Quantitative Precipitation Forecast
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FOUS30 KWBC 132139
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
538 PM EDT THU JUL 13 2017

...VALID 2138Z THU JUL 13 2017 - 12Z FRI JUL 14 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 SW OLS 20 W TUS 30 SSE SOW 20 SSW GNT 50 SSW AEG 25 N TCS
50 WSW DMN 75 SE DUG 95 SSE DUG 105 ENE MMHO.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
RUE 10 NNW VBT 30 ENE WLD 30 W P28 10 ESE CAO 45 ESE LVS
25 WNW 4CR 20 NE AEG 30 SE E33 20 WSW GUC 10 WSW CCU 25 ENE COS
ITR 35 S HDE 25 NNE STJ 30 SSW PPQ MTO 20 W AID 15 SSE TOL
25 N CGF 10 N IAG 10 W FZY 10 NNE DDH 20 NW PVC 65 E CQX
85 ESE ACK 85 S ACK 40 ESE ACY JYO LWB 20 WSW 1A6 BWG 20 SSE PAH
15 E M19 RUE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 SSE HTO 15 S PHL 25 NW MRB 15 NNW BKW 15 WNW JKL 15 ESE FTK
20 E PAH 25 SE UNO 25 ESE JLN 25 S EMP 25 S MHK 30 WNW TOP MCI
35 NNE VIH OLY 15 WNW BAK FDY 10 WSW AKR 15 ESE JHW 20 SSW UCA
OWD 35 ESE CQX 50 SSE ACK 55 SSE HTO.


2100 UTC UPDATE...

MADE GENERALLY SLIGHT ALTERATIONS TO THE DAY 1 ERO BASED ON THE
LATEST MESOANALYSIS/CONVECTIVE TRENDS...RECENT SHORT-TERM QPF
GUIDANCE (ESPECIALLY FROM THE CAMS)...LATEST FFG...AND CURRENT
NATIONAL WATER MODEL SOIL MOISTURE ANALYSIS.
THE UPSHOT IS AN OVERALL SOUTHWARD SHIFT IN BOTH ELONGATED
MARGINAL AND SLIGHT OUTLOOK AREAS...CORRESPONDING TO THE AXES OF
HIGHER PW AND AVAILABLE DEEP-LAYER INSTABILITY.

HURLEY

1500 UTC UPDATE...

WPC MADE SOME MODIFICATIONS FROM THE EARLIER FORECAST AND DECIDED
TO CONNECT THE TWO SLIGHT THREATS INTO ONE, FROM SOUTHERN NEW
ENGLAND TO MID MS VALLEY/CENTRAL PLAINS. THE COMBINATION OF
DECAYING MESOSCALE SYSTEMS AND A SHARP FRONTAL ZONE WILL CONTINUE
TO CLASH WITH ANOMALOUS MOISTURE CONTENT POOLING INVOF AND AHEAD
OF THE BOUNDARY. ONE DECAYING COMPLEX IS ROLLING DOWNSTREAM INTO
WRN NY/PA, WHILE EXTENDING SOUTH AND WEST THROUGH CENTRAL/SRN OH
INTO SRN IN/IL. THIS SYSTEM SHOULD TRANSITION DOWNSTREAM ALONG A
QUASI-STATIONARY FRONT ACROSS CENTRAL NY AND TRIGGER AFTN/EVENING
CONVECTION NEAR COASTAL NORTHEAST/SRN NEW ENGLAND, THOUGH ITS
UNCERTAIN ON THE ORGANIZATION AND THE NORTHERN/SOUTHERN EXTENT.
MEANWHILE INCREASING ACTIVE CONVECTION WITH SLIGHT STEERING MOTION
IS ALLOWING LINE SEGMENTS TO FLOURISH OVER SRN IL/IN AND
CENTRAL/SRN OH. THIS AREA COULD BECOME PROBLEMATIC OVER THE NEXT
SEVERAL HRS, AS WPC WAS TEMPTED TO RAISE THE SLIGHT TO MODERATE
BASED ON LOW FFG BUT HELD OFF AT THE MOMENT. WPC ALSO EXTENDED THE
SLIGHT BACK INTO CENTRAL MO TO NERN KS NEAR THE I70 CORRIDOR, AS
THIS IS AN AREA THE 12Z NAM CONEST LIKES FROM JUST SOUTH OF THE KC
AND STL METRO AREAS. A SEMI-DIFFICULT AND NOT CLEAR-CUT FORECAST
BUT INGREDIENTS ARE IN PLACE FOR LOCALIZED FLOODING FROM HEAVY
RAIN OVER THE NEXT 21 HRS.

