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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Quoting 1344. KoritheMan:


That's the nature of this blog, lol.

I'm contributing to that until I get my hurricane, so I apologize in advance for that. Maybe. :P


Well yeah it's standard to see but I feel like it's been more vehement than usual, quite a flair for the dramatic.
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Once more we have a ULL interacting (S tip of Tx) that is shearing the NW quadrant of TD10.... thats what is affecting it.... looks like this is the year of ULLs... (another one W Georgia)



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Quoting 1343. KoritheMan:
Remember cat6, you don't want to follow the convection, even with shortwave imagery; those are the upper tropospheric cloud tops. Follow the low cloud lines.


Thanks....
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1346. MrMixon
The list of closed roads in Boulder County is kind of hilariously long...

Boulder Office of Emergency Management

I've spared you all the full list, but here's the beginning. Check the link above or my blog for the full list.

• Boulder Canyon Drive between Boulder and Nederland
• US 36 from McCaslin Boulevard to Flatiron Crossing
• CO 93 (South Foothills Highway) from Greenbriar Boulevard to Eldorado Springs Drive
• Sunset Street from Boston Avenue to Donovan Drive
• Hover Street from Rogers Road to 3rd Avenue
• Ute Highway from 75th Street to McCall Drive
• Hygiene Road from North 75th Street to Crane Hollow Road
• North 75th Street from St. Vrain to Hygiene
• Airport Road from St. Vrain to 9th Avenue
• US 287 from Ken Pratt to Boston Avenue
• 39th Street from Ogallala to Plateau Road
• CO Road 7 from Middle Fork to Plateau Road
• North 95th Street from Valmont Road to Lookout Road
• South 120th Street from Commerce Street to South Boulder Road
• Horizon Avenue from Majestic Drive to Panorama Point
• South 120th Street at Dillon Road
• Spring Valley Road
• Westbound US 36 at McCaslin Boulevard
• Eastbound US 36 at Table Mesa Drive
• SH 157 from US 36 to Pearl Parkway
• US 36 North 95th from Lookout Road to Valmont
• SH 93 from 64th Parkway to SH 128
• Lee Hill Road at Olde Stage Road
• Four Mile Canyon from Boulder Canyon to Poorman
• Bow Mtn Rd from Wagon Wheel Gap to Pine Brook Rd
• 95th from Lookout Road to Valmont Road
• 75th from Jay Road to Valmont Road
• Broadway from Quince to Lee Hill Road
Member Since: March 26, 2006 Posts: 44 Comments: 1520
1345. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #18
Gale Warning
TROPICAL STORM MAN-YI (T1318)
12:00 PM JST September 13 2013
======================================

Ogasawara Waters

At 3:00 AM UTC, Tropical Storm Man-yi (998 hPa) located at 21.5N 142.8E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west at 12 knots.

Gale Force Winds
================
180 NM from the center

Dvorak intensity: T2.5

Forecast and Intensity
=======================
24 HRS: 24.6N 138.9E - 45 knots (CAT 1/Tropical Storm) Sea South Of Japan
45 HRS: 28.6N 137.1E - 55 knots (CAT 2/Severe Tropical Storm) Sea South Of Japan
69 HRS: 34.4N 140.4E - 55 knots (CAT 2/Severe Tropical Storm) Izu Islands Waters
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Quoting 1341. wxgeek723:


Lol slight exaggeration. Ya know, the angst, the arguing.


That's the nature of this blog, lol.

I'm contributing to that until I get my hurricane, so I apologize in advance for that. Maybe. :P
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Remember cat6, you don't want to follow the convection, even with shortwave imagery; those are the upper tropospheric cloud tops. Follow the low cloud lines.
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Quoting 1338. wxgeek723:
So all season we thought a ramp up of activity in the Atlantic would quell the animosity on here...and now that it's finally here the problem is getting worse?


????
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Quoting 1340. KoritheMan:


What animosity?


