October 3-4 2009: Decaying Tropical System brings
 Severe Weather and Heavy Rain

Alex Tardy, NWS Corpus Christi

 Radar Loops

Morning Analysis

 Model Data

 Severe Storms

Morning Upper Air Data

Midday Analysis

Severe Weather Summary

Evening Upper Air Data

Surface Analysis

Mid Afternoon Analysis

Satellite Imagery

Rainfall Table


  

Click on images for larger view.

Introduction and Background

Showers developed early Saturday morning October 3 2009 and increased in coverage during the afternoon
from north of a line from Laredo to Corpus Christi.  A few storms became severe along and just north of a
surface boundary that was stationary from Encinal to Beeville to Victoria.  Persistent thunderstorms brought
several inches of rain to areas east of I-37 which resulted in local flash flooding.  Showers and thunderstorms
continued through Saturday night before tapering off in the Corpus Christi metro during Sunday morning.  

Figure 1 illustrated the storm total precipitation for October 3-4 2009.  Three supercell tracks are evident
in the image and the widespread heavy rain which occurred along and east of I-37 in South Texas.

STP at 05z

The KCRP WSR-88D loop depicted showers between 0900 and 1200 UTC 3 October and this activity continued
through 1600 UTC from San Antonio to Victoria and over portions of the near-shore waters as the first short wave
trough crossed the region (Fig. 2).


Radar loop (click for larger view)

Radar Loop Oct 3

radar loop

 

Figure 2.  KCRP base reflectivity loops starting 0904 UTC 3 October 2009.   

Upper Air Data

Moisture (precipitable water) had increased over the region and the 1200 UTC sounding at KCRP and
the GFS-MET precipitable water plot was over 2 inches (Fig. 3).

PW plot 12z KCRP sounding

Figure 3.  GFS-MET precipitable water plot at CRP and the 1200 UTC 3 October upper air sounding at KCRP.

The latest Storm Prediction Center (SPC) convective forecast was predicting general thunderstorms
and had a "see text" notation.  SPC sent out an update to the outlook at 1049 am CDT with more details.


1049 am CDT 3 October
...TX...
   STALLED SURFACE BOUNDARY OVER THE SRN TIP OF TX SHOULD REMAIN IN
   PLACE FOR MUCH OF THE DAY...WITH SECONDARY FRONT PERSISTING ALONG
   THE RED RIVER.  VERY UNSTABLE CONDITIONS ARE EXPECTED OVER FAR SRN
   TX WITHIN MOIST WARM SECTOR...ALTHOUGH CAPPING MAY PRECLUDE EWD
   MOVING...ELEVATED STORMS OVER SRN/CENTRAL TX FROM TAPPING THIS
   RESERVOIR OF INSTABILITY.  HOWEVER...MODEST WLY FLOW ALOFT COULD
   SUPPORT SOME ORGANIZATION WITH PERSISTENT UPDRAFTS AND WILL OPT TO
   MAINTAIN LOW SEVERE PROBABILITIES ACCORDINGLY.  MORE WIDESPREAD
   DEVELOPMENT WILL OCCUR WITHIN BROAD LOW LEVEL WAA REGIME ACROSS
   CENTRAL TX THROUGH TODAY...WITH INCREASED WAA AND ELEVATED TSTM
   DEVELOPMENT EXPECTED THROUGH TONIGHT INTO N-CENTRAL/NERN TX AND SRN
   OK.  SOME HAIL COULD ACCOMPANY THIS LATE NIGHT ACTIVITY INTO THE RED
   RIVER VALLEY...ALTHOUGH ACTIVITY SHOULD MAINLY EVOLVE AS MODERATE TO
   HEAVY RAIN GIVEN FAIRLY WARM MID LEVEL TEMPERATURES AND DEEP
   MOISTURE/WEAK LAPSE RATES.
  
   . 10/03/2009

Surface Mesoanalysis 

Since SPC had a boxed mesoanalysis over our CWA there are detailed analyses available.  The data depicts
a boundary (warm front) had lifted into South Texas, located from Encinal (between Laredo and
Cotulla) to just north of Highway 44 (north of Alice but south of George West) eastward to just south of Beeville
and then northeastward to around Victoria (Fig. 4).

 

Surface Winds

Figure 4.  Surface wind and MSL pressure at 1800 UTC.


Considerable surface-based instability existed south of the warm front over deep South Texas
and the northwest Gulf of Mexico as early as 1500 UTC.  Along and north of the boundary there
was considerable Convective Inhibition (CIN).  A high precipitable water plume (theta E ridge)
extended into the Coastal Bend of South Texas (Corpus Christi).  High instability during the warm 
season is common across South Texas but a stronger mid-level CAP is often present
(climatological mean 700 mb temperatures is 10 C during the warm season).  In this case,
considerable wind shear was present over South Central Texas and this resulted in elevated
Energy Helicity and Supercell Composite values (Fig. 5).  The surface plot and moisture
convergence in Figure 6 clearly depicted the boundary in place across the Coastal Bend of
South Texas.

