MESOSCALE PRECIPITATION DISCUSSION 0270
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 PM EDT THU JUN 07 2018

AREAS AFFECTED...SOUTHERN FL

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

VALID 071810Z - 080010Z

SUMMARY...HEAVY SHOWERS AND THUNDERSTORMS TO BECOME MORE NUMEROUS
THIS AFTERNOON AND THROUGH THE EARLY EVENING HOURS. SOME FLOODING
WILL BE POSSIBLE.

DISCUSSION...STRONG DIURNAL HEATING EARLY THIS AFTERNOON HAS
ALREADY CONTRIBUTED TO AS MUCH AS 2000+ J/KG OF MLCAPE ACROSS
SOUTHEAST FL...AND THIS COUPLED WITH AT LEAST MODEST LOW LEVEL
CONVERGENCE AIDED BY SEABREEZE ACTIVITY HAS BEEN FACILITATING
CONVECTIVE INITIATION OVER THE LAST 1 TO 2 HOURS SOUTH OF LAKE
OKEECHOBEE AND ALONG ADJACENT AREAS JUST INLAND FROM THE SOUTHEAST
FL COASTLINE. THE LATEST GOES-16 VISIBLE AND CLEAN IR IMAGERY
CONFIRM THIS AND ARE SHOWING AN INCREASED DEGREE OF ORGANIZATION
WITH TIME.

THE LAST SEVERAL RUNS OF THE HRRR AND HRRRX GUIDANCE HAS BEEN
SHOWING A RATHER STRONG SIGNAL FOR VERY HEAVY AND SLOW-MOVING
SHOWERS AND THUNDERSTORMS THIS AFTERNOON ACROSS A RATHER LARGE
AREA OF SOUTHERN FL...BUT ESPECIALLY TOWARD THE ATLANTIC SIDE OF
THE PENINSULA WHERE LOW LEVEL CONVERGENCE IS EXPECTED TO BE
RELATIVELY MAXIMIZED. AN ADDITIONAL FACTOR IN DRIVING CONVECTION
THIS AFTERNOON WILL BE THE PROXIMITY OF AN UPPER LOW OVER THE
NORTHEAST GULF OF MEXICO WHICH IS PROVIDING AT LEAST SOME MODEST
UPPER LEVEL DIVERGENCE OVER THE PENINSULA. THERE IS ALSO EVIDENCE
OF A SMALL SCALE SHORTWAVE TROUGH OVER SOUTHWEST FL WHICH IS
SHOWING UP IN GOES-16 WV IMAGERY.

THE HRRR/HRRRX GUIDANCE ALONG WITH THE 12Z ARW/NMMB SOLUTIONS
SUPPORT AS MUCH AS 4 TO 6+ INCHES OF RAIN...AND THIS SEEMS
PLAUSIBLE GIVEN PWATS OF 1.7 TO 1.9 INCHES AND THE EXPECTATION OF
SLOW CELL MOTIONS GIVEN RATHER WEAK MID LEVEL STEERING FLOW. THE
THREAT SHOULD PERSIST THROUGH ABOUT 00Z...WITH CONVECTION THEN
WANING THEREAFTER AS DIURNAL HEATING DIMINISHES. GIVEN THE
EXPECTED RAINFALL AMOUNTS...SOME RUNOFF PROBLEMS AND/OR FLOODING
WILL BE POSSIBLE PRIOR TO 00Z.

ORRISON

ATTN...WFO...MFL...MLB...

ATTN...RFC...SERFC...

LAT...LON   27818048 27478017 26627994 26137996 25648013
            25448041 25438071 25658097 25938107 26508086
            27028082 27588080