MUSHER


...EASTERN OHIO VALLEY / WESTERN MID ATLANTIC...

SOME LARGER SCALE FORCING WILL TAKE PLACE TODAY AS THE STALLED
UPPER LOW OVER NORTHERN MINNESOTA IS KICKED BACK INTO THE WESTERLY
FLOW...CAUSING SOME AMPLIFICATION OF TROUGHING OVER THE GREAT
LAKES / OHIO VALLEY. THIS WILL PUSH A LOCAL MAXIMUM OF DEEP LAYER
MOISTURE / PRECIPITABLE WATER VALUES AROUND 2 INCHES...AND 2.5
STANDARD DEVIATIONS FROM AVERAGE...INTO THE EASTERN OHIO VALLEY.
AT THE SAME TIME...LOWER TO MIDDLE LEVEL CONVERGENCE / CONFLUENCE
WITHIN WEST TO SOUTHWESTERLY FLOW WILL FAVOR ORGANIZED CONVECTIVE
SYSTEMS WITH OUTFLOWS AND REGENERATION POINTS DROPPING ONLY SLOWLY
SOUTH AND EAST. THE FLOW REGIME IS NOT IDEAL FOR TRAINING...WITH
CORFIDI VECTORS FOR FORWARD PROPAGATING SYSTEMS ORIENTED INTO THE
INFLOW RATHER THAN PARALLEL...BUT THE CROSSING ANGLE IS SMALL
ENOUGH THAT THERE SHOULD BE AT LEAST BRIEF PERIODS OF TRAINING.
THE HI-RES MODELS IN PARTICULAR WERE EMPHATIC IN SIGNALING LOCAL
AMOUNTS OF 3-PLUS INCHES...AND THEY CLUSTER VERY WELL
SPATIALLY...HITTING EASTERN OHIO...NORTHERN WEST VIRGINIA...AND
SOUTHWEST PENNSYLVANIA. THIS IS WHERE THE WPC MANUAL FORECAST
INCREASED TO AREAL AVERAGE 2.00 TO 2.50 INCHES. IN ITSELF...THIS
IS NOT EXCEPTIONALLY HEAVY...BUT THERE IS POTENTIAL FOR EXTREME
RAINFALL AMOUNTS ON SMALLER SCALES GIVEN THE 2.5 STANDARD
DEVIATION PW ENVIRONMENT AND MODERATE INSTABILITY. OF EVEN MORE
CONCERN...THE AREA MOST LIKELY TO SEE HEAVY RAINFALL HAS BEEN IN A
WET PERIOD WITH RAINFALL 1 TO 3 INCHES ABOVE AVERAGE THE PAST 7
DAYS...AND A CORRESPONDING DIP IN FLASH FLOOD GUIDANCE VALUES. THE
RISK OF FLASH FLOODING APPEARS FOCUSED TODAY OVER PARTS OF
OH/WV/PA. PER COORDINATION WITH WFO PBZ...CLE...RLX...WE WILL
EXPAND THE COVERAGE OF SLIGHT RISK...AND LOOK CLOSELY AT TRENDS
LATER THIS MORNING FOR POSSIBLE UPGRADE TO MODERATE RISK.


...NORTHERN MID ATLANTIC / NEW YORK / SOUTHERN NEW ENGLAND...

