MESOSCALE PRECIPITATION DISCUSSION 0082
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 AM EDT THU MAR 29 2018

AREAS AFFECTED...SERN TEXAS...LOUISIANA...SW MISSISSIPPI

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 290714Z - 291300Z

SUMMARY...FLASH FLOODING WILL CONTINUE EARLY THIS MORNING FROM
SOUTHEAST TEXAS INTO PORTIONS OF LOUISIANA AS A LARGE LINE OF
THUNDERSTORMS BEGINS TO PUSH EAST. HOURLY RAIN RATES UP TO 2.0 TO
2.5 IN/HR WILL BE POSSIBLE. FLASH FLOODING MAY DEVELOP INTO
PORTIONS OF MISSISSIPPI AS WELL.

DISCUSSION...AN EXTENSIVE QLCS EXTENDED (AT 07Z) FROM NEAR
VICKSBURG MS...TO ALEXANDRIA LA...TO JASPER TX...TO HOUSTON
TX...TO CORPUS CHRISTI TX. THE SOUTHERN EXTENT OF THE LINE WAS
DEVELOPING INTO A CONTINUOUS LINE SEGMENT AND WAS BEGINNING TO
SHOW STEADIER EASTWARD PROGRESSION. THIS HAS BEEN INDICATED ON A
VARIETY OF CONVECTION ALLOWING MODELS...AND IT MAY PUSH EAST OF
THE SABINE RIVER BY 11-12Z BASED ON RECENT TRENDS. FURTHER
NORTHEAST...INDIVIDUAL CELL MOTION WAS TO THE NE IN PORTIONS OF
LOUISIANA...BUT THE MEAN POSITION OF THE LINE WAS RELATIVELY
STATIONARY AS NEW UPDRAFTS WERE TENDING TO FORM NEAR THE
INTERSECTION OF SOUTHERLY INFLOW FROM THE GULF AND THE EXISTING
COLD POOL AND OUTFLOW BOUNDARY. THIS PORTION OF THE LINE WAS LESS
PROGRESSIVE AND MAY BE MORE FAVORED FOR CONTINUED TRAINING OVER
THE NEXT SEVERAL HOURS. HOWEVER...THE LINE OF STORMS WAS LESS
CONTINUOUS IN THIS AREA LEADING TO SHORTER BURSTS OF HEAVY RAIN.
TO THE REAR OF THE LINE...NUMEROUS FLASH FLOOD WARNINGS WERE IN
EFFECT AS OF 07Z...AND FLASH FLOODING WAS LIKELY ONGOING DUE TO
PERSISTENT HEAVY RAINFALL OVER THE PAST SEVERAL HOURS.

THE LARGE SCALE ENVIRONMENT WILL CONTINUE TO BE SUPPORTIVE OF
HEAVY RAIN RATES. GPS-PW OBSERVATIONS WERE AROUND 1.9 INCHES ALONG
THE TEXAS COAST AND THIS CLOSELY MATCHED CIRA BLENDED TPW PRODUCT.
VALUES EVEN REACHED AROUND 1.6 INCHES INTO NORTHEAST LOUISIANA.
THESE WERE IN THE UPPER ECHELON OF MARCH MONTHLY UPPER AIR
OBSERVATIONAL HISTORY IN THE REGION. ADDITIONALLY...OBJECTIVE RAP
ANALYSIS SHOWED MUCAPE AROUND 1000 J/KG WHICH WILL BE SUPPORTIVE
OF ORGANIZED THUNDERSTORMS.

OBSERVED RAIN RATES HAVE BEEN AS HIGH AS 2 IN/HR ACROSS PORTIONS
OF THE REGION AND THIS WILL CONTINUE TO BE POSSIBLE EARLY THIS
MORNING. A HARRIS COUNTY FLOOD CONTROL DISTRICT RAIN GAGE NEAR
CYPRESS MEASURED 0.48 INCHES OF RAIN IN 5 MINUTES. ALTHOUGH THIS
WAS A SHORT PEAK...IT IS INDICATIVE OF THE UPPER END OF WHAT THE
ENVIRONMENT CAN SUPPORT IN THE HEAVIEST RAIN BANDS. THOSE RATES
CORRESPONDED WITH KDP VALUES ON KHGX OF AROUND 3 DEG/KM...WHICH
MAY BE A REASONABLE PROXY ON RADARS FOR THESE SORT OF EXTREMELY
HIGH INSTANTANEOUS RAIN RATES THIS MORNING.

ONE AREA THAT MAY HAVE A PARTICULARLY ELEVATED RISK OF FLASH
FLOODING WOULD BE FROM JEFFERSON AND ORANGE COUNTIES IN TEXAS
(NEAR BEAUMONT) NORTHEAST TO BEAUREGARD...VERNON AND RAPIDES
PARISHES IN LOUISIANA (NEAR ALEXANDRIA). MRMS AND KLCH DUAL POL
ESTIMATES SHOW AROUND 3-6 INCHES OF RAIN HAS FALLEN IN THIS SWATH
ALREADY TONIGHT...AND THE CREST HYDROLOGIC MODEL CONTINUES TO SHOW
ELEVATED MAX UNIT STREAMFLOW VALUES SUGGESTIVE OF ONGOING
FLOODING. AS ADDITIONAL HEAVY RAIN MOVES INTO THAT AREA...ANY
EXISTING FLOODING COULD BE EXACERBATED AS WE APPROACH SUNRISE.

LAMERS

ATTN...WFO...EWX...FWD...HGX...JAN...LCH...LIX...SHV...

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

LAT...LON   33189034 33188947 32508950 31869005 31099079
            30069154 29579195 29409278 29289385 28639524
            28509616 29199681 30319667 31129575 31759485
            32419370 32789265 32979135