Lol slight exaggeration. Ya know, the angst, the arguing.
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Quoting 1338. wxgeek723:
So all season we thought a ramp up of activity in the Atlantic would quell the animosity on here...and now that it's finally here the problem is getting worse?


What animosity?
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Quoting 1270. Chicklit:

...not exactly...that guy made inappropriate offers.
I know because I received one.
Strange and sad that was.
Grothar was (and still is) always a gentleman and upright blog citizen.


About a good as a guy gets! +1000
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So all season we thought a ramp up of activity in the Atlantic would quell the animosity on here...and now that it's finally here the problem is getting worse?
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1337. GetReal
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Quoting 1334. cat6band:


You care to elaborate more? I must be missing something if it's that obvious....


Looks to be around 19.7N 94.2W if you follow the shortwave infrared.
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Quoting 1332. GetReal:


Coc almost Stationary but convection seems to move NE.... the slower the stronger it could get...

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Quoting 1330. KoritheMan:


Not really.


You care to elaborate more? I must be missing something if it's that obvious....
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1332. GetReal
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Quoting 1325. TropicalAnalystwx13:

They've been covering it literally all day.


I wouldn't know I'm busy during the day. Gotta take this stuff into consideration. Not to mention the unfolding situation is being exacerbated right now...
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Quoting 1322. cat6band:
It's so hard to see where the LLC is?


Not really.
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1329. GetReal
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Quoting 1261. GatorWX:


It's the widespread totals that worry me. It's a very mountainous region and a very large storm regarding conventive extent.




I know - been in the Texcoco/Puebla area a few times, any significant rain, especially what is being forecast, would be absolutely devastating.
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,
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Notice tha big barrier front that will keep TD10 S of Tx.... Looks like its going to deep in into Fl..

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Quoting 1317. wxgeek723:
Lol you'd think the floods in Colorado would be enough for TWC to break programming but alas, no.

They've been covering it literally all day.
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Quoting 1306. TWTracker99:
Tropical Update!


Is that the sound of a vacuum cleaner for the first 20 seconds? >_>
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1323. GetReal
Quoting 1318. moonlightcowboy:


Is this a northeasterly motion?


I do not believe; that is SW shear giving the illusion of a NE move. However, IMO, the LLC has re-located north of 20N near that new curved blow up of convection.
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It's so hard to see where the LLC is?
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10 looks to be developing a very nice circulation at the surface.

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1320. FWBRuss
DJ, Can you post the moving map for steering currents again. I seem to have lost it. I believe it was a 5 day loop.
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Quoting 1318. moonlightcowboy:


Is this a northeasterly motion?


It sure looks like it...
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Quoting 1313. GetReal:


Is this a northeasterly motion?
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Lol you'd think the floods in Colorado would be enough for TWC to break programming but alas, no.
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1316. GetReal


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Quoting 1313. GetReal:


We have lift-off.
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Quoting 1258. MrMixon:


Thanks for the concern - things are fine here. Since I went to all the trouble to suit up and get water resistant I stayed out until I ran out of light. Things are OK in our immediate vicinity. I mean, they are wetter than I've ever seen them, yes, but the house is high and dry and our driveway is passable. We have mushrooms growing out of our mushrooms and the little wash behind our house, which was bone dry this time last year, is flowing at bank-full. Rain has picked up since the sun went down.



I'm just now getting back online (my wife stole my laptop while I was out walking). Will post updates while I can, but I'm seeing email reports of landlines (telephone) going down in our area and some folks have lost power. Frankly, I'm amazed I've had internet and power all day, save for a few brownouts this morning.

We do have a generator and plenty of propane for boiling water and heating the house (the furnace kicked on a few times last night).


Thanks - but the next time you go out somewhere, and don't let us know your safe. You're grounded! ;)

(Just practicing for when my little one gets a bit older).

Thanks for letting us know (and thank you wife, too - for giving you back the laptop).
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1313. GetReal
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1312. MrMixon
Just heard on the scanner a call for an ambulance in Nederland. Response was that dispatch was skeptical that an ambulance could get to Nederland from Boulder. They are looking for other options...

