Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 310031
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
818 PM EDT SUN AUG 30 2015

...VALID 01Z MON AUG 31 2015 - 12Z MON AUG 31 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 E NRB 15 SSE NIP 15 NW VQQ 25 WSW BQK 30 NNW NBC 35 S FLO
30 S MYR 60 SE CHS 70 SE HXD 45 E NRB.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SE BKV 25 SSW BOW 10 SW RSW 25 WSW APF 45 WSW PGD 15 WNW PIE
15 SE BKV.

21-01Z UPDATES...


EXPANDED THE SLIGHT RISK AREA A LITTLE FARTHER NORTH ALONG THE
SOUTH CAROLINA COAST...WHILE ALSO REMOVING THE AREA OVER SOUTH AND
SOUTHEAST FL... BASED ON THE LATEST TRENDS WITH RADAR AND
SATELLITE DATA AS WELL AS SOME OF THE MORE RECENT MESOSCALE
GUIDANCE (INCLUDING BOTH THE HRRR AND EXPERIMENTAL HRRR).
MID-LEVEL FORCING AND CORRESPONDING LOW-LEVEL MOISTURE FLUX
CONVERGENCE IS SLOWLY WEAKENING OVER SOUTH AND SOUTHEAST FL...AS
HAS THE INSTABILITY OVER THE PAST FEW HOURS (MIXED-LAYER CAPES NOW
DOWN TO AROUND 1000-1500 J/KG). OTHERWISE...QUITE A FAVORABLE
THERMODYNAMIC PROFILE WITH A DEEP/NARROW INSTABILITY PROFILE
(MIXED LAYER CAPES 1000-2000 J/KG)...EQUILIBRIUM LEVEL (EL) AROUND
50 KFT...AND WET BULB ZERO LEVELS AOA 15 KFT (DEEP WARM CLOUD
LAYERS). AS A RESULT PW VALUES ARE QUITE HIGH...BETWEEN 2.1-2.4"
OVER THE REMAINING OUTLOOK AREAS. FAVORABLE WARM-RAIN PROCESSES
(HIGHLY EFFICIENT RAINFALL RATES) WILL MAKE FOR SHORT-TERM RUNOFF
ISSUES UNDER THE MORE INTENSE CONVECTIVE CELLS... PARTICULARLY IN
AREAS ALONG THE GA/SC COAST WHERE THE LATEST 1 HOUR (3 HOUR) FFG
HAS DROPPED TO 1.5-2.0 INCHES (2-2.5 INCHES). MEANWHILE...WHAT
CONTINUES TO ALLOW THE MORE WIDESPREAD CONVECTION ALONG THE EAST
COAST OF FL THROUGH GA/SC IS THE FAVORABLE UPPER DIVERGENCE (AND
DIFFLUENCE) E-NE OF THE VIGOROUS MID-UPPER LEVEL VORT CENTER
CURRENTLY PIVOTING ACROSS CENTRAL GA PER THE LATEST WATER VAPOR
IMAGERY. THIS WILL HELP MAINTAIN THE ORGANIZED NUMEROUS-WIDESPREAD
CONVECTION ALONG WITH THE POTENTIAL FOR LOCALIZED EXCESSIVE
RAINFALL RATES WELL INTO THE EVENING HOURS (PAST PEAK DIURNAL
HEATING).

HURLEY


PREVIOUS DISCUSSION FOLLOWS...


...WESTERN FLORIDA COASTAL REGIONS...

WIDESPREAD HEAVY RAINS LIKELY THIS PERIOD ACROSS CENTRAL TO SOUTH
FLORIDA AS MUCH ABOVE AVERAGE PW VALUES WILL CONTINUE TO BE DRAWN
NORTHEASTWARD ON THE SOUTHEAST SIDE OF THE MID TO UPPER LEVEL
CLOSED LOW OVER THE NORTH CENTRAL GULF.   STRENGTHENING
SOUTHEASTERLY TO SOUTHERLY LOW LEVEL FLOW AND FAVORABLE UPPER
DIFFLUENCE TO THE SOUTHEAST OF THE CLOSED LOW AND AHEAD OF ANY LOW
TO MID LEVEL VORTS COMING OUT OF THE TROPICS ASSOCIATED WITH THE
REMNANTS OF ERIKA WILL SUPPORT POTENTIAL FOR WIDESPREAD HEAVY
PRECIP TOTALS IN THIS MUCH ABOVE AVERAGE PW AXIS OVER CENTRAL TO
SOUTH FLORIDA.  WHILE THERE IS A LOT OF QPF DETAIL DIFFERENCES
AMONG THE MODELS---THERE IS A DEFINITE SIGNAL FOR HEAVY TO
ISOLATED URBAN RUNOFF ISSUES ACROSS THE SOUTHEASTERN AND
SOUTHWESTERN COASTAL REGIONS OF FLORIDA---INCLUDING THE KEYS.


...COASTAL SOUTHEAST...

CONCERNS FOR VERY HEAVY TO ISOLATED EXCESSIVE RAINFALL AMOUNTS
ALSO ALONG THE COASTAL SOUTHEAST FROM FAR NORTHEAST FL THROUGH
COASTAL GEORGIA AND MOST OF COASTAL SOUTH CAROLINA.   SEPARATE
FROM ANY REMNANTS OF ERIKA AFFECTING SOUTH FLORIDA---HIGH PW
VALUES AND FAVORABLE UPPER DIFFLUENCE WILL ALSO BE PUSHING
NORTHEASTWARD ON THE EASTERN SIDE OF THE NORTH CENTRAL GULF COAST
UPPER LOW---INTO THE COASTAL SOUTHEAST.  MODELS ARE SHOWING SOME
DIFFERENCES WITH RESPECT TO HOW FAR AND FAST HEAVY PRECIP TOTALS
PUSH NORTHEASTWARD ALONG THE SOUTHEAST COAST.  THERE
IS--HOWEVER---GENERAL AGREEMENT FOR HEAVY TO ISOLATED EXCESSIVE AT
LEAST REACHING COASTAL AREAS OF THE SOUTHEAST---POSSIBLY EXTENDING
FARTHER INLAND.  WPC DID LEAN TOWARD THE FARTHER INLAND HEAVY RAIN
SOLUTIONS OF THE ECMWF---UKMET AND NSSL WRF GIVEN THE STRONG
UPSTREAM CLOSED LOW INITIALLY OVER THE NORTH CENTRAL GULF THAT
WILL BE PRESSING NORTHEASTWARD.

ORAVEC/TERRY
$$





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