MesoAnalyses (limted activity in our South Texas from1800 to 2000 UTC, but atmosphere
was increasingly unstable with SHEAR south of the surface boundary)


                                                                             

1500 UTC 3 October SBCAPE and CIN   1700 UTC 3 October Precipitable Water 1700 UTC BRN based on MLCAPE 1700 UTC 3 October EHI
SBCAPE at 15z PWAT at 17z BRN at 17z EHI at 17z

Figure 5.  Mesoanalysis for Texas from 1500 to 1700 UTC.

           

Surface Map at 1800 UTC 3 October Surface moisture convergence at 1800 UTC
Surface at 18z moisture convergence at 18z

Figure 6.  Surface plot and surface moisture convergence at 1800 UTC.                                   

By 1900 UTC, the GOES visible satellite image depicted clearing across South Texas
(south of the surface boundary) but convective activity was very limited and entirely north
of the boundary in the form of a few shallow elevated showers (Fig. 7).   It is noteworthy,
that forecast maximum temperatures have been exceeded and most areas south of the
surface boundary were in the lower 90s by 2000 UTC (see Fig. 7).
                           

1800-1900 UTC 3 October 2009                                     

Surface temps warmer than expected Note the clearing south of the surface boundary  Moisture  convergence increasing
Surface Temp clearing skies moisture convergence

Figure 7.  Observed surface temperatures, GOES visible image and surface moisture convergence analysis.

2100 UTC 3 October 2009 

At 2100 UTC, the air mass revealed considerable instability and shear in the heart of South Texas
(Fig. 8).  Large scale warm air advection and insolation brought 10 C 700 mb temperatures into
the southern part of the forecast area and the only convection in deep South Texas was located
along the immediate coast associated with the sea breeze.   A fairly well defined 700 mb short wave
trough was approaching South Texas and forecast to reach the coast by 0300 UTC.
                                            

850 mb and 500 mb shear at 2100 UTC 3 October    SBCAPE at 2100 UTC 3 October (note large values into heart of CWA) 2100 UTC surface plot for South Texas
Shear SB cape surface map
850 mb at 21z 700 mb at 21z 500 mb at 21z
850 mb analysis at 2100 UTC                 700 mb analysis at 2100 UTC                                500 mb at 2100 UTC

Figure 8.  SPC mesoanalyses for South Texas (labelled).


Model Data

The NAM data in Figure 9 supported the radar and satellite imagery (little convective activity and very
little QPF through 0600 UTC 4 October).




                       Note there is NO QPF for much of the CWA                    Note the wetter 0000 UTC NAM (Rio Grande)

1200 UTC 3 October NAM 6-h QPF ending at 00z 4 Oct  1200 UTC 3 October NAM 6-h QPF ending 06z 4 Oct 0000 UTC 3 October NAM total through 48 hours
12z nam ending at 00z 12z NAM 6h ending 06z 4 Oct 00z 3 Oct NAM

Figure. 9.  NAM 6-h QPF from the 1200 UTC 3 October run and NAM run total QPF from the 0000 UTC 3 October run.
 

At 2100 UTC (4 pm CDT), a strong storm developed in the western portion of South Texas
and other isolated cells east of I-37. The cell movement of the strong storm was from the
west to east, while other cells (north of the surface boundary) were shallow and driven
by the southerly low level flow.


Recap of Severe Weather

Warning Statistics

7 SVR warnings
2 TOR warnings
7 FFW warnings
FLW's for Mission River at Refugio, Guadalupe River at Victoria, and Aransas River near Skidmore.
Beeville reported wind damage and 7 inches of rain leading to high water rescues and road closures.


At 2200 UTC a mature supercell had developed in the western part of your CWA, while convective activity
was increasing north of the surface boundary (northern part of the CWA).  The supercell prompted severe
and tornado warnings (Fig. 10).

refl at 22zcross section
VelocitySRV at 2209
Figure 10.  2209 UTC KCRP base reflectivity and cross section of the severe thunderstorm (top).  Bottom
image is velocity and storm relative velocity (270 at 20 kts) at 2209 UTC.

Despite the freezing level being 15,000 feet the hail melting tool (click link) would have indicated very large hail.
Max Hail

This prompted a mesoscale discussion at 2255 UTC (SWOMCD below)
.
  

   MESOSCALE DISCUSSION 2063
   NWS STORM PREDICTION CENTER NORMAN OK
   0555 PM CDT SAT OCT 03 2009
  
   AREAS AFFECTED...SOUTH TX
  
   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
  
   VALID 032255Z - 040030Z
  
   AN ISOLATED TORNADO/WIND DAMAGE POTENTIAL WILL CONTINUE ACROSS FAR
   SOUTH TX...ROUGHLY 50-70 MILES EITHER SIDE OF THE I-37
   CORRIDOR...MAINLY OVER THE NEXT HOUR OR TWO. MARGINAL/LIMITED
   TEMPORAL NATURE OF THE RISK IS STILL EXPECTED TO PRECLUDE A WATCH
   ISSUANCE.
  
