MESOSCALE PRECIPITATION DISCUSSION 0247
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 PM EDT SAT MAY 20 2017

AREAS AFFECTED...UPPER OH VALLEY & CENTRAL APPALACHIANS

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

VALID 201836Z - 210036Z

SUMMARY...CONVECTION IS DEVELOPING OVER PARTIALLY SATURATED SOILS.
 FLASH FLOODING IS A CONCERN.

DISCUSSION...A CONVECTIVE SHORTWAVE MOVING THROUGH INDIANA
COMBINED WITH DAYTIME HEATING HAS LED TO SURFACE BASED CONVECTION
TO ITS SOUTH ACROSS NORTHERN KY.  BULK SHEAR IN THE 0-6 KM LAYER
IS CLOSE TO 30 KTS PER SPC MESOANALYSES.  TO THE EAST, PULSE
CONVECTION ACROSS SOUTHWEST VA HAS BEEN EFFICIENT LOCALLY, WITH
HOURLY RAIN RATES UP TO 2".  PRECIPITABLE WATER VALUES OF 1-1.75"
EXIST ACROSS THE REGION, WITH LOWER VALUES IN HIGHER TERRAIN. 
LOW-LEVEL INFLOW IS STRONGEST ACROSS THE WESTERN PORTION OF THE
AREA, OUT OF THE SOUTHWEST AT 25 KTS PER VAD WIND PROFILES. 
UPSTREAM MLCAPES ACROSS PORTIONS OF KY, WV, AND WESTERNMOST VA ARE
IN THE 1000-2000 J/KG RANGE.

WITH TIME, INFLOW AT 850 HPA INCREASES ACROSS THE UPPER OHIO
VALLEY, SOUTHERN WV AND SOUTHWEST VA AS A CONVECTIVE SHORTWAVE
APPROACHES.  THE 12Z GFS-BASED GALVEZ-DAVISON INSTABILITY INDEX
SHOWS RISING VALUES ACROSS THE REGION THROUGH 21Z, PEAKING IN THE
30-35 RANGE, WHICH IMPLIES INCREASING CONVECTIVE COVERAGE WITH
TIME.  HOURLY RAIN RATES UP TO 2" ARE SUPPORTED BY THE AVAILABLE
INSTABILITY AND MOISTURE.  THE 850-400 HPA MEAN WINDS AND FORWARD
PROPAGATING CONVECTIVE VECTORS APPEAR TO BE LIGHT HERE, WHICH
INCREASES THE RISK FOR HEAVY RAINS.  THE GUIDANCE SHOWS A SPLOTCHY
RAINFALL PATTERN IN THIS REGION DUE TO A MIX OF ORGANIZED AND
PULSE CONVECTION ANTICIPATED, WITH LOCAL AMOUNTS OF 2-3" INDICATED
THROUGH 00Z.  THE 06Z SSEO NEIGHBORHOOD PROBABILITIES OF EXCEEDING
THE THREE HOUR FLASH FLOOD GUIDANCE THROUGH 00Z SHOW INTERMITTENT
50%+ EXCEEDANCE BETWEEN NORTHERN KY AND SOUTHWEST VA, WHICH IS
CAUSED MAINLY BY LOW FLASH FLOOD GUDIANCE VALUES/PARTIALLY
SATURATED SOILS CAUSED BY A WET 30 DAY PERIOD PARTICULARLY ACROSS
SOUTHERN WV AND SOUTHWEST VA.  FLASH FLOODING IS CONSIDERED
POSSIBLE.

ROTH

ATTN...WFO...AKQ...ILN...JKL...LMK...LWX...MRX...RAH...RLX...
RNK...

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

LAT...LON   39148465 39038243 39058078 38837992 38387918
            37337933 36777872 36387840 36247969 36398161
            37348292 37778362 38588550