A quote "we can't get there from here. all the roads are washed out."

Listen here
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1311. flsky
Quoting 1239. ndscott50:
I live at 119 and I-25 about five miles east of longmont colorado. The St. Vrain river is about a mile away and normally is 15 feet across and a foot deep. This morning it was just out of its banks and about a foot short of the bridge. By 10:30am they closed 119 due to the threat off the bridge being overtopped. The water was still a mile from the house. I did some work and then went to leave my house at 3pm. As I walked out a state trooper pulled up and said we had to leave. I asked how long we had and he said you need to leave now. His tone indicated he was series.

In 15 minutes we packed up two kids, two dogs and some clothes and headed out. At that point the fire trucks had arrived and they were just starting to go door to door. When I got to the only road out of the neighborhoods it was flooded and impassable. After turning around I found the state PD. They knocked down a fence at the back of the neighborhood so we could drive out. We still went through over a foot of water.

Latest update from the HOA indicated all ways out of the neighborhood were cut off. Those who stayed were instructed to fill their bath tubs, conserve cell power and shelter on the second floor of their homes. I am glad we acted quickly and the family is now safe with my inlaws in Greeley.

No idea on the status of my house. It was not on a federal flood plain and I was told flood insurance was not needed when I purchased it. My house sits on a high lot a good four or five feet above street level. They are calling this a 500 year flood up stream in Longmont. I am certain the area where my house sits has not flooded in recorded history. It is just amazing that that small river is over a mile wide and in my neighborhood. All I can do is wait to see what the morning brings.


Can only wish you the best of luck. I know your Governor has already declared a disaster for the State. The way things are going, FEMA might be visiting you as well. Be aware, that if your county is declared federally, you will be required to buy flood insurance from now on. FEMA offers the cheapest rates. But all that aside, you'll be in my thoughts and I'm wishing you well. Glad you and the family are safe.
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1310. FWBRuss
Quoting 1308. Tazmanian:



nop TD 10 will be a CA event...
I'll go out on a limb here....It's TD 10 will definately be a GOM event ;)
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1309. KEEPEROFTHEGATE (Mod)
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Quoting 1304. RufusBaker:


Nope will be a west coast of FL event...



nop TD 10 will be a CA event...
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Tropical Update!
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1305. MrMixon
Quoting 1267. Bluestorm5:
We lost Boulder.

@lauren_lanier 55m
Was just told by a police officer that there is no way in it or out of Boulder. All roads to get in or out are barricaded. #boulderflood


I'm not surprised. The rain has kicked up yet another notch over the past 30 minutes. Since this rainy period started about 3 days ago most of the gages around me have reported more than 7". Several gages farther to the north have broken the 11" mark.

I'm having trouble keeping up with all the news, but it seems that Lyons, Estes Park, Jamestown, Gold Hill, Boulder, and Nederland are all isolated (or mostly so) and Longmont is bifurcated by the St. Vrain except for a lone crossing which is being monitored by the police.

I certainly don't plan to travel tomorrow. Hopefully my neighbors are all prepared for a couple days of staying put.
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Quoting 1256. scott39:
Definitely at a TX/LA landfall.


Nope will be a west coast of FL event...
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1303. KEEPEROFTHEGATE (Mod)
Quoting 1300. AussieStorm:
Here is the 9news stream
Link



storm totals

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1302. GetReal
Station 42055 (LLNR 1101) - BAY OF CAMPECHE - 214 NM NE OF Veracruz, MX

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Haven't been to CO since I was a kid but I know every town, neighborhood, bridge, pass just from reading The Stand when I was twelve. All the areas Stephen King described are under emergency. Wishing, praying, hoping the best for Boulder.
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Here is the 9news stream
Link
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okay, well goodnight to all wunderbloggers everywhere...need to try to get an extra hour of sleep tonight.

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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.