MESOSCALE PRECIPITATION DISCUSSION 0775
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
506 PM EDT THU AUG 31 2017

AREAS AFFECTED...CENTRAL TN...NORTHERN AL

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

VALID 312105Z - 010030Z

SUMMARY...EASTWARD EXPANSION OF FLASH FLOODING THREAT ALONG
DEFORMATION ZONE AND POTENTIAL TRAINING CELLS WITHIN WARM SECTOR.

DISCUSSION...CURRENT WSR-88D REFLECTIVITY MOSAIC/RAP ANALYSIS
FIELDS DEPICT AN EXPANDING LINE OF NARROW ELEVATED UPDRAFTS ACROSS
N CENTRAL TN.  THIS APPEARS TO BE THE LINGERING/OLD TROWAL WRAPPED
BACK FROM WARM CONVEYOR BELT FURTHER EAST FROM NC ACROSS E TN. 
VWP NETWORK ALSO SUGGESTS STRENGTHENING 7H SELY FLOW INTERSECTING
WITH THIS BOUNDARY AROUND 7-6H SUPPORTING MID-LEVEL FRONTOGENETIC
FORCING FOR THIS CONVECTIVE DEVELOPMENT PRECURSORY TO BETTER AND
LOWER LEVEL ASCENT APPROACHING FROM THE SOUTH LATER THIS EVENING. 
STILL THESE CELLS ARE FAVORABLY ORIENTATED AS WELL TO TRAIN TOWARD
THE WEST ALONG THE BOUNDARY FURTHER COMPLICATING/WETTING THE
GROUND CONDITIONS.  RAIN RATES UP TO 1.5"/HR ARE POSSIBLE THOUGH
SOME LOSS TO LOW LEVEL MOISTENING AND NATURE OF THESE NARROW CORES
MAY LIMIT OVERALL COVERAGE/FLOODING THREAT BUT IS NOT OUT OF THE
REALM OF POSSIBILITY PRIOR TO MAIN FORCING OCCURRING TOWARD 23-01Z
TIME FRAME.

RADAR TRENDS ALSO SUGGEST OUTER BAND/VORT LOBE ACROSS N MS WILL
SUPPORT FURTHER DPVA ASCENT AND ALONG WITH LOWER LEVEL MST
CONVERGENCE ALONG THE BAND...SHALLOW WITH OCCASIONALLY
DEEPER/COLDER EXPANDING TOPS (PER GOES-E IR) WILL BE EXPECT FROM
NE MS INTO NW AL IN THE NEXT HOUR OR SO.  CLOUD BEARING MEAN FLOW
SHOULD DIRECT MOST CELLS DUE NORTH THOUGH RIGHT MOVING SUPERCELLS
MAY DEFLECT EASTWARD...THERE IS STILL SOME POSSIBILITY OF CROSS
TRACK/TRAINING PARTICULARLY ACROSS NW AL WHERE BAND ORIENTATION TO
THE MEAN FLOW IS MORE PARALLEL. TOWARD 00Z DPVA/ASCENT CHANNEL
WILL WILL INTERACT WITH THE AFOREMENTIONED DEFORMATION/WARM
FRONTAL ZONE LEADING TO INCREASED ISENTROPIC ASCENT AND EXPANSION
OF MODERATE TO HVY RAIN SHIELD WITH REMAINING EMBEDDED CONVECTIVE
ELEMENTS. 

RECENT HRRR AND ESRL HRRRV3 DUE TO HIGH FREQUENCY REFRESH HAVE
BEEN QUICKER TO THE  EASTWARD EXPANSION OF CONVECTION CAPABLE OF
FLASH FLOODING. BOTH ARE GENERALLY SUGGESTIVE OF 2-3" TOTALS
THROUGH 00Z MAINLY NORTH INTO CENTRAL TN BUT ISOLATED 4" TOTALS
ARE POSSIBLE.  GIVEN THIS FLASH FLOODING IS CONSIDERED POSSIBLE
THROUGH 00Z (THOUGH BECOMING MORE LIKELY AFTERWARD).

GALLINA

ATTN...WFO...BMX...HUN...MEG...OHX...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   36578714 36568582 36528523 35998521 35398602
            34778634 33738727 34018808 35178812 35658827
            35968913 36428875 36478802