OCTOBER: Halloween Storm: Severe Storms/Flash Flood Threat?

[Ptarmigan]

This week could be a wet week. Tropical Storm Octave is likely a factor. Flooding looks likely this week.

[srainhoutx]

Morning update from Jeff:

Wet pattern that began over the weekend will continue through much of this week and possibly through next weekend.

Pair of tropical storms off the Pacific coast of MX (Octave and Priscilla) will continue to send mid and high level tropical moisture ENE to NE across TX as a large scale upper level trough over the western US helps feed to moisture plume in our direction. At the surface another cold front with slightly more push will enter TX on Tuesday and cross off the TX coast on Wednesday. SE winds off the Gulf of Mexico will continue to supply abundant low level moisture and when combined with the tropical connection from the EPAC a saturated air column. PWS continue to come in on soundings in the 2.0-2.3 inch range which supports the heavy rainfall amounts we have seen over the last 24-36 hours.

Deep moisture plume and associated upper air disturbances ejects out of Octave will position across SW into NW TX today with the axis of heavy rainfall from roughly the Big Bend area to Midland to west of Fort Worth. Would not rule out some showers and storms west of I-45 today once temperatures hit 80-85 degrees.  This entire setup begins to shift SE on Tuesday as a cold front progresses across the state. Expect bands of slow moving thunderstorms producing torrential rainfall to develop Tuesday afternoon and evening across central TX into the NW portions of SE TX along and ahead of the frontal boundary. Given the favorable setup into the evening hours of decent Gulf inflow through the night and stream moisture from Octave excessive rainfall will be possible leading to rapid flash flooding especially across central TX and areas that were hard hit this weekend. It is nearly impossible to predict where these isolated “great” rainfall amounts will occur until they are in progress as we saw on Saturday and Sunday. These storms tend to develop and then just sit and rain at 3-4 inches per hour for 3-4 hours resulting in 10+ inches of rainfall.

Cold front should push to the coast by Wednesday with the axis of heavy rainfall shifting offshore. Upper trough remains anchored to our west so both Pacific and Gulf moisture will overrun the frontal slope with light rain continuing into Thursday morning. Temperatures will fall during the day on Wednesday from the 70’s ahead of the front into the 60’s behind the boundary and it will feel cold with north winds, cloudy skies, and rain.

May see a quick break in the light rains on Thursday before another stronger disturbance moves through the trough and increases overrunning Friday into Saturday. Could see widespread light to moderate rainfall Friday-Saturday as warm moist air is lift over the cold air at the surface. Will probably need some higher rain chances in the Friday-Saturday period, but we are still several days out.

Hydro:

Flood Warning for the upper San Bernard River and Colorado River at Bastrop and LaGrange have been cancelled. Flooding is no longer forecast on these river basins.  

Flood Warning is in effect for the Nueces River at Asherton and Cotulla. Moderate to major flooding is forecasted due to rainfall of 8-12 inches over the river basin yesterday.

 

 




 

 

 

[Ptarmigan]

Here is a 8 to 14 day analog forecast.



Some of them raise an eyebrow as heavy rain fell not too long after the dates mentioned.
10/8/1993-Heavy rain on October 20 and freeze on Halloween.
10/12/2006-Heavy rain on October 15 to 18.
10/8/2009-Heavy rain throughout October.

[srainhoutx]

All the ingredients for a classic October Flood event are developing across a large portion of the Lone Star State later today. Rich tropical moisture is streaming inland off the Gulf with PW's near or above 2 inches which is 2 Standard Deviations above normal, mid/high level EPAC tropical moisture from Octave and a slow moving frontal boundary are all combining from the Edwards Plateau, Hill Country and on NE toward the Arklatex that may generate efficient rainfall rates of 1-2 inch per hour with isolated 3-5 inch per hour rates across areas that saw in excess of 12 inches of rainfall last Saturday night/early Sunday near the Austin Area.

[srainhoutx]

Morning update from Jeff:

Factors coming together to produce another heavy to excessive rainfall event from late this afternoon into tonight across central and N TX and possibly into the northern counties of SE TX.

Cold front surging southward this morning extending from near Lubbock to Norman will continue southward today reaching N and C TX this afternoon. TD Octave is making landfall along the Baja of Mexico and spreading mid and upper level moisture NE across TX ahead of the frontal boundary. Upper level ridging is nosing into the coastal areas from the Gulf of Mexico along with a slightly drier air mass.

