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Great Southern Plains Flood of 2015


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Probably should have put a size/scope qualifier in there. Allison was incredible, but actually fairly localized. In terms of huge area affected by massive amounts of rainfall, perhaps the most notable tropical cyclone is Hurricane Beulah from 1967. Eastern Pacific tropical cyclones have also contributed to massive floods here, particularly those in October 1994 and October 1998.

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Allison?

tropical storm Allison in June of 2001... Was pretty meh as far as winds and pressure go, but caused significant rainfall over southern/southeastern U.S, and historic rainfall in Texas (especially in Houston).
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Epic, all-time record flooding going on in the San Marcos, Texas area early this morning. Dozens of water rescues, cars washed away, homes flooded, and at least one bridge destroyed on the Blanco River.

 

per NWS San Antonio's Twitter page:

 

It appears that we have lost the Blanco River @ Wimberley, which has not reported since about 1am. At that time, the gauge was at 40.21 ft.

 

Medina Lake has risen 22 feet in just 7 hours!

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Onion Creek and apparently Williamson Creek here in Austin flooded as well, but luckily not like areas just south of here. Camp Mabry hasn't reported since the first round of storms last night, and Austin Bergstrom Airport had a 75 mph gust. Lots of wind damage all over town today.

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well, last night at 1am when i sent out the tweet telling San Marcos to get away from the Blanco RIver, i have to admit, it was one of those times i looked at the streamflow and the rainfall, looked at where that river ran, and just by instinct asked people to get out of the way as that wall of water was about to come down.

 

Hopefully I wasn't out of line in how I did it before NWS-EWX, but it was just one of those things where if I didn't do it, I didn't know who would at that time in the morning. in retrospect, it looked like an excellent call, but I hope my meteorological colleagues down there don't feel I did wrong with my timing.

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Onion Creek and apparently Williamson Creek here in Austin flooded as well, but luckily not like areas just south of here. Camp Mabry hasn't reported since the first round of storms last night, and Austin Bergstrom Airport had a 75 mph gust. Lots of wind damage all over town today.

Buda received 3 inches of rain last night. It was pretty windy around 330am on Sunday. I am not sure how strong the wind gusted, but it blew down a tree on my relatives' property and it blew down the fencing at the local YMCA where they are building new indoor basketball courts.

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Buda received 3 inches of rain last night. It was pretty windy around 330am on Sunday. I am not sure how strong the wind gusted, but it blew down a tree on my relatives' property and it blew down the fencing at the local YMCA where they are building new indoor basketball courts.

I live on the southwest side of Austin, near Barton Creek, and the winds were very intense for a couple of minutes. I'd say it was 60 mph if not more. I went through Irene and Sandy on Long Island, and I'd say the winds were as strong as Irene, which gusted 65-70 mph where I was. Visibility was near zero with the heavy rain. The tornado warning we had made me skip a couple of heartbeats, especially when strong rotation was indicated, albeit briefly, and as the storm was changing direction to more northerly and away from very populated areas. I drove through Zilker Park today and noticed some downed trees, and Barton Creek was a torrent. Part of 360/onto Mopac was closed off from the flooding. The east side of Austin seems to have had the most wind related damage-the airport suffered some bad wind damage and an official 75 mph gust, an apartment building had much of its roof ripped off, and lots of power/tree damage there. 

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Tricky forecast at the southern end today. At this point, I'm expecting convective initiation pretty far into Texas along the southern Balconies. If these storms develop a strong cold pool like what should occur with the main part of the MCS to the north, storms could kick out fairly quickly. However if the cold pool from these storms is not very strong, the southern Hill Country and areas a little east will be in for a world of hurt today with moist and unstable air feeding into a slowly eastward pivoting line. High-Resolution guidance has been waffling back and forth between solutions, so how bad flooding may actually be today will likely be a nowcast.

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WPC discussion mentioned the possibility of extreme rainfall rates in the hard-hit southern Edwards Plateau.

 

mcd0126.gif

 

MESOSCALE PRECIPITATION DISCUSSION 0126
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1004 AM EDT MON MAY 25 2015

AREAS AFFECTED...NORTHERN AND CENTRAL TEXAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 251404Z - 251904Z

SUMMARY...FLASH FLOODING IS POSSIBLE ACROSS PORTIONS OF NORTHERN
AND CENTRAL TEXAS IN ASSOCIATION WITH A FORWARD PROPAGATING MCS.

DISCUSSION...RADAR AND ADDITIONAL ANALYSES SHOW THE EARLY STAGES
OF A FORWARD PROPAGATING MCS FORMING ACROSS WEST CENTRAL TEXAS IN
ASSOCIATION WITH A COMPACT AND VIGOROUS SHORTWAVE TROUGH. WHILE
INTEGRATED MOISTURE VALUES ARE ONLY MODEST...STEEP MID LEVEL LAPSE
RATES AND DEEP/STRONG ASCENT ARE SUPPORTING DEEP CONVECTION WITH
HOURLY RAINFALL RATES NEARING 2 INCHES...WHICH IF SUSTAINED IS
SUFFICIENT TO EXCEED LOCAL FFG VALUES.

