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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Firehose...

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Quoting 90. StormTrackerScott:


Especially once 93L gets in trained into the monsoon flow. That could really magnify things in New Mexico & Colorado.



I didn't mention that, but that's just another piece of the puzzle. It's really incredible. It could be quite historic for that area.
Member Since: January 1, 2008 Posts: 0 Comments: 3370
Here comes the East Coast Seabreeze.

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95. wpb
RECON on the way down to boc
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Quoting 85. rmbjoe1954:


And that would be a good thing for our Mexican neighbors.


yep. any chance this have of making it to hurricane status decreasing by the hour imo
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recon is up and out....will be anxious to see what they find
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Quoting 80. GatorWX:
Not a good scenario.






Especially once 93L gets in trained into the monsoon flow. That could really magnify things in New Mexico & Colorado.

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I'm a little late but Good Morning everyone :) Unfortunately didn't have time to get the blog coffee and donuts this morning, please accept my apologies.
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the recon is up


Link
Member Since: May 21, 2006 Posts: 5091 Comments: 115256
You all have a great day!
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Quoting 77. DavidHOUTX:


Looks like it is trying hard to get into Mehico in the next day or 2 also


Oooooooool' Mehhhhhhhico
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Quoting 78. HurricaneCamille:
it racing for mexico way too fast.

look like it not gonna become powerful it moving too fast.



And that would be a good thing for our Mexican neighbors.
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latest gfs has 93 lingering just offshore northern mexico maybe.making it inland
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I am hoping that after 93L hits Mexico that it turns north and heads into central Texas. I am now living in Southeast Texas and we really need the rain. So if 93L can come here I would be very happy
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Not a good scenario.




Member Since: January 1, 2008 Posts: 0 Comments: 3370
Quoting 66. VR46L:


Please God give Caribboy the rain he desires !( he gets very grumpy otherwize..)


Lol I would rather say "the rain he deserves" XD XD
Member Since: October 6, 2007 Posts: 0 Comments: 6228
it racing for mexico way too fast.

look like it not gonna become powerful it moving too fast.

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Quoting 46. GetReal:




It is trying hard.


Looks like it is trying hard to get into Mehico in the next day or 2 also
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Quoting 39. SouthernIllinois:

Yup. There ya go.


In Sooo Cal in summer it seems we need PWS OF 2.0 and higher to get thunderstorms to develop with daytime heating the trigger.

As far as Orographics are concerned...I live in the mountains( such as they are in San Diego County) and for winter storms( cold fronts) we usually get southerly flow or southwesterly flow....on "average" the mountains will receive between 2-3 times more rainfall than along the coastal plain/beach areas. San Diego yearly rainfall average is like 10.75" and out by my location 40 miles inland 25" per year.
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Quoting 71. cmckla:
Looks like Dr M is in agreeance with what my local meterologists have been saying all week regarding 93l's track. Why can't some in here just stop saying others are wrong and go with the current conditions and current steering patterns.

Everyone knows getting it right 7+ days out is impossible. What I do know is if you see model tracks clustered together its a pretty locked in path. Like we have here with 93l. On the otherhand, if you see some clustered and some not, then other paths are plausible.


Current is only Current....things change!
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Quoting 67. AussieStorm:



Goodnight



OMG!!!!!!!!!!!!!!
Member Since: October 6, 2007 Posts: 0 Comments: 6228
Hope 93L don't make a lot of destruction in Mexico or Texas.Wishing for the best.I may say that this situation reminds me of what happen in Central America in 1998 and 1974 that if Ingrid becomes a big hurricane it might pulll the moisture of the pacific like Mitch and Fifi.hope the people in Mexico is being advice about this systems and thanks for The informative blog Dr.Masters
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Quoting 61. ILwthrfan:


ULL could rip it apart too, it certainly isn't helping it at the moment.


LOL!
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Looks like Dr M is in agreeance with what my local meterologists have been saying all week regarding 93l's track. Why can't some in here just stop saying others are wrong and go with the current conditions and current steering patterns.

Everyone knows getting it right 7+ days out is impossible. What I do know is if you see model tracks clustered together its a pretty locked in path. Like we have here with 93l. On the otherhand, if you see some clustered and some not, then other paths are plausible.
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Amazing what's happening in CO.



