MESOSCALE PRECIPITATION DISCUSSION 0128
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 PM EDT SAT MAY 05 2018

AREAS AFFECTED...EASTERN KY...SOUTHERN WV...SOUTHWEST VA

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

VALID 051915Z - 060115Z

SUMMARY...SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE THIS
AFTERNOON. INTENSE RAINFALL RATES TO 1.5 INCHES/HR AND SOME
POSSIBLE REPEATING OF CELLS MAY RESULT IN SOME FLASH FLOOD
CONCERNS.

DISCUSSION...THE LATEST SURFACE ANALYSIS SHOWS A QUASI-STATIONARY
FRONT DRAPED FROM NEAR THE VA/NC BORDER BACK TO THE WEST ACROSS
THE TN VALLEY. THIS FRONT ALONG WITH A WEAK WAVE OF LOW PRESSURE
AND COUPLED WITH A WEAK SHORTWAVE IMPULSE ALOFT EMBEDDED WITHIN
INCREASINGLY DIFFLUENT SOUTHWEST FLOW SHOULD HELP FOCUS AT LEAST
BROKEN COVERAGE OF SHOWERS AND THUNDERSTORMS THROUGH THE AFTERNOON
AND EARLY EVENING ACROSS EASTERN KY...SOUTHERN WV AND SOUTHWEST
VA. AN ADDITIONAL FACILITATOR OF THE CONVECTION WILL BE AT LEAST A
MODEST POOL OF INSTABILITY...AND THE LATEST RAP ANALYSIS DOES
DEPICT MUCAPE VALUES OF 500 TO 1000+ J/KG ACROSS EASTERN
KY...SOUTHERN WV AND SOUTHWEST VA.

OVER THE LAST COUPLE OF HOURS...CONVECTION HAS BEEN DEVELOPING BUT
IS STILL NOT OVERLY ORGANIZED AT THIS POINT. HOWEVER...THE LATEST
HRRR/HRRRX GUIDANCE ALONG WITH THE 12Z ARW/ARW2/NMMB CAM SOLUTIONS
DO INDICATE A LIKELIHOOD FOR THE CONVECTION TO BECOME A BIT MORE
CONCENTRATED NEAR AND JUST NORTH OF THE FRONT AND ALSO OVER THE
HIGHER TERRAIN.

THIS WILL BE AIDED BY SOME ADDITIONAL INSTABILITY POOLING ALONG
THE FRONT AND WITH AID OF AN INCREASINGLY FAVORABLE UPPER JET
STRUCTURE OVER THE CENTRAL APPALACHIANS AHEAD OF A SOUTHERN STREAM
SHORTWAVE TROUGH EXITING THE LOWER/MID MS VALLEY AND APPROACHING
THE TN VALLEY. SOME INCREASE IN SOUTHEAST LOW LEVEL FLOW IS
EXPECTED TOO THROUGH THE AFTERNOON WHICH WILL FOSTER AT LEAST SOME
MODEST OROGRAPHIC SUPPORT OVER THE HIGHER TERRAIN OF ESPECIALLY
SOUTHEAST WV.

THE PWATS ACROSS THE REGION ARE ON THE ORDER OF 1.3 TO 1.4 INCHES
WHICH IS ABOUT 1.5 TO 2 STANDARD DEVIATIONS ABOVE NORMAL. EXPECT
THIS MOISTURE COUPLED WITH THE GRADUAL INCREASE IN INSTABILITY AND
LARGER SCALE ASCENT TO PROMOTE AN INCREASE IN RAINFALL RATES THIS
AFTERNOON THAT MAY REACH 1.5 INCHES/HR.

WHILE THE ANTECEDENT CONDITIONS ARE RATHER DRY...THESE RAINFALL
RATES COUPLED WITH THE POTENTIAL FOR REPEATING CELL ACTIVITY AND
THE PRESENCE OF HIGHER TERRAIN WHICH COULD HELP ENHANCE RUNOFF
WILL SET THE STAGE FOR AT LEAST A LOCALIZED FLASH FLOOD THREAT.

A SPECIAL EXCESSIVE RAINFALL OUTLOOK WILL BE ISSUED TO ALSO
REFLECT AN UPGRADE ACROSS THE THREAT AREA TO A SLIGHT RISK. PLEASE
CONSULT THE LATEST QPFERD FOR MORE DETAILS.

ORRISON

ATTN...WFO...JKL...LWX...MRX...RLX...RNK...

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

LAT...LON   38668035 38617972 38307945 37887957 37538007
            37208089 36978160 36728264 36618337 36658405
            37038419 37538369 38008265 38368160