THE 00Z GEM REGIONAL AND 00Z NAM CONUS NEST BEST ALIGN WITH THE
OBSERVED RADAR PATTERN AT FORECAST ISSUANCE AND THUS WERE USED TO
EXTRAPOLATE THE MCS AS IT CONTINUES TO GROW INTO THE AFTERNOON.
THE MOST LIKELY AREA FOR RATES TO EXCEED GUIDANCE WILL BE ALONG
THE PATH OF THE MESOLOW THAT IS EXPECTED TO REMAIN ALONG BUT
MAINLY NORTH OF I-20 AND WEST OF I-35 THROUGH 18-19Z. ANOTHER
POSSIBLE AREA WILL BE NORTHWEST OF SAN ANTONIO...WHERE SUPERCELLS
IN A VERY HIGH CAPE ENVIRONMENT MAY PRODUCE SOME EXTREME RAINFALL
RATES.

JAMES

ATTN...WFO...EWX...FWD...LUB...MAF...OUN...SJT...

ATTN...RFC...ABRFC...WGRFC...

LAT...LON 33649958 33619812 32909734 31179727 29899803
29349945 29690058 30540038 31360020 32170053
32510111 33080082 

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Low lying areas near downtown are completely underwater. Streets look like raging rivers on the local news. Austin is crisscrossed by numerous creeks, and they are all rising fast. The rain is finally shifting east, but 5-7" of rain has fallen on the west and north sides of town, where a lot of these streams are fed. 

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I'd say this event can be classified as a Synoptic Maddox flood event. These storms are only very slowly propagating east while being fed by a 40 kt low level jet and with strong forcing for ascent from the right entrance region of an upper level jet streak. Upstream airmass feeding into these storms is characterized by dewpoints 75*F or greater, ML CAPE in excess of 4500 J/kg, and PWs greater than 2.00". As long as the band only slowly pivots east, there will be some insane rainfall totals across south-central Texas.

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A couple of photos from after the deluge today: one is a photo of a drainage basin for Barton Creek which became a torrent after the rain today-I've never seen it more than basically a big puddle before today. Another is a cool shot of the mammatus deck we've been under from my apartment. post-76-0-58332800-1432604804_thumb.jpgpost-76-0-47813100-1432604854_thumb.jpg

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Harris County is in a bad spot. Inflow storms are merging with the main line over the county with storms upstream set to train over the same area. There's probably going to be several reports of over 5" there tonight.

Already 1.97" in an hour

 

KIAH 260253Z 34012G17KT 1SM +TSRA SCT009 BKN017CB OVC028 19/18 A2990 RMK AO2 PK WND 35027/0202 WSHFT 0146 PRESFR SLP123 CONS LTGICCCCG ALQDS TS ALQDS MOV NE P0197 60197 T01890183 50015

 

I wouldn't be shocked if they pick up at least 6" of rain.

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Already 1.97" in an hour

 

KIAH 260253Z 34012G17KT 1SM +TSRA SCT009 BKN017CB OVC028 19/18 A2990 RMK AO2 PK WND 35027/0202 WSHFT 0146 PRESFR SLP123 CONS LTGICCCCG ALQDS TS ALQDS MOV NE P0197 60197 T01890183 50015

 

I wouldn't be shocked if they pick up at least 6" of rain.

 

Headed that way quickly. Harris County Flood Control District gauges have seen over four inches of rain in one hour in some cases. One gauge even saw .88" in just five minutes!

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Already 1.97" in an hour

KIAH 260253Z 34012G17KT 1SM +TSRA SCT009 BKN017CB OVC028 19/18 A2990 RMK AO2 PK WND 35027/0202 WSHFT 0146 PRESFR SLP123 CONS LTGICCCCG ALQDS TS ALQDS MOV NE P0197 60197 T01890183 50015

I wouldn't be shocked if they pick up at least 6" of rain.

Back on the evening of June 29, 2014 parts of Cedar Rapids, Iowa got 6 inches of rain in just 45 minutes. The following afternoon was the derecho that left 45,000 customers without power, the most since July 20, 2003.

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4-7" of rain northwest of Houston, in a short time frame (2+ hours), as per KHGX radar

 

---

 

* FLASH FLOOD WARNING FOR...
  CENTRAL HARRIS COUNTY IN SOUTHEASTERN TEXAS...
  NORTHEASTERN FORT BEND COUNTY IN SOUTHEASTERN TEXAS...

* UNTIL 1245 AM CDT
    
* AT 1047 PM CDT...DOPPLER RADAR INDICATED A THUNDERSTORM PRODUCING
  HEAVY RAIN ACROSS THE WARNED AREA. 5 TO 7 INCHES OF RAIN HAVE
  FALLEN. FLASH FLOODING IS EXPECTED TO BEGIN SHORTLY.

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