Quantitative Precipitation Forecast
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FOUS30 KWBC 161453
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1053 AM EDT SUN JUL 16 2017

...VALID 15Z SUN JUL 16 2017 - 12Z MON JUL 17 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 ENE SGJ 25 SE SGJ 25 NE VVG 25 ESE CTY 25 S AAF 35 SSW JKA
GSM 30 E KXIH 25 SE KBQX KOPM 20 ESE BKS 25 NNW VCT 15 NNW UTS
40 NNE IER 20 ESE TVR CBM 20 SW CSV 25 SW TYS 25 NNE AVL JQF
10 ESE TDF 20 NNE LFI 110 ESE WAL 175 E FFA 205 ESE HSE
200 SE HSE 185 SE MRH.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
130 SSW GBN 40 SE YUM 35 NNE YUM 30 NE IGM 30 NNW GCN 60 N INW
55 NNW RQE 30 W TEX 20 ENE MTJ 15 N MYP 40 W FCS 10 E APA
35 SSW IBM 20 NE OGA 35 SE MCK 30 NE GCK 20 ESE HHF 40 SW SPS
30 NNE DYS 35 ENE LBB 15 S AMA 15 S GUY 20 NNW CAO 50 NW TCC
20 ENE CQC 10 NW AEG 55 NNW TCS 15 ENE DMN 95 SW MMCS
145 ENE MMHO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 E SSI 35 S AYS 35 NNE BFM 55 ESE NMM 15 ESE OPN 10 ENE DNL
20 ENE DNL 10 SSE MEB 20 N PGV ECG 30 ENE FFA 105 E HSE
100 SE HSE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 WSW OLS 50 WSW GBN 60 WNW LUF 35 WNW PRC 25 SSW 40G
25 ESE FLG 25 SE INW 15 NW SJN 10 NNW SJN 35 ESE SJN 35 NW SVC
70 E DUG 80 SSE DUG 95 S DUG.


...15Z UPDATE...

WPC MADE VERY MINOR TWEAKS FROM THE PREVIOUS ISSUANCE, TO KEEP
CONTINUITY. INCLUDED A MARGINAL THREAT DOWN THE COAST OF TX, ALL
OF THE FL PANHANDLE AND INTO THE EASTERN TX PANHANDLE AREA. FOR
THE FORMER, JUST IN CASE OFFSHORE CONVECTION MOVES ONSHORE AS A
FEW HI-RES MODELS INDICATE POSSIBLE. FOR THE MIDDLE, WIDESPREAD
ONSHORE CONVECTION LINES SPREADING INTO THE PANHANDLE WITH MORE
OFFSHORE ACTIVITY POSSIBLY REACHING THE REGION LATER. FOR THE
LATTER, SOME SIGNAL FROM THE HI-RES GUIDANCE ON A NARROW AXIS OF
HEAVY CONVECTIVE RAINS EXPECTED LATER TODAY AND CAPTURE THE
PERSISTENT MAINLY LIGHT CONVECTIVE SHOWERS NEAR CDS THIS MORNING.
THE ONLY ADJUSTMENT TO ANY SLIGHT THREAT WAS TO EXTEND THE AREA
WEST FROM SOUTH CENTRAL GA INTO AL. POSSIBLE CONVERGENCE ZONE
COULD SET UP HERE, AS ONSHORE/SEA BREEZE ACTIVITY OVER THE FL
PANHANDLE INTERACTS WITH OUTFLOW PESKY ACTIVITY MAINLY SOUTH OF
BHM/ATL.

MUSHER


...GEORGIA AND THE EASTERN CAROLINAS...

SOUTHEAST GEORGIA AND THE COASTAL CAROLINAS SIT IN A FAVORABLE
POSITION FOR ENHANCED COVERAGE OF AFTERNOON CONVECTION PRODUCING
HEAVY RAIN. EASTERN U.S. TROUGHING WILL UNDERGO SLIGHT
AMPLIFICATION TODAY WITH THE MEAN TROUGH AXIS BACK ACROSS WESTERN
GEORGIA AND ALABAMA. THIS PLACES THE SOUTHERN ATLANTIC COAST
BENEATH SLIGHTLY DIFLUENT UPPER FLOW WHICH WILL AIDE THUNDERSTORM
GROWTH...INTENSITY...AND LONGEVITY...AS STORMS INITIATE NEAR THE
COASTAL CONVERGENCE ZONE / SEA BREEZE AND ALSO WITHIN THE MOIST
AND STRONGLY HEATED ENVIRONMENT FARTHER INLAND TOWARD A SLOWLY
SAGGING FRONTAL BOUNDARY. IN THE ABSENCE OF A WELL DEFINED UPPER
SHORTWAVE...AND WITH MODEST DEEP LAYER WIND SPEEDS AND SHEAR...IT
WILL BE DIFFICULT TO ANTICIPATE EXACTLY WHERE CONVECTION WILL
BECOME MORE ORGANIZED...BUT THE MODEL QPF SOLUTIONS ARE
INCREASINGLY CONFIDENT IN AN AXIS OF ORGANIZED HEAVY RAINFALL FROM
SOUTH OF MACON OVER TOWARD SAVANNAH AND CHARLESTON...AND
CONTINUING UP THE COAST INTO THE OUTER BANKS. WITH PRECIPITABLE
WATER AROUND 2 INCHES...THERE WILL BE VERY HEAVY RAIN RATES IN THE
STRONGEST CELLS...WITH POTENTIAL FOR ISOLATED 4-PLUS INCH AMOUNTS
WHEREVER CELL MERGERS OR TRAINING OCCURS.


