Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 300830
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
429 AM EDT THU MAR 30 2017

...VALID 12Z THU MAR 30 2017 - 12Z FRI MAR 31 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GSM 35 W 9F2 15 SSE ASD 30 NNE MOB 25 W MAI 35 W TLH AAF
65 SSW AAF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SE MKL 25 ESE HSB 15 SW DEC 25 ESE IKK 35 W AOH 10 SSW MFD
25 E ZZV 20 N I16 ROA 20 SE MTV CLT 15 ESE 27A RYY 10 S TCL
20 SE TUP 45 SE MKL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW BWG 30 ENE HNB 10 W DAY 20 S LHQ 15 S JKL 10 SSE OQT
15 SSW CHA 20 NNW BHM 15 NE 1M4 50 NNE MSL 20 WSW BWG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 N AVL 20 WSW HLX MTV 10 NNE AKH 15 NW GRD 15 W CEU 25 N AVL.


...OH/IN/KY/TN/AL/GA...

THE CYCLONE OVER THE PLAINS WILL MAINTAIN STRENGTH WHILE
PROGRESSING EASTWARD...RESULTING IN A BROAD EXPANSE OF
PRECIPITATION ACROSS THE EASTERN UNITED STATES. HEAVIER SWATHS ARE
ANTICIPATED WITHIN THE BROAD WARM SECTOR ALONG THE IMMEDIATE GULF
COAST...AND STRETCHING BOTH NORTH AND SOUTH OF OF THE MIDDLE
TENNESSEE VALLEY WHERE LOW LEVEL INFLOW / MOISTURE TRANSPORT WILL
BE MAXIMIZED.

WHILE THE LARGE SCALE PRECIPITATION PATTERN IS SIMILAR AMONG THE
MODELS...THERE ARE PLENTY OF DIFFERENCES REGARDING THE DETAILS OF
CONVECTIVE EVOLUTION...WITH BROADLY FAVORABLE SYNOPTICS AND HEIGHT
FALLS EXTENDING DOWN WELL INTO THE GULF...BUT WITH ONLY MARGINALLY
FAVORABLE EARLY-SPRING MOISTURE AND INSTABILITY ALONG MOST OF THE
WARM CONVEYOR BELT FROM JUST INLAND OF THE GULF COAST REGION UP TO
THE OHIO VALLEY. A SITUATION SUCH AS THIS SUPPORTS A BROAD
MARGINAL RISK OF EXCESSIVE RAINFALL. WE DID...HOWEVER...INTRODUCE
A SLIGHT RISK AREA STRETCHING NORTH AND SOUTH OUT OF THE MIDDLE
TENNESSEE VALLEY...WHERE MOISTURE TRANSPORT WILL BE MAXIMIZED
DURING PEAK HEATING AND EARLY EVENING. SOLUTIONS FROM THE MAJORITY
OF THE 00Z HI-RES GUIDANCE CLUSTERS TOGETHER WITH POCKETS OF
HEAVIER RAINFALL IN THIS ZONE...GENERALLY EITHER SIDE OF A LINE
FROM HUNTSVILLE TO CINCINNATI. THERE IS LITTLE SEPARATION BETWEEN
THE MEAN 0-6 KM WIND AND CORFIDI VECTORS FOR FORWARD PROPAGATING
SYSTEMS PER NAM FORECASTS...SUGGESTING GOOD ODDS OF TRAINING CELLS
FROM SSW TO NNE...WHICH IS BORN OUT IN LOOPS OF SIMULATED
REFLECTIVITY / HOURLY QPF FROM SOME OF THE HI-RES MODELS. FLASH
FLOOD GUIDANCE VALUES ARE NOT PARTICULARLY LOW...BUT ARE
ATTAINABLE...AT ABOUT 2 INCHES IN 3 HOURS. PARTS OF NORTHERN
ALABAMA...ESPECIALLY...HAVE SEEN ABOVE AVERAGE PRECIPITATION OVER
THE LAST 7 DAY PERIOD...AND MAY BE MORE SUSCEPTIBLE TO RAPID
RUNOFF.


...UPSLOPE REGIONS OF NC/SC/VA...

MODEL PRECIPITATION OUTPUT HAS ALSO TRENDED QUITE A BIT HEAVIER IN
THE UPSLOPE REGION TO THE LEE SIDE OF THE MOUNTAINS IN WESTERN
NC/SC AND SOUTHWEST VA...WHERE WE INTODUCED A SLIGHT RISK OF
EXCESSIVE RAINFALL. PRECIPITABLE WATER IS SOMEWHAT MARGINAL...BUT
IS SUFFICIENT TO SUPPORT ROBUST CONVECTIVE UPDRAFTS AND HEAVY RAIN
RATES...WITH PW VALUES RISING TO NEAR 1.25 INCHES. OTHERWISE...THE
SETUP IS QUITE FAVORABLE FOR A PROLONGED PERIOD OF
UPSLOPE-ENHANCED PRECIPITATION MAKING LITTLE EASTWARD
PROGRESS...WHILE AWAITING THE SLOWLY APPROACHING LARGE SCALE
WEATHER SYSTEM FROM THE WEST. AGAIN...THE PW VALUES ARE SOMEWHAT
MARGINAL...AND FLASH FLOOD GUIDANCE VALUES ARE ON THE HIGH
SIDE...BUT WE ERRED ON THE SIDE OF CAUTION GIVEN THE VERY
FAVORABLE SYNOPTIC PATTERN AND EVENT TIMING...IN A REGION THAT IS
PRONE TO SLOW MOVING HEAVY RAIN FROM OFTEN SHALLOW CONVECTION THAT
CAN MAKE IT LOOK LESS THREATENING IN SOME DATASETS.

BURKE
$$




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