Flash Flood Guidance
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000
AWUS01 KWNH 210746
FFGMPD
LAZ000-ARZ000-TXZ000-211345-

MESOSCALE PRECIPITATION DISCUSSION 0022
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 AM EST WED FEB 21 2018

AREAS AFFECTED...SOUTHEAST AND EAST TEXAS...FAR WRN LOUISIANA

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

VALID 210745Z - 211345Z

SUMMARY...SHOWERS AND THUNDERSTORMS SHOULD CONTINUE TO DEVELOP AND
ORGANIZE INTO SMALL LINES OR BANDS IN AN UNSTABLE ENVIRONMENT
AHEAD OF A COLD FRONT IN SOUTHEAST TEXAS. HOURLY RAIN RATES OF 1-2
IN/HR ARE EXPECTED WHERE THUNDERSTORMS CAN FAVORABLY TRAIN.

DISCUSSION...A BAND OF THUNDERSTORMS THAT DEVELOPED ALONG THE
MIDDLE TEXAS COAST HAS BECOME A LITTLE MORE EXPANSIVE AS OF 0730Z
AND STRETCHED FROM NEAR BRENHAM TX TO NEAR PORT LAVACA TX. KEWX
AND KCRP DUAL POL ESTIMATES HAVE RAIN RATES APPROACHING 2
IN/HR...AS DOES MRMS. THIS LARGER BURST OF CONVECTION MAY HAVE
BEEN SUFFICIENT TO GENERATE A WEAK MCV PER LONGER RADAR LOOPS
WHICH IMPLY A DEEPER FOCUS FOR CONVECTION AND SHOW AN EROSION OF
RAIN IMMEDIATELY TO THE NORTHWEST AND WEST. THIS MCV WOULD LIKELY
BE EMBEDDED ON THE NORTHERN END OF THE TRAILING STRATIFORM RAIN
NEAR BASTROP TX. THE ASSOCIATED BAND OF THUNDERSTORMS WAS SITUATED
ON THE WESTERN EXTENT OF A REGION OF SCATTERED SHOWER AND
THUNDERSTORM DEVELOPMENT IN SOUTHEAST TEXAS IN AN UNSTABLE
ENVIRONMENT (MLCAPE AROUND 1000 J/KG) ON THE NOSE OF A LOW-LEVEL
MOISTURE TRANSPORT MAXIMUM.

AS THE MCV SLOWLY LIFTS NORTHEAST AND INTERACTS WITH THE EXTENSIVE
SURFACE FRONT...IT MAY CONTINUE TO FOCUS A TRAINING BAND OF HEAVY
RAIN AND THUNDERSTORMS THAT WOULD SHIFT NORTHEAST JUST AHEAD OF
THE COLD FRONT ALONG THE THETAE GRADIENT...AND ON THE NOSE OF THE
STRONGER LOW-LEVEL INFLOW. ADDITIONAL TRAINING OF CONVECTION COULD
ALSO OCCUR FURTHER TO THE EAST IF CONVECTIVE ELEMENTS WERE TO
BECOME DEEPER AND TAP INTO THE MORE SUBSTANTIAL BOUNDARY LAYER
INSTABILITY ACROSS THE REGION. HI-RES MODELS OFFER A VARIETY OF
SCENARIOS AS TO HOW CONVECTION WILL EVOLVE ACROSS EAST TEXAS THIS
MORNING...BUT FROM A PATTERN RECOGNITION STANDPOINT...WOULD EXPECT
THE BEST CHANCE OF HEAVY RAIN TO BE FOCUSED WITHIN THE CHANNEL OF
DEEP MOISTURE WHERE IT OVERLAPS WITH GREATEST BOUNDARY LAYER
INSTABILITY JUST AHEAD OF THE COLD FRONT. OVER THE NEXT SEVERAL
HOURS THIS WOULD BE ROUGHLY FROM NEAR COLLEGE STATION NORTHEAST TO
NEAR SHREVEPORT.

AS HAS ALREADY BEEN ESTIMATED BY RADAR...AND OBSERVED BY SOME
MESONET SITES...RAIN RATES UP TO AROUND 2 IN/HR WILL BE POSSIBLE
GIVEN THE DEEP MOISTURE AVAILABLE. THESE WOULD BE MOST LIKELY
WHERE FOCUSING MECHANISMS ARE READILY AVAILABLE TO FUNNEL
CONVECTIVE ELEMENTS OVER THE SAME AREAS...SUCH AS ON THE DOWNSHEAR
AND SRN FLANK OF THE MCV AS IT APPROACHES THE SYNOPTIC COLD FRONT.

LAMERS

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

ATTN...WFO...CRP...EWX...FWD...HGX...LCH...SHV...

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

LAT...LON   33489414 33259316 32139319 30679346 29809385
            29089482 28169628 27669695 27959731 28719741
            29549715 30819660 31899592


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