Flash Flood Guidance
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000
AWUS01 KWNH 201402
FFGMPD
LAZ000-TXZ000-201800-

MESOSCALE PRECIPITATION DISCUSSION 0894...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1002 AM EDT FRI OCT 20 2017

CORRECTED FOR TYPO IN LAST PARAGRAPH

AREAS AFFECTED...SERN TX

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

VALID 201351Z - 201800Z

SUMMARY...PERIODS OF TRAINING HEAVY RAIN ARE EXPECTED TO CONTINUE
THROUGH THE REMAINDER OF THE MORNING ACROSS PORTIONS OF SERN TX.
SOME EASTWARD MOVEMENT TOWARD SWRN LA IS POSSIBLE BY 18Z WITH
LOCAL 4-6 INCH TOTALS NEAR THE COAST.

DISCUSSION...WATER VAPOR IMAGERY SHOWED A SHORTWAVE TROUGH MOVING
INTO OK AS OF 13Z WITH THE TAIL END OF THE SHORTWAVE EXTENDING
TOWARD THE MIDDLE TX COAST. WINDS ALOFT WERE DIFFLUENT AHEAD OF
THE TROUGH AXIS OVER ERN TX LIKELY ADDING TO VERTICAL LIFT THROUGH
THE COLUMN. LOOPS OF INFRARED IMAGERY SINCE 00Z ALSO HINTED AT
PERHAPS A WEAK VORTICITY MAX THAT TRACKED NORTH FROM THE GULF INTO
SERN TX TIED TO A BURST OF CONVECTION EARLIER THIS MORNING.
OBSERVED RAINFALL RATES TIED TO THAT BURST FROM 10Z IN NRN
GALVESTON COUNTY WERE ABOUT 5 IN/HR COINCIDENT WITH GPS
PRECIPITABLE WATER VALUES OF 1.8 TO 2.0 INCHES. KLCH AND KHGX
RAINFALL ESTIMATES SHOWED 3-4 INCHES HERE AND CONTINUE TO BE
UNDERDONE WITH ONGOING RAINFALL OVER THE REGION.

RAP ANALYSIS WINDS AT 850 MB WERE SIMILAR TO VAD WIND PLOTS FROM
KHGX...TIAH AND KLCH...THOUGH THE RAP WIND SPEEDS WERE A BIT
WEAKER THAN OBSERVATIONS SUGGESTING STRONGER CONVERGENCE THROUGH
13Z. FLOW WAS CONVERGENT IN THE LOW LEVELS HELPING TO FOCUS A
BROKEN LINE OF CONVECTION THAT EXTENDED FROM JUST EAST OF
GALVESTON BAY INTO THE GULF OF MEXICO.

SHORT TERM FORECASTS FROM THE RAP SHOW VERY SLOW MOVEMENT TO THE
TAIL END OF THE SHORTWAVE TROUGH AXIS OVER ERN TX WHICH KEEPS THE
AREA UNDER DIFFLUENT FLOW THROUGH AT LEAST 18Z. THE RAP ALSO SLOWS
A CONTINUATION OF THE LOW LEVEL CONVERGENCE AXIS WHICH IS EXPECTED
TO HELP CONTINUE A FOCUS FOR ADDITIONAL CONVECTION THROUGH THE
MORNING. IT APPEARS THE RAINFALL AXIS WILL NOT DRIFT BACK TO THE
WEST...BUT THE MPD THREAT AREA COVERS THE EASTERN HOUSTON METRO TO
ACCOUNT FOR POSSIBLE WOBBLES IN THE AXIS. THE NORTHWARD EXTENT OF
HEAVY RAINFALL SHOULD BE LIMITED BY REDUCED INSTABILITY TO THE
NORTH...FOCUSING THE GREATEST THREAT FOR AN ADDITIONAL 4-6 INCHES
TO LOCATIONS WITHIN 50-75 MILES OF THE COAST.

OTTO

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...HGX...LCH...

ATTN...RFC...LMRFC...WGRFC...

LAT...LON   30699440 30599399 30479371 30289363 29729351
            28929388 28909496 30119515 30569497


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