MESOSCALE PRECIPITATION DISCUSSION 0270
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
738 PM EDT SAT OCT 05 2013
 
AREAS AFFECTED...EASTERN AR...WESTERN TN...WESTERN KY...SOUTHEAST
IL...SOUTHERN IN...EXTREME NORTHEAST LA...EXTREME SOUTHEAST MO 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 052335Z - 060335Z
 
SUMMARY...MULTIPLE BANDS OF CONVECTION WITH SLOW EASTWARD
PROGRESSION WILL GENERATE 3 HOURLY RAINFALL RATES OF 2-3" WITH
POTENTIALLY HIGHER AMOUNTS ACROSS A PORTION OF THE LOWER
MISSISSIPPI VALLEY NORTHEAST INTO LOWER PORTIONS OF THE OHIO
VALLEY. THESE RAINFALL RATES COULD CAUSE REGIONAL FLASH FLOODING
LATER THIS EVENING. 

DISCUSSION...A DEEP LOW PRESSURE SYSTEM ACROSS THE NORTHERN PLAINS
EARLY THIS EVENING HAS AN OCCLUDED FRONT EXTENDING SOUTHEAST FROM
THE LOW INTO THE UPPER MIDWEST...WHILE FROM THERE A COLD FRONT
EXTENDS SOUTH-SOUTHWEST ACROSS THE MID AND LOWER MISSISSIPPI
VALLEYS. GIVEN THE AMPLITUDE OF THE MID AND UPPER LEVEL
TROUGH...THE SURFACE COLD FRONT IS MORE PERPENDICULAR TO THE
850-300 MB MEAN FLOW THAN OTHERWISE...THEREBY LIMITING THE
EASTWARD PROGRESSION OF THE FRONT.  

TWO MAIN AREAS OF LINEAR CONVECTION WERE NOTED ALONG AND WEST OF
THE OUTLOOK AREA EARLY THIS EVENING. THE FIRST ALONG THE
PRE-FRONTAL TROUGH WHERE THE THERMODYNAMICAL PROFILE IS A BIT MORE
ROBUST (MUCAPES 1000-2000 J/KG)...WHILE THE SECOND
LINE...PREDOMINATELY ALONG THE FRONT... IS BEING SUPPORTED BY MORE
ROBUST UPPER LEVEL DYNAMICS ALONG AN AXIS OF UPPER LEVEL
DIVERGENCE AND LOWER LAYER FRONTOGENESIS. ALONG AND AHEAD OF THE
SURFACE FRONT...STRENGTHENING DEEP-LAYER SOUTH-SOUTH-SOUTHWEST
FLOW AND ATTENDANT MOISTURE FLUX IS POOLING PW VALUES UP TO 1.75
INCHES FROM THE CENTRAL GULF OF MEXICO. 

AS THE LOW LEVEL JET (~850 MB) INCREASES TO 30-40 KTS THIS
EVENING...ALIGNED FAIRLY PARALLEL TO THE 850-300 MB OR APPROXIMATE
CLOUD-BEARING FLOW...ANTICIPATE MORE UPWIND PROPAGATION OF THE
LINEAR CONVECTIVE AND AS A RESULT...SHORTENING CORFIDI VECTORS
OVER THE OUTLOOK AREA. THIS WILL FAVOR BACK BUILDING CELLS WITH AN
OVERALL SLOW EASTWARD PROGRESSION OF BOTH THE FRONTAL AND
PRE-FRONTAL LINES OF CONVECTION. 

IN TERMS OF THE HIGH RESOLUTION NWP GUIDANCE... THE WRF-ARF...NSSL
WRF...AND HRRR ALL SHOW ISOLATED TO SCATTERED POCKETS OF 2-3
INCHES OF GRID SCALE AREAL-AVERAGE RAINFALL ACROSS THE OUTLOOKED
AREA BETWEEN 00-06Z. THESE VALUES ARE AROUND OR IN SOME AREAS
EXCEED THE CURRENT 3 AND 6 HOURLY FLASH FLOOD GUIDANCE ACROSS THE
OUTLOOK AREA. GIVEN THE FAVORABLE COMBINATION OF WARM-SEASON
THERMODYNAMICS (PW'S SOME 2 TO 2.5 STANDARD DEVIATIONS ABOVE
NORMAL) ALONG WITH ROBUST DYNAMICAL FORCING MORE TYPICAL IN EARLY
AUTUMN...BELIEVE REGIONAL FLASH FLOODING WILL BE POSSIBLE.

HURLEY

ATTN...WFO...ILN...LMK...OHX...IND...PAH...ILX...MEG...JAN...
LZK...

ATTN...RFC...LMRFC...NCRFC...OHRFC...

LAT...LON   37048743 35728880 33169083 32719141 32959206 34219146
            36099030 38468833 39318646 39198502 38198578 37048743