266  
AWUS01 KWNH 182113  
FFGMPD  
FLZ000-190230-  
 
MESOSCALE PRECIPITATION DISCUSSION 0111  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
512 PM EDT SUN APR 18 2021  
 
AREAS AFFECTED...NORTHERN FLORIDA PENINSULA...  
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE  
 
VALID 182115Z - 190230Z  
 
SUMMARY...TRAINING CELLS CAPABLE OF 2"+/HR RATES AND SATURATED  
GROUNDS SUPPORT POSSIBLE RAPID INUNDATION/FLASH FLOODING CONCERNS  
THROUGH LATE EVENING HOURS.  
 
DISCUSSION...GOES-E WV SUITE DEPICTS A SOLID SHORTWAVE  
SOUTH-SOUTHEAST OF THE MOUTH OF THE MISSISSIPPI RIVER ADVANCING  
EASTWARD WITH BROAD UPPER LEVEL DIVERGENCE DOWNSTREAM ACROSS THE  
NORTHEASTERN GULF OF MEXICO. AS SUCH, A SURFACE INFLECTION IS  
ENHANCING ALONG AN SW-NE ORIENTED BOUNDARY AND ENHANCING SOUTHERLY  
FLOW ACROSS THE WEST COAST THE PENINSULA WITH 10-15KT FLOW  
STRENGTHENING TO 20-25KTS FROM SURFACE TO 850MB AS THE SHORTWAVE  
APPROACHES. THE FRONTAL ZONE IS DRAPED ACROSS THE PENINSULA FROM  
BKV TO SOUTH OF MCO, NORTH OF VRB ANCHORED BY OUTFLOW FROM EARLIER  
CONVECTIVE OUTFLOW.  
 
WITHIN THE WARM SECTOR, TDS ARE OVER 70F THOUGH 850-7H LPW  
SUGGESTS WESTERN ATLANTIC SOURCE OF DRIER AIR...SO INSTABILITY IS  
SIZABLE WITH MLCAPES OVER 2000 J/KG, SUGGESTING SOME DRY AIR  
ENTRAINMENT MAY RESULT CLOSER/SOUTH OF THE FRONTAL BOUNDARY, BUT  
STILL LOW LEVEL INFLOW WOULD BE VERY MOIST, SO SURFACE BASED CELLS  
WILL HAVE AMPLE ENTRAINMENT TO PRODUCE SOME MOISTURE FLUX  
CONVERGENCE TO SLOWLY SATURATE PROFILES FOR INCREASED RAINFALL  
EFFICIENCY WELL AFTER MATURITY. LPW ALSO DENOTES A MORE DEEPLY  
SATURATED ENVIRONMENT ACROSS THE PANHANDLE AND FAR NORTHERN  
FLORIDA WITH DEEPEST MOISTURE OF 1.75 TO 2" ALONG THE FRONTAL  
ZONE/INVERTED SURFACE TROF AXIS ALONG/AHEAD OF SHORTWAVE  
HEIGHT-FALLS. DEEP UNIDIRECTIONAL FLOW NORTH OF THE SURFACE  
BOUNDARY ALONG THE 850MB TROF AXIS WOULD HAVE GREATER MOISTURE  
AVAILABILITY THOUGH INSTABILITY WOULD HAVE SIZABLE REDUCTION  
GIVEN THE NARROWER PROFILES WITH AT MOST MUCAPE OF 1000-1250 J/KG.  
AS SUCH, A NARROW AXIS FROM LEVY/CITRUS COUNTY TO FLAGLER/N  
VOLUSIA COUNTY WOULD BE THE INTERSECTION OF BEST INSTABILITY AND  
MOISTURE. STRONG CONVECTIVE CORES ALONG THIS AXIS WILL HAVE THE  
CAPABILITY OF PRODUCING QUICK BURST (1.25"/15MINS PER HRRR) RATES,  
PARTICULARLY AS BEST FORCING AND MATURITY OF CONVECTIVE  
DEVELOPMENT OCCURS NEARER TO 23-00Z ALONG/NEAR NW FLORIDA COAST.  
 
CELLS SHOULD BE QUICK MOVING BUT HAVE A TRAINING ORIENTATION  
RESULTING IN RAINFALL TOTALS OF 2-3" ARE POSSIBLE BUT COULD EVEN  
REACH 4" IN VERY ISOLATED LOCATIONS THROUGH 03Z. IF THE TRAINING  
AXIS REMAINS FAIRLY STABLE, WHICH CURRENT TRENDS SUGGEST GIVEN  
AMPLITUDE OF THE WAVE APPROACHING, THE AXIS OF HEAVIEST RAINFALL  
MAY TRACK THROUGH AREAS SATURATED LATE LAST EVENING WITH 2-3" FROM  
MARION TO FLAGLER COUNTY,RESULTING IN AREA OF GREATEST RISK FOR  
RAPID INUNDATION/FLASH FLOODING.  
 
SOME DRY AIR ENTRAINMENT COULD RESULT IN COLD POOLS THAT COULD SAG  
THE AXIS SOUTH, WHERE GROUND CONDITIONS ARE A BIT BETTER BUT AHPS  
WEEKLY ANOMALIES ARE WELL OVER 300% OF NORMAL. NASA SPORT SOIL  
SATURATION THROUGH 0-40 CM ARE FULLY SATURATED ACROSS THE  
PANHANDLE INTO NORTHERN FLORIDA (OVER 98%) WHILE BELOW 70% ACROSS  
THE I-4 CORRIDOR, THOUGH HAS GREATER URBAN SETTINGS AND MORE  
HYDROPHOBIC HIGH-RUNOFF CAPABILITY. AS SUCH, HAVE ENCOMPASSES  
THESE AREAS INTO THE AREA OF CONCERN.  
 
GALLINA  
   
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...JAX...MLB...TAE...TBW...  
 
ATTN...RFC...SERFC...NWC...  
 
LAT...LON 30108184 30018122 29288088 28168041 28028106  
28158203 28328281 28598287 28888288 29438334  
29868352 30058258  
 
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