Graphic for MPD #0909

MESOSCALE PRECIPITATION DISCUSSION 0909
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EDT MON OCT 23 2017

AREAS AFFECTED...SOUTHERN & CENTRAL APPALACHIANS

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

VALID 231754Z - 232354Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE EXPECTED TO SPREAD UP
TOWARDS THE CENTRAL APPALACHIANS WITH TIME.  HOURLY RAIN TOTALS UP
TO

DISCUSSION...AN UPPER LOW MOVING ACROSS SOUTHERN TN IS EMBEDDED
WITHIN A NEGATIVELY TILTED TROUGH WHICH IS LEADING TO SIGNIFICANT
DIVERGENCE ALOFT ACROSS THE REGION.  ALONG WITH INCREASING
INSTABILITY ACROSS SC, THUNDERSTORMS HAVE BEEN INCREASING IN
NUMBER ACROSS THE WESTERN CAROLINAS.  RADAR ESTIMATES AND
MESOSCALE OBSERVATIONS HAVE SAMPLED HOURLY RAIN TOTALS TO JUST
ABOVE 1" IN THE RECENT ACTIVITY IN SOUTHWEST NC.  PRECIPITABLE
WATER VALUES ARE 1.75-2" PER GPS VALUES -- UP TO THREE SIGMAS
ABOVE LATE OCTOBER AVERAGES.  INFLOW AT 850 HPA IS CONVERGENT AT
35-50 KTS PER VAD WIND PROFILES, NEAR THE MAGNITUDE OF THE MEAN
850-400 HPA WIND.

BASED ON CURRENT VISIBLE NON-OPERATIONAL GOES-16 VEGGIE BAND
IMAGERY SHOWING BREAKS IN THE CLOUD COVER, INSTABILITY SHOULD
BUILD WITHIN THE PIEDMONT OVER THE NEXT FEW HOURS FROM CENTRAL NC
UP INTO CENTRAL VA.  BOUNDARY LAYER CONVERGENCE IS FORECAST TO
INCREASE AHEAD OF THE NORTHWARD MOVING LOW ACROSS THE WESTERN
CAROLINAS INTO SOUTHWEST VA, WHICH SHOULD HOLD UP CONVECTIVE
PROGRESS IN SOUTHWEST VA AND WV.  RAP GUIDANCE HAS BEEN STRUGGLING
TO CATCH UP TO THE INSTABILITY PRESENT OVER ITS PAST SEVERAL RUNS.
 HOURLY RAIN RATES TO 1.25" ARE POSSIBLE.  THE MESOSCALE GUIDANCE
HAS A STRONG SIGNAL FOR LOCAL AMOUNTS UP TO 4".  WHEN COMBINED
WITH THIS MORNING'S RAINFALL, THIS COULD LEAD TO HEAVY
RAIN-RELATED ISSUES IN RUGGED TOPOGRAPHY AND URBAN AREAS FROM THE
WESTERN CAROLINAS INTO WEST VIRGINIA.

ROTH

ATTN...WFO...CAE...GSP...JKL...LWX...MRX...PBZ...RAH...RLX...
RNK...

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

LAT...LON   39358091 39317992 37807921 35808001 34418171
            34738280 36438276 38028216


Last Updated: 154 PM EDT MON OCT 23 2017