Imagine it's going to get a lot worse before it gets better.
Member Since: January 1, 2008 Posts: 0 Comments: 3370
12z GFS is running
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Goodnight
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Quoting 62. CaribBoy:


Maybe my 10+ inches of rainfall will come.... finally.


Please God give Caribboy the rain he desires !( he gets very grumpy otherwize..)
Member Since: March 1, 2012 Posts: 0 Comments: 6927
Quoting 46. GetReal:




It is trying hard.


93L is a scary storm. If it decides to stall out or creep very slowly it could become a strong hurricane.

But the BOC is a small body of water and 93L doesn't have a lot of West longitude to work with.
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Quoting 59. yoboi:


that is alot of moisture.....when do you think you will dry out???


Who knows ... tend to have lots of rain here ....
Member Since: March 1, 2012 Posts: 0 Comments: 6927
Quoting 20. Tazmanian:
I don't get it how can Boulder turn in too a river

Boulder is built right next to the foothills with a major creek flowing out of the hills right in the middle of town. There is a fairly large area to the west that this creek drains and this flooding is a regular happening, perhaps not this extensive though.
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Quoting 33. CybrTeddy:


ECMWF is showing a very active pattern setting up, unlike what it showed for September.


Maybe my 10+ inches of rainfall will come.... finally.
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Quoting 46. GetReal:




It is trying hard.


ULL could rip it apart too, it certainly isn't helping it at the moment.
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Quoting 52. SouthernIllinois:

UGH!! Back to that old spring pattern huh? lol


Spring ,Most of summer ,autumn and winter pattern..

Are ya still thinking of getting rid of Puff?
Member Since: March 1, 2012 Posts: 0 Comments: 6927
Looks like before all said and done in the GOM, gonna be a full blown hurricane coming
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Quoting 1766. dabirds:
I was in C-U yesterday for some testing, knew you'd been very dry, Monticello looked very dry. They're about as far S as you, right? Got back from Lake Mon., had .25" in guage from Sun., but sure couldn't tell it. Doubt we got that today, but at least had some puddles. StL long range has rain chances all next week, so maybe some relief?


Hey dabirds,

I'm southeast of Monticello, in Tuscola, about 20 miles southeast of there, 25 miles south of Champaign. Long Range from 7-14 says it is supposed to get more moist throughout Illinois, but most of it stays west of the Mississippi. We shall see, this pattern has been one tough one to break.

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56. wpb
The ER-2 has been an invaluable tool for studying tropical cyclone (hurricane) development, tracking, intensification and landfall impacts. During the July 2005 Tropical Cloud Systems and Processes mission based in Costa Rica, the ER-2 carried instruments that measured the buildup and behavior of tropical storm systems over Mexico and Central America and in the eastern Pacific, Caribbean and Gulf of Mexico. The aircraft flew over several hurricanes, including Emily and Dennis that were both violent Category 4-5 storms, and collected information on their entire vertical structure. Data were collected about the temperature, humidity, precipitation and wind related to tropical cyclones and other related phenomena that often lead to development of more powerful storms at sea.
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Quoting 44. FOREX:


If there is no question it is not going to make landfall in the CONUS, save the money. Let the Mexican government invest it.


Rand Paul, is dat yous ?

; )

Member Since: July 3, 2005 Posts: 426 Comments: 128630
Quoting 14. moonlightcowboy:


Wow, yup! Our "bust" folks may be in for a big surprise.


That remains to be seen... but those SSTs are encouraging XD
Member Since: October 6, 2007 Posts: 0 Comments: 6228
From the previous blog
Landfall for 12z NAM (very strong T.S.) in 72 hours
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Quoting 15. SouthernIllinois:

Wazzup Girlfriend? How things over in Ireland Liz??


Hiya Nat .... The usual... Rain :p

Member Since: March 1, 2012 Posts: 0 Comments: 6927
Quoting 31. SouthernIllinois:

Used to put all my eggs in one basket so to speak because I used to think precipitable water was ALONE enough of a presence to pummel someone with heavy rain. But the more I am learning from you and other hard-cores on this blog, it is really more lifting than anything...


You got a lot of rain heading your way as well it appears.
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Quoting 42. VirginIslandsVisitor:


Oh, great... *puts away the pile of paper airplanes*

Morning Joe.

By the way, the word I was looking for earlier was "potable" rather than "city water"...

Lindy



I got ya...GM Lindy!
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.