MESOSCALE PRECIPITATION DISCUSSION 0405
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
902 AM EDT THU JUL 05 2018

AREAS AFFECTED...WRN PA...ERN OH...NRN WV PANHANDLE

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 051301Z - 051700Z

SUMMARY...SLOW-MOVING THUNDERSTORMS ARE EXPECTED TO CONTINUE IN A
SCATTERED FASHION OVER WESTERN PENNSYLVANIA AND ADJACENT AREAS
THIS MORNING. THESE STORMS MAY PRODUCE AROUND 2-3 INCHES OF RAIN
IN AN HOUR IF THEY CAN MAINTAIN IN A FOCUSED AREA FOR THAT AMOUNT
OF TIME...WHICH WOULD LIKELY PRODUCE FLASH FLOODING.

DISCUSSION...KPBZ RADAR SHOWS SLOW-MOVING CONVECTION IN FAR
WESTERN PENNSYLVANIA THIS MORNING. THE 12Z SOUNDING FROM KPIT WAS
ALREADY QUITE UNSTABLE...WITH OVER 2000 J/KG OF AVAILABLE CAPE FOR
A PARCEL SOURCE LAYER AROUND 900-850MB. THE 2.05 INCH PWAT WAS
NEAR THE UPPER ECHELON OF THE OBSERVED SOUNDING RECORD AT THAT
SITE...AND ANALYSIS OF THE INITIAL MODEL STATES SHOWS A BROAD AREA
OF PWATS AROUND OR ABOVE THE 99TH PERCENTILE IN THE REGION. THE
SOUNDING...AND REGIONAL RADAR VWPS...SHOW A BROAD AREA OF WESTERLY
FLOW AROUND 900-850MB AROUND 10-15 KNOTS IN MAGNITUDE. THIS WOULD
BE SUFFICIENT TO ENABLE STORM ORGANIZATION AND PERHAPS ALLOW FOR
SOME BACKBUILDING TOWARD A REGION OF GREATER INSTABILITY IN
EASTERN OHIO. THIS APPEARS TO BE HAPPENING WITH SOME OF THE SMALL
CLUSTERS OF CONVECTION ON THE KPBZ RADAR. THEREFORE...A
COMBINATION OF BACKBUILDING AND OVERALL SLOW STORM MOTION (NEAR
THE AXIS OF A MID-UPPER LEVEL RIDGE) SHOULD CONTINUE THROUGH THE
MORNING HOURS.

GIVEN THE SLOW STORM MOTIONS AND VERY MOIST AND UNSTABLE
ATMOSPHERE...VERY HEAVY RAIN RATES WILL BE POSSIBLE AND CONVECTION
SHOULD BE VERY EFFICIENT AT RAINFALL PRODUCTION. MRMS AND KPBZ
DUAL POL HAVE ALREADY ESTIMATED SOME RAIN RATES AS HIGH AS 2-3
IN/HR IN SOME LOCATIONS. THESE WOULD REACH AROUND 200 PERCENT OR
MORE OF FLASH FLOOD GUIDANCE IN SOME AREAS...AND BE VERY LIKELY TO
PRODUCE FLASH FLOODING.

LAMERS

ATTN...WFO...BUF...CLE...CTP...ILN...PBZ...RLX...

ATTN...RFC...MARFC...NERFC...OHRFC...

LAT...LON   42068008 41857769 41027747 39957905 39508097
            39698221 40538227 41518168