press you for proof instead of taking your word as gospel, but I'm going to bed, so...yeah.

Good night guys. And girls.
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Quoting 1428. TropicalAnalystwx13:

The pattern does not support a USA Gulf Coast strike.


Of the system the ensembles are seeing?

I beg to differ.
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1430. JLPR2
Quoting 1422. KoritheMan:


It's not a surprise at all. When a system is in close proximity to a trough, the natural result will be diffluence; concurrent with shear, but diffluence nonetheless.


I learn something new in here everyday.
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1429. MrMixon
We're getting some brownouts here. I'm going to grab a little food and try to rest. Wouldn't be surprised to lose power at any point. It certainly will be interesting to see what things look like around the area tomorrow morning... Hopefully we can make it through the rest of this without losing any more lives.

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Quoting 1426. scott39:
We will get a hurricane strike on the central/N gulf coast.

The pattern does not support a USA Gulf Coast strike.
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Quoting 1423. Astrometeor:


Weather Prediction Center?

Thanks 1900 for the link, another bookmark for me.

Yup, formerly called the HPC, or Hydrometeorological Prediction Center. And you bet!
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1426. scott39
We will get a hurricane strike on the central/N gulf coast.
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Quoting 1419. KoritheMan:


What was the reason for that shift?

Kind of slipped under my nose.

Not sure off the top of my head. The change happened this past spring though.
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Quoting 1417. 1900hurricane:

Because that responsibility has been moved to the WPC.

Link


Weather Prediction Center?

Thanks 1900 for the link, another bookmark for me.
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Quoting 1420. JLPR2:


That is true, but I must admit I expected Gabrielle to become a remnant low today, instead it keeps trying to fire off new convection.

But as you said, with no organized persistent convection over the center it should continue to unwind.


It's not a surprise at all. When a system is in close proximity to a trough, the natural result will be diffluence; concurrent with shear, but diffluence nonetheless.
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Quoting 1406. MrMixon:
From my local email list:

Urgent!

An evacuation has been ordered and warning sirens were activated at 10:15 p.m. for all residents along Boulder Creek from the mouth of Boulder Canyon east to Broadway between Marine and Pearl Streets. All residents are warned to go to higher ground immediately due to the potential for flash flooding along the creek.

Residents near Boulder Creek east of Broadway are urged to shelter in place on high ground.

Boulder Creek is currently flowing at approximately 4,900 cubic feet per second; almost double the volume from earlier today. There are mudslides at the mouth of Boulder Canyon 400 feet long and 4 feet deep as the sides of the canyon give way due to the saturation from the days long rain. Boulder County officials are worried that the mud and rock slides will clog Boulder Creek, causing water to collect upstream and then release, causing a sudden surge in water volume downstream.


Are you listening to the sheriff/fire audio feed? It's never-ending...I can't make myself turn it off. Waiting to hear about the rescuers who are cut off, who are waiting on the National Guard, who themselves are stuck. The dispatchers, though, I don't know how they keep it all straight. One of them has been on literally all day and tonight.
Member Since: June 26, 2013 Posts: 0 Comments: 1817
1420. JLPR2
Quoting 1409. KoritheMan:


The bursts of convection we've been getting over the last couple of days have been recurring, but not very organized. The actual circulation is gradually going to spin down, and Gabrielle will probably not strengthen in advance of the trough. Expect absorption into the trough in about 24 hours.


That is true, but I must admit I expected Gabrielle to become a remnant low today, instead it keeps trying to fire off new convection.

But as you said, with no organized persistent convection over the center it should continue to unwind.
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Quoting 1417. 1900hurricane:

Because that responsibility has been moved to the WPC.

Link


What was the reason for that shift?

Kind of slipped under my nose.
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Quoting 1416. Stormchaser121:

This one BETTER NOT GO TO MX.


It'll go where the pattern favors.
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Quoting 1370. Astrometeor:
How come SPC doesn't issue hydrologic discussions more often?

Today's Reports:

Because that responsibility has been moved to the WPC.

Link
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Quoting 1415. KoritheMan:


The GFS ensembles continue to show a pattern conducive to a potential tropical cyclone in the western Caribbean during the 10 day range. As far as I can tell, they haven't pushed back the timing either like they usually do.

This one BETTER NOT GO TO MX.
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Quoting 1412. Stormchaser121:

Well...Just got home from work. Do we have anymore chances this season? Or is this it.


