Graphic for MPD #0149
MESOSCALE PRECIPITATION DISCUSSION 0149
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EDT WED APR 26 2017

AREAS AFFECTED...AR...SOUTHEAST MO...SOUTHERN IL...EXT WESTERN
KY...EXT NORTHWEST TN

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

VALID 261800Z - 262330Z

SUMMARY...SLOW EASTWARD PROGRESSING LINE WILL UPTICK IN
INTENSITY/EFFICIENCY TOWARD LATE AFTERNOON EARLY EVENING
CONTINUING POSSIBLE FLASH FLOODING THREAT.

DISCUSSION...CURRENT GOES-E AND RADAR MOSAIC DENOTE A CLASSIC
LINEAR SQUALL LINE ADVANCING EASTWARD AHEAD OF WEAKLY DIFFLUENT
UPPER LEVEL PATTERN WITH SHORTWAVE TURNING THE CORNER OF THE BASE
OF THE TROF STARTING TO LIFT NORTHEAST ACROSS N AR INTO S CENTRAL
MO.  THIS SETUP HAS LEAD TO A FAIRLY STRONG UNIDIRECTIONAL DEEP
SWLY FLOW THAT IS NEARLY PARALLEL TO THE CONVECTIVE LINE.  THIS
SUPPORTS CELLS TO TRACK NORTHEAST WITHIN THE LINE AS IT SLOWLY
ADVANCES WITH SOME CORES OCCASIONALLY TRACKING OVER THE SAME AREAS
POSING THE GREATEST THREAT FOR ISOLATED HIGHER TOTALS AND LEADING
TO FLASH FLOODING CONCERNS.  500-1000MB THICKNESS ANALYSIS SHOWS
NARROW AMPLIFIED RIDGING SUGGESTING VERY SLOW EASTWARD ADVANCEMENT
OF THE LINE PARTICULARLY FURTHER SOUTH IN S AR/N LA/NE TX ATTM
WHERE ASSOCIATED C-VECTORS ARE AROUND 5 KTS E OR EVEN SE.   STILL
MODEST SOUTHEASTERLY SFC FLOW AND NARROW CHANNEL OF MODEST
INSTABILITY 500-1000 NORTH CENTAL AR TO SE MO AND 1500-2000 J/KG S
AR ALLOWS FOR THE SLOW BUT STEADY EASTWARD MARCH OF THE LINE. 
ADDITIONALLY...THIS CHANNEL IS FAIRLY MOIST THROUGH THE CLOUD
BEARING/RAINFALL GENERATION LAYERS WITH TPWS OF 1.4" NORTH TO
1.75" SOUTH...LEADING TO RAIN RATES OF 1.25-1.5"/HR CURRENTLY WITH
STRONGEST CELLS ALONG THE LINE...PARTICULARLY FURTHER SOUTH TOWARD
MOISTURE/INSTABILITY MAXIMA.

GOES-E VISIBLE SHOWS SOME BREAKS IN THE CLOUDS ALLOWING FOR SOME
PEAK HEATING/SOLAR INSOLATION TO HELP INCREASE INSTABILITY.  STILL
THE MAIN INCREASE WILL BE DRIVEN BY THE MAIN SHORTWAVE PRESSES
EAST TIGHTENING THE FLOW...STRENGTHENING LOW LEVEL SWLY FLOW AHEAD
OF THE LINE FROM 30KTS TO 50KTS AT 850MB AND ADVECTING BETTER
MOISTURE AND LOW LEVEL WAA TO FEED AND ENHANCE THE CONVECTIVE LINE
OVER THE NEXT 2-3 HRS ACROSS CENTRAL AR.  ADDITIONALLY AS THE
WEAKER LEAD SHORTWAVE LIFTS NORTHEAST THROUGH S MO INTO S
IL...THIS SHOULD SUPPORT A WEAK STALLING OF FORWARD PROGRESSION
(ISALLOBARIC BACKING IN RESPONSE TO THE S/W PASSAGE) ALONG THE
LINE ACROSS SE MO/S IL AS WELL AS ALLOWING FOR FURTHER WESTWARD
EXPANSION OF THE POST-CONVECTIVE LINE MCS CLOUD SHIELD PROVIDING
LONGER DURATION MODERATE RAINFALL (.5-.75"/HR) COMPENSATING FOR
THE SLIGHTLY LESS EFFICIENT CONVECTIVE CORES WITH NORTHWARD
LIMITATION OF GREATER INSTABILITY/MOISTURE.  

GIVEN ALL FACTORS...THERE SHOULD BE A FAIRLY LARGE SWATH OF 2-3"
TOTALS ACROSS THE AREA OF CONCERN WITH EMBEDDED HIGHER TOTALS
POSSIBLE PARTICULARLY ACROSS CENTRAL TO NE AR WHERE BEST ALIGNMENT
OF ALL ENVIRONMENTAL PARAMETERS MAY SETUP.  STILL 3HR FFG VALUES
SEEM TO MATCH THE DIFFERENCES IN EXPECTED RAINFALL MAGNITUDES WITH
 2-2.5" FURTHER NORTH IN SE MO/S IL TRENDING TO 2.5-3.5" ACROSS S
AR.

GREATEST UNCERTAINTY OF TOTAL RAINFALL MAGNITUDES ALSO MATCH UP
WITH THE STEADILY INCREASING FFG VALUES ACROSS S AR INTO NE TX/N
LA AND AS SUCH WILL NOT INCLUDE BUT BASED ON SOME POTENTIAL FOR
CONVECTION/CONVECTIVE LINE TO BE ORIENTED MORE PERPENDICULAR TO
THE INFLOW SUPPORTING GREATER FLUX/RATES AND TRAINING.  WILL
CONTINUE TO MONITOR THIS AREA FOR A MPD LATER IF
CONDITIONS/GROWING SIGNAL FOR FF  WARRANT.  

GALLINA

ATTN...WFO...JAN...LSX...LZK...MEG...PAH...SGF...SHV...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   38668897 37178816 34949027 33969106 33249140
            33189259 33459367 33879418 34359416 35719322
            37459174 38499070


Last Updated: 201 PM EDT WED APR 26 2017