Expect a significant increase in thunderstorm activity this afternoon along the frontal boundary from SW TX to the Dallas area where slow moving excessive rainfall will be possible. PWS at or above 2.0 inches support an excessive rainfall threat and slow storm motions may result in several inches. Flash Flood watches are in effect for central TX where flooding rainfall occurred on Sunday and river flood waves are still working downstream.

Expect a band of convection with heavy rainfall to move into SE TX overnight and gradually weaken as the best upper level support remains north of I-10 and greatest moisture is found in roughly the same area. Moisture will decrease toward the coast and expect a fairly strong rainfall gradient of 2-3 inches over our northwest counties to possibly less than .25 of an inch along the coast. Soils are fairly wet over the NW counties where heavy rains fell on Saturday and Sunday and additional rainfall will run-off possibly causing some localized flooding concerns. At this time it appears most of the excessive rainfall will remain north and west of the metro areas.

Cold front pushes off the coast on Wednesday with much cooler conditions. Main upper level trough lags well behind the boundary over the SW US keeps a moist Pacific flow in place in the upper levels. Expect only a gradual tapering of light rain on Wednesday into early Thursday. It will be much cooler with cloudy skies and north winds and expect some areas will remain in the 60’s on Wednesday. Dry period Thursday-Friday will be short lived as the main trough over the SW US ejects a strong short wave trough across TX on Friday into Saturday. Coastal trough will be forced off the lower TX coast which will encourage moisture to flow up and over the surface cool dome. Expect showers and thunderstorms to develop from the coastal bend NE into SE TX Friday afternoon into Saturday morning. Could see a few strong storms given some elevated instability.

Still does not look to really clear out even behind this short wave as the main upper trough remains anchored to our west continuing a moist flow over the top of the cool dome at the surface keeping mostly cloudy and cool conditions in place. A much stronger front at some point next week may finally push the clouds and moisture south of the area.    

 

 

 

 

[srainhoutx]

From Nesdis:

SATELLITE PRECIPITATION ESTIMATES..DATE/TIME 10/15/13 1206Z
SATELLITE ANALYSIS BRANCH/NESDIS---NPPU---TEL.301-683-1404
LATEST DATA USED: GOES-13 1145Z GOES-15 1141Z WARREN
.
LOCATION...ARKANSAS...TEXAS...OKLAHOMA...
.
ATTN WFOS...LZK...SHV...TSA...FWD...OUN...EWX...SJT...LUB...MAF...
ATTN RFCS...LMRFC...ABRFC...WGRFC...
.
EVENT...HEAVY RAINS
.
SATELLITE ANALYSIS AND TRENDS...EARLY STAGES OF ANTICIPATED NEXT ROUND
OF HEAVY RAINS DEVELOPING ACROSS PORTIONS OF SOUTHWEST AND CENTRAL TX
THIS MORNING. LATEST WATER VAPOR LOOP SHOWS TWO SHORTWAVE IMPULSES
RIDING ALONG RATHER MOIST BAROCLINIC ZONE...ONE CROSSING THE SRN TX
PANHANDLE...WHILE THE SECOND...FARTHER S IS JUST EMERGING FROM MEXICO
ACROSS SW TX. SHOWERS AND TSTMS BREAKING OUT ALONG SFC FRONTAL BOUNDARY
ACROSS N-CENTRAL TX HAVE SHOWN LITTLE EWD PROGRESSION OVER THE PAST HR.
SFC MOISTURE CONVERGENCE AHEAD OF FRONT IS RATHER IMPRESSIVE WITH SWRLY
25 KT FLOW AT 85H PER VWPS. BLENDED TPW PRODUCT SUGGESTS MAX VALUES
STRETCHING ACROSS CENTRAL TX AROUND 1.7". HIGH CLOUDS STREAMING ACROSS
NRN TX ARE OBSCURING ANY GOOD CLOUD SIGNATURES IN IR IMAGERY...HOWEVER
FARTHER S AHEAD OF THAT SECOND SHORTWAVE TEXTURED AND COOLING CLOUD
TOPS ARE NOTED OVER TERRELL/CROCKETT/IRION COUNTIES. BOTH AREAS
OF SHOWERS/TSTMS ARE BECOMING MORE ELONGATED WITH TIME FROM SW TO
NE...INCREASING THE THREAT OF TRAINING.
.
AN ANNOTATED SATELLITE GRAPHIC SHOWING THE HEAVY PRECIPITATION
THREAT AREA SHOULD BE AVAILABLE ON THE INTERNET ADDRESS LISTED
BELOW IN APPROXIMATELY 10-15 MINUTES.
.
SHORT TERM OUTLOOK VALID 1200-1800Z...MEDIUM-HIGH CONFIDENCE FACTOR
IN SHORT TERM OUTLOOK...UL DIFFLUENCE AND VERTICAL ASCENT IS EXPECTED TO
STRENGTHEN THROUGHOUT THE MORNING INTO THE AFTERNOON ACROSS CENTRAL TX
AHEAD OF MID TO UL LOW CROSSING NRN MEXICO...OF WHICH ARE THE REMNANTS
OF OCTAVE. MULTIPLE SHORTWAVES OUT AHEAD OF MID TO UL LOW SHOULD CONTINUE
TO PROVIDE SUPPORT TO DEVELOPING AREAS OF SHOWERS/TSTMS ACROSS CENTRAL TX
THIS MORNING. GREATEST CONCERN IS TRAINING OF HEAVY RAINS IN RELATIVELY
UNIFORM SW TO NE FLOW MID TO UL REGIME. THE SRN CLUSTER OF SHOWERS/TSTMS
APPEARS TO BE THE BEST ORGANIZED ATTM AND IS LIKELY PRODUCING RAINFALL
RATES NEARING 1.75-2.0"/HR. LLVL MOISTURE FROM OCTAVE DOES NOT APPEAR TO
HAVE MADE IT ACROSS THE MOUNTAINS OF NRN MEXICO...BUT THIS IS EXPECTED
LATER IN THE DAY...LIKELY COINCIDING WITH MID TO UL LOW RIDING ALONG
FRONTAL BOUNDARY ACROSS CENTRAL TX...LEADING TO POSSIBLE WIDESPREAD
MODERATE TO HEAVY RAINS FROM CENTRAL TX THROUGH SE OK/SW AR.