The GFS ensembles continue to show a pattern conducive to a potential tropical cyclone in the western Caribbean during the 10 day range. As far as I can tell, they haven't pushed back the timing either like they usually do.

This would be a situation supported quite well by climatology also.
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Quoting 1411. Astrometeor:


Just when I thought the situation in Colorado couldn't get any stranger and/or dangerous with all of these twists, it does.


Earlier I think MrMixon mentioned they were calling it a 500 yr flood event. Phenomenal. Scary.
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Quoting 1393. MrMixon:
Current Boulder Creek flows far exceed our spring snowmelt peak this year...


Not to mention every other streamflow peak in the gauge's 25 year history.

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Quoting 1409. KoritheMan:


The bursts of convection we've been getting over the last couple of days have been recurring, but not very organized. The actual circulation is gradually going to spin down, and Gabrielle will probably not strengthen in advance of the trough. Expect absorption into the trough in about 24 hours.

Well...Just got home from work. Do we have anymore chances this season? Or is this it.
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Quoting 1408. moonlightcowboy:


Wow! This just keeps getting worse and worse.


Just when I thought the situation in Colorado couldn't get any stranger and/or dangerous with all of these twists, it does.
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Quoting 1403. JLPR2:
Gabrielle refuses to give up.



The bursts of convection we've been getting over the last couple of days have been recurring, but not very organized. The actual circulation is gradually going to spin down, and Gabrielle will probably not strengthen in advance of the trough. Expect absorption into the trough in about 24 hours.
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Quoting 1406. MrMixon:
Urgent!

An evacuation has been ordered and warning sirens were activated at 10:15 p.m. for all residents along Boulder Creek from the mouth of Boulder Canyon east to Broadway between Marine and Pearl Streets. All residents are warned to go to higher ground immediately due to the potential for flash flooding along the creek.

Residents near Boulder Creek east of Broadway are urged to shelter in place on high ground.

Boulder Creek is currently flowing at approximately 4,900 cubic feet per second; almost double the volume from earlier today. There are mudslides at the mouth of Boulder Canyon 400 feet long and 4 feet deep as the sides of the canyon give way due to the saturation from the days long rain. Boulder County officials are worried that the mud and rock slides will clog Boulder Creek, causing water to collect upstream and then release, causing a sudden surge in water volume downstream.


Wow! This just keeps getting worse and worse.
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Quoting 1393. MrMixon:
Current Boulder Creek flows far exceed our spring snowmelt peak this year...



Thanks for all your reporting.
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1406. MrMixon
From my local email list:

Urgent!

An evacuation has been ordered and warning sirens were activated at 10:15 p.m. for all residents along Boulder Creek from the mouth of Boulder Canyon east to Broadway between Marine and Pearl Streets. All residents are warned to go to higher ground immediately due to the potential for flash flooding along the creek.

Residents near Boulder Creek east of Broadway are urged to shelter in place on high ground.

Boulder Creek is currently flowing at approximately 4,900 cubic feet per second; almost double the volume from earlier today. There are mudslides at the mouth of Boulder Canyon 400 feet long and 4 feet deep as the sides of the canyon give way due to the saturation from the days long rain. Boulder County officials are worried that the mud and rock slides will clog Boulder Creek, causing water to collect upstream and then release, causing a sudden surge in water volume downstream.
Member Since: March 26, 2006 Posts: 44 Comments: 1520
Quoting 1398. Astrometeor:


My guess is that after his heart attack, his doctors and nurses would very much appreciate it if he took it easy for some time, and not get caught up in the blog's dramatic life. Rest is one of the best ways to recovery.

Edit: Kori! Don't even hint at the others like that. You gonna make people worry too much.


I can assure you it's nothing to worry about.
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Sirens are sounding in area east of Boulder to warn people of upcoming wave of water.
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1403. JLPR2
Gabrielle refuses to give up.

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Fire devastates NJ boardwalk rebuilt after Hurricane Sandy
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Quoting 1395. bappit:

Scott Lincoln would be the one to answer that, but I'll guess the SPC does not have the expertise.


Thanks bappit, I'll see if I can contact him about it.
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1400. FWBRuss
Quoting 1394. RufusBaker:


why would the blog interfere with his health??
I don't know the answer to that, but I am missing out on haircuts because my barber is being treated for prostate cancer.

On another note, MrMixon has been giving excellent updates all day on the Boulder situation. Would not be surprised to see some of his feedback in Dr. Master's next update.
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Guess who's back? .... LOLLink
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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