Graphic for MPD #0136

MESOSCALE PRECIPITATION DISCUSSION 0136...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
149 AM EDT SUN APR 23 2017

CORRECTION TO THE SECOND DISCUSSION PARAGRAPH

AREAS AFFECTED...UPPER FL KEYS & PORTIONS OF THE GOLD COAST

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

VALID 230539Z - 231139Z

SUMMARY...A LOW PRESSURE AREA MOVING OUT OF THE NORTHWEST
CARIBBEAN SEA IS SLOWLY INCREASING LOW-LEVEL INFLOW AND
INSTABILITY ACROSS THE REGION.  HOURLY RAIN RATES UP TO 2.25"
COULD LEAD TO HEAVY RAIN ISSUES WITHIN URBAN AREAS.

DISCUSSION...AN AREA OF STRATIFORM RAIN WITH EMBEDDED EFFICIENT
THUNDERSTORMS IS STARTING TO IMPACT THE UPPER KEYS AND PORTIONS OF
SOUTHERNMOST MIAMI-DADE COUNTY. A PAIR OF SHORTWAVES SEEN ON WATER
VAPOR IMAGERY ARE APPROACHING THE AREA FROM THE SOUTHEAST GULF OF
MEXICO AND FL STRAITS, INCREASING DIVERGENCE ALOFT.  PRECIPITABLE
WATER VALUES ARE AROUND 2" PER RECENT GPS DATA AND THE 00Z
SOUNDINGS OUT OF KEY WEST AND SWEETWATER FL.  MUCAPES HAVE BEEN
SLOWLY INCREASING, JUST BEYOND 1000 J/KG PER SPC MESOANALYSES. 
VAD WIND PROFILES SHOW SLOWLY INCREASING INFLOW AT 850 HPA, WITH
20-25 KTS NOTED IN THE AREA, INCLUDING FOWEY ROCKS LIGHT.  THE
850-400 HPA MEAN WINDS ARE LIGHT DUE TO THE WESTERLY WINDS ALOFT
COUNTERING THE LOW-LEVEL EASTERLIES, ONLY 5-10 KTS FROM THE
SOUTHWEST.  BULK SHEAR IN THE 0-6 KM LAYER IS CLOSE TO 25 KTS.

THE MESOSCALE GUIDANCE HAS STRUGGLED SIGNIFICANTLY WITH THIS
ACTIVITY, SO HAVE ATTEMPTED TO USE GFS MASS FIELDS TO AUGMENT THE
RAP, WHICH APPEARS TO HAVE AN UNREALISTIC STALLED MOTION WITH THE
850 HPA REFLECTION OF THE LOW.  INFLOW AT 850 HPA COULD INCREASE
ANOTHER 5-10 KNOTS, WHICH WOULD LEAD TO A BROADER CONVECTIVE
FOOTPRINT.  GFS-BASED GDI VALUES ARE ABOVE 35 IN THIS REGION,
WHICH IMPLIES SCATTERED THUNDERSTORM DEVELOPMENT IS POSSIBLE. 
HOURLY RAIN RATES UP TO 2.25" ARE EXPECTED AS CELLS STRUGGLE TO
MOVE.  SHOULD ORGANIZED CONVECTION DEVELOP, WHICH IS POSSIBLE
CONSIDERING THE BULK SHEAR, IT WOULD TRACK PARALLEL TO THE COAST
AT 15-20 KTS.  HEAVY RAIN ISSUES ARE POSSIBLE IN URBAN AREAS OF
THE GOLD COAST AND FOR THE UPPER KEYS.

ROTH

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

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

LAT...LON   26638020 26578001 26058007 25558011 25138034
            24898059 24748085 24818096 24978110 25278077
            25678056 26148042 26288042 26478033


Last Updated: 149 AM EDT SUN APR 23 2017