MESOSCALE PRECIPITATION DISCUSSION 0469
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
846 PM EDT MON JUL 16 2018

AREAS AFFECTED...NERN OH...NRN PA...WRN/CTRL NY

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

VALID 170043Z - 170630Z

SUMMARY...SCATTERED THUNDERSTORMS WERE DEVELOPING AHEAD OF AN
ADVANCING COLD FRONT IN THE EASTERN GREAT LAKES. THESE STORMS WERE
MERGING INTO SMALL CLUSTERS AND COULD TRAIN TO PRODUCE LOCALLY
HEAVY SWATHS OF RAINFALL. RAIN RATES OF 1-2 IN/HR WILL BE COMMON
WITH THE STRONGER STORMS...AND IF TRAINING CAN OCCUR FLASH
FLOODING WOULD BE POSSIBLE.

DISCUSSION...REGIONAL RADARS AND GOES-16 IR SATELLITE CHANNELS
SHOWED SCATTERED CONVECTION ACROSS THE EASTERN GREAT LAKES REGION
GRADUALLY INCREASING IN AREAL EXTENT AND INTENSITY. ALTHOUGH A
CONTINUOUS BAND OF THUNDERSTORMS HAD NOT DEVELOPED... CONVECTION
WAS BEGINNING TO ORGANIZE INTO SMALL-MEDIUM SIZED CLUSTERS...
PARTICULARLY IN AREAS OF ENHANCED CONVERGENCE (SUCH AS THE SOUTH
SHORE OF LAKE ERIE). ENOUGH OF THESE CLUSTERS WERE BECOMING
SUFFICIENTLY ALIGNED IN THE DEEP LAYER MEAN WIND TO MAKE A COUPLE
HOURS OF TRAINING CONVECTION A MORE PLAUSIBLE SCENARIO THIS
EVENING. ONE SUCH EXAMPLE HAS ALREADY OCCURRED TO THE WEST OF
ELMIRA NY ALONG THE NY-PA BORDER. PERSISTENCE OF 1-2 IN/HR RAIN
RATES FOR A COUPLE HOURS VIA TRAINING CONVECTION SHOULD MAKE FLASH
FLOODING A POSSIBILITY ACROSS THE REGION.

THE AIR MASS IN FRONT OF THE COLD FRONT WAS RELATIVELY HOMOGENEOUS
WITH MODERATE INSTABILITY (RAP MODEL ANALYSIS MLCAPE 1000-2000
J/KG) AND ELEVATED PRECIPITABLE WATER VALUES (1.7 TO 1.9 INCHES;
ABOVE THE 90TH PERCENTILE). EFFECTIVE DEEP LAYER SHEAR WAS ALSO
AROUND 25-30 KNOTS...SO THE ENVIRONMENT IS OVERALL SUPPORTIVE OF
ORGANIZED CLUSTERS AND LINES OF STORMS THAT COULD BE EFFICIENT
RAINFALL PRODUCERS. GIVEN THAT THE SURFACE COLD FRONT IS STILL
UPSTREAM AND MODERATE INSTABILITY SHOULD PERSIST THROUGH THE
EVENING... THE THREAT OF FLASH FLOODING SHOULD CONTINUE OVER THE
NEXT SEVERAL HOURS.

LAMERS

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

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

LAT...LON   43717690 43607504 42887453 41767673 41007914
            40728128 41058233 41678197 42658008 43407874