   SEVERAL SUPERCELLS WILL CONTINUE TO DEVELOP GENERALLY EASTWARD
   ACROSS FAR SOUTH TX OVER THE NEXT HOUR OR SO IN VICINITY OF A
   ROUGHLY WSW-ENE ORIENTED WARM FRONT. A RATHER MOIST/MODERATELY
   UNSTABLE AIRMASS WITH LOWER 70S F DEWPOINTS IS COMBINING WITH AROUND
   100-150 MS/S2 OF 0-1 KM SRH /PER CRP AND EWD WSR-88D DERIVED DATA/
   FOR AN ENVIRONMENT FAVORABLE FOR LOW LEVEL MESOCYCLONES WITH THE
   POSSIBILITY OF A BRIEF TORNADO AND/OR WIND DAMAGE. WHILE SUCH A
   THREAT MAY CONTINUE OVER THE NEXT HOUR OR SO...SEVERAL FACTORS
   SUGGEST A DIMINISHING SEVERE RISK THEREAFTER...INCLUDING CONTINUED
   STORM MERGERS/INTERFERENCE...A STEADILY INLAND MOVING SEA
   BREEZE...AND LOSS OF DAYTIME HEATING. (storms maintained intensity near I-37
   and eastern part of CWA through the evening).
  
   . 10/03/2009


Another severe thunderstorm developed near Beeville and took on similar characteristics (70 to 75 dBZ
and west to east movement).


Satellite Imagery

water vapor at 00zIR image large view
GOES water vapor imagery depicting the coldest cloud tops over your CWA and a decaying
tropical cyclone in Mexico.

Water Vapor Loop
GOES water vapor loop (click to enlarge) from
2315 UTC 3 October to 1415 UTC 4 October.

Severe Storms and Heavy Rain


cell at 22z

KCRP Composite reflectivity at 2152 UTC 3 October (activity increasing rapidly).

radar at 00z
KCRP base reflectivity at 0010 UTC 4 October.  Note the persistent cells
just east of I-37 where the flash flooding occurred.

Upper Air Sounding

00z 4 October
KCRP upper air sounding at 0000 UTC 4 October 2009.


Local Storm Report/Public Information


PRECIPITATION TOTALS SATURDAY AND SUNDAY (INCHES).

6 miles nw Beeville 7.25
Aransas RAWS 5.12
Seadrift 4.80
Austwell 4.68
Austwell 3.88
Mathis 3.80
Guadalupe Victoria 3.23
Goliad 3.18
Seadrift 2.92
Bloomington 2.77
Beeville 2.67
Port Lavaca 2.49
Goliad 2.42
Goliad 2.16
Victoria 2.10
Victoiria RAWS 2.07
Beeville 2.05
Victoria ASOS 1.74
McMullen site 1.73
Schroeder 1.24
Nueces River Cotulla 1.07
Cotulla 1.04
Tilden 1.00
Orange Grove 0.90
Corpus Christi Naval Station 0.87
Port O'Connor 0.57
Corpus Christi 0.48



WFO Corpus Christi - Alex Tardy

 

...S TX... OUTLOOK for SATURDAY

ONE OR TWO CLUSTERS OF STG...PERHAPS MRGL SVR TSTMS ARE POSSIBLE
ACROSS PORTIONS CENTRAL/S TX EARLY IN PERIOD. THIS ACTIVITY IS
EXPECTED AS ISENTROPIC ASCENT TO LFC OCCURS N OF SFC FRONT...IN
REGIME OF INCREASING LOW LEVEL MOISTURE AND FAVORABLE EFFECTIVE
 SHEAR ALOFT.
PRIMARY FACTOR PRECLUDING CATEGORICAL OUTLOOK ATTM
INCLUDE PRESENCE OF RELATIVELY WEAK MIDLEVEL LAPSE RATES THAT WILL
LIMIT BUOYANCY AND POTENTIAL FOR LARGER HAIL.

MID-UPPER LEVEL CLOUDS AND MOISTURE STREAMING OFF PACIFIC TS OLAF
MAY SOMEWHAT RESTRAIN DIABATIC HEATING WITHIN AND ALONG WARM SIDE OF
FRONTAL ZONE DURING AFTERNOON...AND MOST LIKELY WILL YIELD WEAK
UPPER LEVEL LAPSE RATES. HOWEVER...MODEST DIFFERENTIAL HEATING
ACROSS BOUNDARY MAY CONTRIBUTE TO ADDITIONAL/SFC-BASED/DIURNAL
DEVELOPMENT INVOF FRONTAL ZONE. ANY STG-SVR GUSTS SHOULD OCCUR IN
AND S OF FRONTAL ZONE...WHILE HAIL SIZE SHOULD BE MRGL SVR...AT
BEST...ANYWHERE OVER REGION.


. 10/03/2009

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