THE SOUTHWARD EXTENSION OF DEEP LAYER TROUGHING OVER
CANADA...ALONG WITH AN EMBEDDED MORE FOCUSED SHORTWAVE
IMPULSE...WILL SUPPORT SCATTERED STRONG CONVECTION INTO THE EARLY
MORNING HOURS OVER CENTRAL/SOUTHERN NEW YORK AND OVER INTO
SOUTHERN NEW ENGLAND. INSTABILITY AND RAIN RATES WERE GREATEST
NEAR AND SOUTH OF A FRONTAL BOUNDARY...BUT WIDESPREAD SHOWERS WILL
ALSO OCCUR FARTHER NORTH WITHIN AN UPGLIDE / WARM ADVECTION
REGIME. THE COMPOSITE LARGER SCALE WAVE MOVES OFFSHORE BY
MIDDAY...BUT ENERGETIC WESTERLY FLOW REMAINS IN PLACE...SUITABLE
FOR ORGANIZED STORM MODES AS NEW CONVECTION FORMS AMID DAYTIME
HEATING...WITH MODERATE INSTABILITY BUILDING UP FROM
CENTRAL/EASTERN PA INTO SOUTHERN NY AND ACROSS COASTAL SOUTHERN
NEW ENGLAND. THE REGION WILL BE IN BETWEEN BETTER DEFINED
SHORTWAVE TROUGHS DURING PEAK HEATING...BUT THE DEGREE OF
INSTABILITY AND MOISTURE SHOULD COMPENSATE TO YIELD SOME ORGANIZED
STORMS WITH VERY HEAVY RAIN RATES. DEEP LAYER LIFTING WILL
INCREASE AGAIN TOWARD MID EVENING NEAR THE I-95 CORRIDOR...AND MAY
BOOST RAINFALL TOTALS SHOULD STORMS BE SLOW TO EXIT THE AREA...OR
SHOULD THE MID LEVELS REMAIN UNSTABLE WITHIN THE BROADER CORRIDOR
OF FAVORABLE DEEP LAYER MOISTURE. GIVEN THESE FACTORS...WPC
INCREASED QPF HERE. ALTHOUGH MODEL QPF SIGNAL WAS NOT VERY
CONSISTENT...WE DID SEE SOME HEAVY TOTALS WEST TO EAST ACROSS THE
NEW YORK CITY AREA FROM SEVERAL MODELS INCLUDING THE
ECMWF...UKMET...AND CANADIAN GEM REGIONAL. HEAVY RAIN IN THE NCEP
HI-RES WINDOWS WAS A LITTLE MORE SPOTTY OR SOMEWHAT VARIABLE IN
LOCATION. WPC QPF FOLLOWED AREAS OF LOW LEVEL CONVERGENCE
DOWNSTREAM OF THE TERRAIN WHERE THE AFTERNOON ACTIVITY IS LIKELY
TO INITIATE.


...LOWER MISSOURI VALLEY AND CENTRAL PLAINS...

PERIODS OF SLOW MOVING...QUASI-ORGANIZED CONVECTION ARE EXPECTED
IN THE NARROW ZONE ALONG AND ESPECIALLY NORTH OF A SURFACE FRONTAL
BOUNDARY...WITH CONVECTION SHY TO ENTER THE DRIER...MORE DEEPLY
MIXED AIR SOUTH OF THE FRONT. EXPECT A LATE DAY AND OVERNIGHT
MAXIMUM OF COVERAGE...AS WAS SEEN LATE WEDNESDAY. THE FRONTAL ZONE
IS FORECAST TO SLIP SOUTHWARD JUST ENOUGH TO PLACE THE RAINFALL
MAXIMUM LIKELY OUTSIDE OF AREAS THAT WERE HIT WITH HEAVY RAIN ON
WEDNESDAY...THUS WE HAVE MAINTAINED ONLY MARGINAL RISK
PROBABILITIES.


...SOUTHWEST U.S...

THE GREATEST AVAILABILITY OF MONSOONAL MOISTURE IS ACROSS SOUTHERN
AZ AND NM. PARTS OF THIS AREA...ESPECIALLY SOUTHEAST
ARIZONA...WILL SEE ENHANCED PROBABILITIES OF LOCAL RAINFALL
EXCEEDING FLASH FLOOD GUIDANCE DURING DIURNALLY DRIVEN
THUNDERSTORMS...AS MODERATE INSTABILITY COINCIDES WITH WEAK
STEERING FLOW.


...UPPER PENINSULA OF MICHIGAN...

ALTHOUGH LOCATED BEHIND THE SYNOPTIC COLD FRONT IN THE OHIO
VALLEY...THE UPPER PENINSULA OF MICHIGAN WILL EXPERIENCE SOME
WRAP-AROUND MOISTURE...ANOMALOUS EASTERLY WINDS TRANSPORTING AIR
CHARACTERIZED BY PW VALUES OF 1.25 INCHES...ESPECIALLY THE EASTERN
PART OF THE PENINSULA. WITH AN UPPER LOW SLIDING INTO AND
UNDERNEATH THIS PLUME OF MOISTURE...CONVECTIVE RAIN AND
THUNDERSTORMS MAY BE VERY SLOW MOVING. THE HI-RES MODELS INDICATE
SOME POCKETS OF 1 TO 2 INCH RAINFALL...AND ISOLATED HIGHER AMOUNTS
ARE POSSIBLE GIVEN THE PERSISTENCE OF THE EASTERLY FLOW.

BURKE
$$





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