[srainhoutx]

I wanted to touch briefly on the signals that the longer range guidance are beginning to suggest. As has been mentioned and many folks know, the Western Pacific has been very active with several very strong tropical cyclones and that continues today. Typhoon Wipha, a very large cyclone will turn ENE across the Pacific and transition into a very large extra tropical system and bring about a significant pattern change across North America along and E of the Rockies. A early season cold air mass has been developing across Eurasia and will be dislodge and drop S into our source regions for cold air in Eastern Alaska and Western Canada. A strong Polar front will develop and dive S along and E of the Rockies as a ridge of high pressure build near the West Coast causing a very big buckle in the Polar jet. While we are still about 10 days out and things may well change, the cold weather lovers may well see that first true ‘Blue Norther’ near the Halloween time frame or just before. Tis the season.

[Portastorm]

It won't take much rain in a short period of time in Austin to turn things into a flash flood situation. Portions of south, southwest, and west Austin as well as Pflugerville received anywhere from 8-12 inches of rain over the weekend. Ground is saturated. Right now EWX says 1-2 inches likely with 3-5 possible. Wouldn't surprise me to see more in certain areas as this is a classic Rosa Redux (1998?) situation. Stay tuned every body!

[srainhoutx]

Very cool picture from NWS Midland/Odessa via facebook of the cold front roll cloud approaching that area.

[Ptarmigan]

It won't take much rain in a short period of time in Austin to turn things into a flash flood situation. Portions of south, southwest, and west Austin as well as Pflugerville received anywhere from 8-12 inches of rain over the weekend. Ground is saturated. Right now EWX says 1-2 inches likely with 3-5 possible. Wouldn't surprise me to see more in certain areas as this is a classic Rosa Redux (1998?) situation. Stay tuned every body!

Rosa happened in 1994. That led to the deadly October 1994 Flood in Southeast Texas. 1998 was from Hurricane Madeline. Both had 30 inch rainfall totals.

[ticka1]

http://weather.rap.ucar.edu/surface/dis ... duration=0






For those that want to track the front southward progression.

