Quantitative Precipitation Forecast
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FOUS30 KWBC 290846
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
446 AM EDT SAT APR 29 2017

...VALID 12Z SAT APR 29 2017 - 12Z SUN APR 30 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
BMQ 25 WSW MWL 10 NNW F05 15 NW JWG 10 NE TOP 10 SW MSN LDM
20 WNW OSC BAX PTK 15 NNE FDY 10 NNW VTA 25 NNW CKB 10 SE W22
10 SSE CRW 20 N HOP 30 SSE UTA 30 SE ESF 25 NNE KCMB 20 ENE KXIH
20 E IAH DWH 25 E HYI BMQ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ENE IRK BUU 30 NW MKG 15 W MOP 25 NE GRR 10 N AZO 10 S ASW
10 NW DAY 20 NW UNI 25 E PKB 25 WNW 48I 15 SSE SDF 15 ESE M30
35 ESE SGT 25 SSE BAD 30 WNW UTS 30 NNW LHB 10 NW TKI 10 WNW FSI
15 NNW GOK 20 WNW SZL 30 ENE IRK.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NNE JLN 10 E PPQ 15 SSE AAA 10 SSE MTO 10 WNW HSB 20 N BYH
15 NE SGT 40 ENE TXK 15 NE PRX 20 SSE CHK 30 WNW RVS 15 SSE CFV
30 NNE JLN.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSE VIH 10 W FAM 30 WNW CGI 25 SSW POF 10 WSW SRC 20 WSW MWT
45 SE MLC 20 N MLC 20 NNW MKO 25 ENE GMJ 30 SSE VIH.


...HIGH RISK AND TREMENDOUS RAIN/FLOOD EVENT EXPECTED IN EASTERN
OKLAHOMA / NORTHERN ARKANSAS / SOUTHERN MISSOURI...

ALL THE INGREDIENTS ARE MAXIMIZED. A 3.5 STANDARD DEVIATION UPPER
LOW WITHIN A STRONGLY BUCKLING LARGE SCALE FLOW PATTERN / COUPLED
JET STRUCTURE...HEADING INTO A LENGTHY STALLED FRONTAL ZONE WITH
MOISTURE AND INSTABILITY CHARACTERISTIC OF MID SPRING. FLOW OFF
THE GULF...ORIGINATING IN THE CARIBBEAN...IS UNUSUALLY
STRONG...SQUEEZED BY A 1032 MB HIGH OVER THE WESTERN ATLANTIC. THE
ENSEMBLE SITUATION AWARENESS INFORMATION BASED ON THE NAEFS HAS AN
AWFUL LOT OF 99TH PERCENTILE AND MAX VALUES FOR INTEGRATED VAPOR
TRANSPORT WITHIN THE CONVEYOR BELT FROM EAST TEXAS UP THROUGH
EASTERN OK / WESTERN AR AND INTO MISSOURI. AMPLIFICATION OF THE
LARGE SCALE SYNOPTIC SYSTEM WILL ALSO RETARD EASTWARD
PROGRESSION...RESULTING IN VERY INTENSE AND PERSISTENT RAINFALL
THIS AFTERNOON AND EVENING...WHICH WE SUSPECT WILL BE CENTERED
AROUND NORTHWEST ARKANSAS BASED ON OBSERVATIONAL AND MODEL TRENDS.
THE LOCATION OF THE HEAVIEST RAIN VARIES BETWEEN MODELS...BUT
WITHIN THE WARM CONVEYOR BELT THEY ALL...GLOBAL AND HI-RES MODELS
ALIKE...HAVE A SIGNAL FOR WIDESPREAD 5-PLUS INCH RAINS WITH
EMBEDDED 7 TO 10 INCH AMOUNTS. A FURTHER CONCERN IS THE BREADTH OF
THE 5-PLUS INCH RAINFALL...WHICH MAY AFFECT PARTS OF THREE
STATES...COVERING A LOT OF TERRITORY...RESULTING IN A LARGE VOLUME
OF WATER INTO CERTAIN WATERSHEDS.

