MESOSCALE PRECIPITATION DISCUSSION 0399
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
859 AM EDT WED JUL 04 2018

AREAS AFFECTED...NORTHWEST PA & SOUTHERN TIER OF NY

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

VALID 041259Z - 041859Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE GROWING IN COVERAGE NEAR A
STATIONARY FRONT.  WITHIN THE PULSE CONVECTION, HOURLY RAIN TOTALS
TO 2" WITH LOCAL AMOUNTS OF 3" ARE POSSIBLE.

DISCUSSION...A POSITIVELY TILTED SHORTWAVE EXTENDING
WEST-SOUTHWEST FROM NORTHERN NY INTO LAKES ONTARIO AND ERIE NOTED
ON WATER VAPOR IMAGERY AS AN AREA OF UPPER LEVEL DRYING AND A WEAK
850 HPA LOW WEST OF BUFFALO APPEAR TO HAVE BEEN SUFFICIENT TO LEAD
TO A RECENT UPTICK IN BOTH MU CAPE VALUES AND CONVECTIVE COVERAGE
NEAR THE WESTERN PA/NY BORDER NEAR A WAVY STATIONARY BOUNDARY.  A
RECENT SOUNDING FROM BUFFALO INDICATES ~1400 J/KG OF SURFACE-BASED
CAPE, WHICH IS A RATHER GOOD MATCH TO SPC MESOANALYSES.  FLOW IN
THE LOW- TO MID-LEVELS IS WEAK DUE TO THE PROXIMITY OF A LOW- TO
MID-LEVEL RIDGE, WHICH IS LEADING TO A PULSE CHARACTER TO THE
MORNING CONVECTION.  INFLOW IS WEAK OUT OF THE WEST-SOUTHWEST AT
10 KTS.

THE MESOSCALE GUIDANCE IS STRUGGLING HERE, THOUGH THERE WAS SOME
SIGNAL FOR 1"+ AN HOUR RAIN TOTALS WITHIN THE HREF MEMBERS THROUGH
15Z BEFORE CIN ERODES.  FROM 16Z ONWARD, SURFACE-BASED CONVECTION
IS EXPECTED TO TAKE OVER NEAR THE PA/NY BORDER AS THE BASE OF THE
WEAK UPPER LEVEL SHORTWAVE MOVES IN FROM THE WEST WHICH SHOULD
LEAD TO ANOTHER ROUND OF PULSE CONVECTION.  THE 06Z NAM CONEST AND
RECENT EXPERIMENTAL HRRR RUNS WERE MISSING THE BOAT ON THE CURRENT
ACTIVITY, WHILE OPERATIONAL HRRR AND 06Z CANADIAN RUNS HAD A
BETTER GRASP ON THE SITUATION.  ALONG WITH THE BORDERLAND, THE
GUIDANCE HAS A SIGNAL FOR AFTERNOON CONVECTION WITH HEAVY RAINFALL
IN WESTERN PA BY 19Z.  HOURLY RAIN TOTALS TO 2" WITH LOCAL AMOUNTS
TO 3" ARE ANTICIPATED, WHICH COULD LEAD TO LOCALIZED ISSUES.

ROTH

ATTN...WFO...BGM...BUF...CLE...CTP...PBZ...

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

LAT...LON   42717880 42497478 41457583 41647745 40927893
            41098039 42068064