[srainhoutx]

The latest RUC short range model suggest the frontal boundary is slowing down as it approaches Central Texas. The latest HRRR high resolution rapid refresh guidance is also suggesting increasing storm coverage across the Edwards Plateau/Hill Country with training storms and squalls with very heavy slow moving rainfall rates in excess of 2-3 inches per hour increasing the Flash Flooding threat as a couple of strong short wave disturbances move ENE out of Mexico toward Texas.

[Portastorm]

The latest RUC short range model suggest the frontal boundary is slowing down as it approaches Central Texas. The latest HRRR high resolution rapid refresh guidance is also suggesting increasing storm coverage across the Edwards Plateau/Hill Country with training storms and squalls with very heavy slow moving rainfall rates in excess of 2-3 inches per hour increasing the Flash Flooding threat as a couple of strong short wave disturbances move ENE out of Mexico toward Texas.

Yeah, EWX alludes to this in the lunchtime AFD they released. Unfortunately the concerns for a serious flash flood event appear to be warranted. Wouldn't surprise me if this ends up as one of those "events" where EMS folks are plucking people out of trees and it makes the national news.

[djmike]

Latest QPF has shifted the bulk of moisture eastward towards the coast. Attached is the 7-day showing 2.50" or more for the Houston/Beaumont area. 5-day also shows similar. Hope to see ALL of Texas get some beneficial drought busting rains! Just not all at once to cause problems and flooding.

qpf.PNG (56.2 KiB) Viewed 4315 times

[djmike]

Thoughts? I would have figured a little more precip with tomorrows frontal passage. LCNWS has bumped Beaumonts precip % to 60 for tomorrow.

Courtesy of KFDM 6 in Beaumont:

7day2.PNG (209.74 KiB) Viewed 4286 times

[TexasBreeze]

NWS Houston isn't too enthusiastic with rain chances or amounts for Houston metro with the front.

[srainhoutx]

Rain chances for SE Texas appear to increase behind the front as a Coastal low/trough develops and over running showers/elevated storms increase as embedded upper air disturbance ride the sub tropical jet into the weekend.

[Paul Robison]

Read:

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 150859
SPC AC 150859

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT TUE OCT 15 2013

VALID 181200Z - 231200Z

...DISCUSSION...
...DISCUSSION...

CONSENSUS AMONG LONG RANGE MODELS INCLUDING ENSEMBLE MEMBERS IS THAT
A BROAD POSITIVE TILT UPPER TROUGH WILL CONTINUE TO AMPLIFY ACROSS
THE CNTRL U.S. DAY 4. A MEAN SYNOPTIC TROUGH WILL LIKELY PERSIST IN
SOME FORM OVER THE ERN HALF OF THE U.S. THROUGH MOST OF THE 4-8
PERIOD. INDICATIONS ARE THAT PARTIALLY MODIFIED GULF AIR WILL BEGIN
RETURNING NWD THROUGH S TX AND THE WRN GULF COASTAL REGION LATER DAY
4 /FRIDAY/ AHEAD OF A COLD FRONT IN ASSOCIATION WITH THE AMPLIFYING
TROUGH. HOWEVER...IT APPEARS INSUFFICIENT TIME MAY EXIST FOR A MORE
ROBUST RETURN OF MOISTURE BEFORE THE COLD FRONT REACHES THE COAST.
THEREFORE...ANY SEVERE THREAT APPEARS VERY MARGINAL AT THIS TIME.
OTHERWISE...THIS PATTERN WILL GENERALLY BE CONDUCIVE TO OFFSHORE
FLOW OVER THE GULF AND STABLE CONDITIONS INLAND.

[Ptarmigan]

Heavy rainfall forecasting training manual
http://www.hpc.ncep.noaa.gov/research/m ... t_test.htm

Original Maddox et al. MCS archtypes associated with flash flooding
http://www.hpc.ncep.noaa.gov/research/m ... age907.htm

Features In Flooding Events
1). Most flash floods were associated with convective storms.
2). Storms occurred where surface dew points were high.
3). Relatively high moisture contents were present through a deep tropospheric layer.
4). Weak to moderate vertical wind shear was present through the cloud depth.
5). Convective storms and/or cells repeatedly moved over the same area.
6). A weak, mid-tropospheric, Meso-a scale trough helped to trigger and focus the storms.
7). The storm position was very near the mid-tropospheric, large-scale ridge position.
8). Storms often occurred during the nighttime hours. Remember the bulk of the Maddox MCCs were located in the Plains

[skidog40]

lots of rain maybe training effect, ice age number 5 coming