MESOSCALE PRECIPITATION DISCUSSION 0027
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 AM EST THU FEB 22 2018

AREAS AFFECTED...EAST TX...NRN/CTRL LA...SERN AR...NWRN MS

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

VALID 220736Z - 221300Z

SUMMARY...CONTINUED HEAVY RAIN BANDS AND CONVECTIVE CELLS SHOULD
CONTINUE TO MOVE OVER ALREADY SATURATED GROUND INTO THE DAYBREAK
HOURS. THIS MAY ALLOW FOR ONGOING FLASH FLOODING TO PERSIST...OR
FOR LOCALIZED AREAS OF NEW FLASH FLOODING TO DEVELOP.

DISCUSSION...A VARIETY OF RAINFALL ESTIMATES (NSSL QPE, MRMS) AT
06Z INDICATED A BROAD SWATH FROM FAR EASTERN TEXAS INTO SOUTHEAST
AND SOUTH-CENTRAL ARKANSAS HAS RECEIVED AT LEAST 2 INCHES OF RAIN
IN THE PAST 24 HOURS. THE GROUND IN THIS AREA IS VERY LIKELY TO BE
SATURATED...AND ONGOING FLASH FLOOD WARNINGS AND RECENT FLASH
FLOOD REPORTS SUGGEST THAT AREAS OF FLASH FLOODING PERSIST AS OF
0730Z ACROSS PARTS OF THE REGION. GIVEN THE GROUND CONDITIONS AT
THE PRESENT TIME...ANY ADDITIONAL RAINFALL COULD AGGRAVATE
EXISTING FLOODING...OR CAUSE LOCALIZED AREAS OF NEW FLOODING TO
DEVELOP.

SOME FACTORS MAY COMBINE TO REDUCE THE OVERALL SCALE OF THE
HEAVIER (1 IN/HR OR MORE) RAIN RATES OVER THE NEXT FEW HOURS...AND
MAKE THE CONVECTIVE RAIN BANDS MORE SCATTERED IN GENERAL. A
PROMINENT MID-UPPER LEVEL PV ANOMALY CENTERED OVER OKLAHOMA IS
QUICKLY EJECTING NORTHEAST. THE ASSOCIATED NVA BEHIND THAT WOULD
TYPICALLY FAVOR SOME LARGE-SCALE SUBSIDENCE...AND THE AREA WILL
ALSO GET INTO THE RIGHT EXIT REGION OF AN UPPER LEVEL JET STREAK
AROUND 09-12Z...SOMETHING ELSE THAT WOULD FAVOR SUBSIDENCE.
FURTHERMORE...LOW-LEVEL FLOW IS PROJECTED TO BACK SLIGHTLY INTO
THE MORNING HOURS WITH 850MB WINDS BECOMING SOUTHERLY AS OPPOSED
TO SOUTHWESTERLY. THIS MAY INTRODUCE MORE DIRECTIONAL SHEAR
THROUGH THE TROPOSPHERE AND INTERRUPT THE UNIFORM FLOW THAT HAS
FAVORED TRAINING RAIN BANDS THROUGH MUCH OF THE NIGHT THUS FAR.

THAT BEING SAID...BROADLY CONFLUENT...MOIST...AND UNSTABLE
LOW-LEVEL INFLOW CONTINUES ACROSS THE OUTLINED DISCUSSION AREA.
AND REGIONAL RADARS CONTINUE TO SHOW CONVECTIVE CELLS AND SMALL
RAIN BANDS PUSHING NORTHEAST INTO THE SAME AREA. THE OVERALL
THERMODYNAMIC ENVIRONMENT IS NOT EXPECTED TO CHANGE APPRECIABLY IN
THE NEXT SIX HOURS...WITH MARGINAL INSTABILITY AND ABUNDANT DEEP
MOISTURE. GIVEN THE PRESENCE OF HEAVY RAIN BANDS AT THIS
TIME...THE OVERALL MESOSCALE ENVIRONMENT...AND THE CURRENT GROUND
CONDITIONS...FLASH FLOODING SHOULD REMAIN POSSIBLE THROUGH THE
EARLY MORNING HOURS. RAIN RATES OF UP TO 1.5 IN/HR COULD OCCUR
WITH SUFFICIENT TRAINING OF CONVECTIVE CELLS.

LAMERS

ATTN...WFO...HGX...JAN...LCH...LZK...MEG...SHV...

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

LAT...LON   34588914 34148890 33208981 32049134 31259226
            30639314 30329389 30199467 30329522 31149504
            32329396 33429268 34109119 34499016