MESOSCALE PRECIPITATION DISCUSSION 0304
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
700 AM EDT TUE JUN 06 2017

AREAS AFFECTED...SOUTHERN FL PENINSULA/UPPER KEYS

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

VALID 061100Z - 061600Z

SUMMARY...ORGANIZED CONVECTION CONTINUES MOVING EAST AT ~10 KTS
ACROSS SOUTHWEST FL.  HOURLY RAIN RATES TO 3" ARE EXPECTED, BUT
FORWARD PROPAGATION COULD START IN EARNEST SHORTLY WHICH COULD
LIMIT OVERALL TOTALS TO LOCAL 3-5" AMOUNTS.

DISCUSSION...A WEAK WARM FRONT IS LOCATED IN THE THERMAL FIELD
ACROSS THE SOUTHERN EVERGLADES AT 10Z.  ALOFT, THE FLOW IS QUITE
DIVERGENT BETWEEN THE SUBTROPICAL STREAM AND THE SOUTHERN STREAM
OF THE POLAR JET TO THE EAST-SOUTHEAST OF AN UPPER LOW.  INFLOW AT
850 HPA IS SLIGHTLY CONVERGENT OUT OF THE SOUTHWEST NEAR 30 KTS
INTO THE REGION.  INSTABILITY NEAR THE CONVECTION HAS BEEN
LOWERING DUE TO ITS PRESENCE, WHILE IT REMAINS SIGNIFICANT TO ITS
EAST -- IN THE RANGE OF 2000-4000 J/KG WHICH IS LEADING TO MINIMAL
ELEVATION OVER THE BOUNDARY.

EVEN THOUGH MINIMAL THICKNESS GRADIENT EXISTS ACROSS THE REGION IN
THE PROXIMITY OF THE SUBTROPICAL JET, THE EXPECTATION IS FOR THE
FORWARD PROPAGATION TO PICK UP STEAM OVER THE NEXT SEVERAL HOURS
CAUSED BY THE EVOLVING INSTABILITY FIELD, WHICH SHOULD SLOWLY
LOWER THE SHORT TERM HEAVY RAINFALL RISK.  HOWEVER, DECREASING CIN
NEAR THE SURFACE BOUNDARY OVER THE NEXT FEW HOURS COULD LEAD TO
NEW CONVECTION CLOSER TO THE GOLD COAST AND UPPER KEYS WITH TIME. 
EVEN THOUGH UPSTREAM CONVECTION IN THE GULF IS EXPECTED TO
CONTINUE DUE TO PERSISTENT 850 HPA INFLOW THAT IS NOT FORECAST TO
WANE, THE MOTION VECTOR SHOULD BECOME MORE EAST-SOUTHEAST TO
SOUTHEAST WITH TIME DUE TO CHANGES IN THE INSTABILITY FIELD/A
STALLING OF THE FRONTAL BOUNDARY -- PERHAPS IN THE FORM OF A WAVY
SQUALL LINE -- SLOWLY INCREASING THE THREAT TO PLACES SUCH AS
FLORIDA CITY SHOULD TRAINING CHARACTERISTICS FORM IN ITS SOUTHWEST
FLANK.  A SOUTHWARD ADJUSTED 09Z HRRR/06Z HRRR EXPERIMENTAL
APPEARS TO HAVE THE BEST CONVECTIVE IDEA HERE.  AVAILABLE MOISTURE
AND INSTABILITY SUPPORT HOURLY RAIN RATES TO 3".  BELIEVE LOCAL
MAXIMA OF 3-5" ARE POSSIBLE HERE AS THE CONVECTION ATTEMPTS TO
TURN EAST TO SOUTHEAST AT SLIGHTLY FASTER FORWARD SPEED.  WHILE
THIS WOULD BE AN ISSUE FOR URBAN AREAS, IT WOULD HELP RELIEVE DRY
SEASON-INDUCED DROUGHT ACROSS THE EVERGLADES.

ROTH

ATTN...WFO...KEY...MFL...

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

LAT...LON   26478086 26428008 25938006 25298027 24948051
            24888090 25158123 25508131 25908178 26038181
            26078128