AS PRECIPITABLE WATER INCREASES TO NEAR 1.75 INCHES...AND 2.5
STANDARD DEVIATIONS ABOVE AVERAGE FOR LATE APRIL...EXPECT HOURLY
RAIN RATES TO PUSH ABOVE 3 INCHES GIVEN THE HIGH LIKELIHOOD OF
TRAINING. THE EVENT IS EXPECTED TO PEAK THIS AFTERNOON AND EVENING
AS THE LARGE SCALE SYSTEM REACHES MATURITY AND FLOW BECOMES VERY
MERIDIONAL DURING PEAK HEATING / PEAK INSTABILITY. THE HEAVIEST
RAIN IS FORECAST IN AREAS THAT ARE NOT ONLY PRONE TO FLASH
FLOODING DUE TO TERRAIN...BUT ARE ALSO WET FROM ANTECEDENT HEAVY
RAIN EARLIER IN THE WEEK AND RAIN ALREADY OCCURRING EARLY SATURDAY
MORNING. THUS...LIFE-THREATENING CONDITIONS MAY BECOME COMMON
LATER TODAY AND TONIGHT WITHIN THE HIGH RISK AREA.

MODERATE RISK EXTENDS A LITTLE DEEPER INTO EASTERN AND SOUTHERN
OKLAHOMA...AND UP ACROSS SAINT LOUIS TO ILLINOIS...WHERE EXTREME
RAIN TOTALS ARE LESS LIKELY...BUT AVERAGE RAINFALL OF AT LEAST 2
TO 5 INCHES IS FORECAST...INCLUDING VERY HEAVY SHORT TERM RATES.
THE GROUND IN SOME OF THESE AREAS ARE ALSO WET FROM PRIOR RAINFALL.


...MIDWEST AND OHIO VALLEY...

THE FORECAST CARRIES MORE UNCERTAINTY FROM NORTHERN MISSOURI
EASTWARD AND NORTHEASTWARD. THE INITIAL SURGE OF GULF MOISTURE HAD
RELEASED AN EXTENSIVE LINE OF CONVECTION STRETCHING EAST INTO THE
APPALACHIANS...WITH PLENTY OF TRAINING AND FLASH FLOOD CONCERNS.
THIS MAY PERSIST THROUGH LATE MORNING PER CONSISTENCY IN THE HRRR
RUNS. SYNOPTIC FORCING THEN REGROUPS BACK OVER THE MIDWEST AND
LOWER GREAT LAKES. THE MAIN INHIBITING FACTOR COULD BE EXTENSIVE
CONVECTION EXPECTED IN THE SOUTHERN PLAINS AND LOWER MISSOURI
VALLEY THIS MORNING. THIS MAY LIMIT INSTABILITY FARTHER
NORTH...SUCH AS DEPICTED IN THE NAM CONUS NEST AND NCEP
WRF-ARW...WHICH FORECAST MORE TOLERABLE RAINFALL TOTALS FROM SAINT
LOUIS NORTH AND EASTWARD. GIVEN SUCH A DYNAMIC UPPER
SYSTEM...HOWEVER...WITH STRONG WIND FIELDS...IT WOULD NOT TAKE
MUCH OF A BREAK IN THE ACTION TO THEN ALLOW A RAPID NORTHWARD
TRANSPORT OF MOISTURE AND INSTABILITY INTO AREAS WHERE THE HIGHLY
AMPLIFIED JET CIRCULATION WILL BEGIN TO PRODUCE DEEP LIFT FROM
EASTERN MISSOURI TO SOUTHEAST WISCONSIN AND WESTERN
MICHIGAN...ACROSS CHICAGOLAND. PLAYING THE
PROBABILITIES...MODERATE RISK OF EXCESSIVE RAINFALL EXTENDS
THROUGH SAINT LOUIS TO CENTRAL ILLINOIS...WITH SLIGHT RISK FARTHER
NORTH AND EAST.


...TEXAS AND LOUISIANA...

STRONG DEEP LAYER FORCING WILL BE REQUIRED TO OVERCOME THE CAPPING
INVERSION HERE...LIKELY RESULTING IN A NARROW AND MORE PROGRESSIVE
LINE OF CONVECTION. EXTREME TOTALS ARE UNLIKELY...BUT VERY HEAVY
SHORT TERM RAIN RATES MAY CAUSE FLASH FLOODING THIS AFTERNOON AND
OVERNIGHT.


BURKE
$$




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