...ARIZONA AND WESTERN NEW MEXICO...

THE PAST FEW DAYS HAVE BEEN ACTIVE FROM THE MOGOLLON RIM
SOUTHWARD...AND AS MOISTURE DEPTH CONTINUES TO CREEP WEST THROUGH
THE DESERTS WE SAW AN ENVIRONMENT ON SATURDAY THAT SUPPORTED
CONVECTION SURVIVING DOWN INTO THE VALLEYS AND DESERT AREAS OF
SOUTHERN ARIZONA. SUNDAY SHOULD BE SIMILAR AS STEERING FLOW
REMAINS NORTHEAST TO SOUTHWEST...WITH THE RIDGE POSITION OVER THE
NV/UT BORDER. CONSENSUS QPF AND THE WPC MANUAL FORECAST HIGHLIGHT
CENTRAL ARIZONA WITH SOME ROBUST AREAL AVERAGE PRECIPITATION. THE
SETUP IS NOT OVERLY FAVORABLE FOR CELL TRAINING...BUT THERE IS
USUALLY SOME SLOW MOVEMENT IN THE EARLY STAGES BEFORE A LARGER
COLD POOL IS BUILT. ONE OF THE CONCERNS TODAY...IS THAT ALL OF THE
HEAVY RAIN PARAMETERS CONTINUE TO INCREASE JUST AHEAD OF AN
EASTERLY WAVE COMING THROUGH MEXICO. PRECIPITABLE WATER VALUES
SPIKE AT 2.0 TO 2.5 STANDARD DEVIATIONS ABOVE AVERAGE OVER CENTRAL
TO SOUTHERN ARIZONA...AND THE HI-RES MODELS PREDICT AFTERNOON
DEWPOINTS HOLDING UP IN THE 60S...WITH LARGE CAPE VALUES.
THUS...EVEN WITHOUT MUCH TRAINING THE SHORT TERM HEAVY RAIN RATES
MAY BE ON THE EXCEPTIONAL SIDE ON LOCAL SCALES...CAUSING AN
INCREASE TO THE NUMBER OF INSTANCES OF FLASH FLOODING COMPARED TO
RECENT DAYS. AFTER COORDINATING WITH LOCAL FORECAST OFFICES WE
UPGRADED THIS REGION TO A SLIGHT RISK OF EXCESSIVE RAINFALL.
THANKS WFO FGZ...PSR...TWC...EPZ...ABQ.


...NORTHERN NEW MEXICO THROUGH WESTERN KANSAS...

THE SMALL VORTICITY MAXIMUM OVER COLORADO...EMBEDDED IN MEAN
RIDGING...HAD BECOME MORE PRODUCTIVE WITH LARGER SCALE CONVECTION
ON SATURDAY. STILL...ITS RADIUS OF INFLUENCE IS FAIRLY
SMALL...WITH WEAK WIND FIELDS SURROUNDING IT. THE FEATURE WILL
OPEN UP A BIT AND BECOME STRETCHED NORTH TO SOUTH WHILE ALSO
BEGINNING TO LIFT NORTHWARD LATE SUNDAY...UNDER THE ENCOURAGEMENT
OF NORTHERN STREAM FLOW PICKING UP ACROSS THE ROCKIES. THIS SETS
UP AN AXIS OF MODERATE AND LOCALLY HEAVY RAINFALL ALONG THE KS/CO
BORDER AND EXTENDING BACK ALONG THE TRAILING TROUGH AXIS INTO
NORTHERN NEW MEXICO. VERY WEAK STEERING FLOW WILL LEAD TO SLOW
MOVING CELLS...INCREASING THE LIKELIHOOD OF LOCALLY EXCESSIVE
RAINFALL. THIS COULD PROVE PROBLEMATIC IN THE MOUNTAINOUS
TERRAIN...AND ALSO OUT ACROSS THE HIGH PLAINS WHERE SOMEWHAT
STRONGER LOW LEVEL INFLOW COULD SUSTAIN LOCAL POCKETS OF
CONVECTION.


...WESTERN GULF COAST...

BACK WEST...WPC WAS FAIRLY GENEROUS WITH THE AREAL COVERAGE OF
HYDROLOGICALLY SIGNIFICANT PRECIPITATION AT LEAST A QUARTER INCH
OR MORE WITHIN A ZONE OF FAVORABLE MID LEVEL MOISTURE...WHICH WILL
ENHANCE RAINFALL EFFICIENCY FROM SOUTHERN ALABAMA TOWARD THE UPPER
TEXAS COAST. ANYWHERE IN THIS ZONE PW WILL AVERAGE 2
INCHES...LEADING TO THE POTENTIAL FOR RAPID MULTI-INCH RAINFALL
ACCUMULATIONS AND LOCAL FLASH FLOODING. WE WILL ALSO HAVE TO WATCH
THE TX GULF COAST CAREFULLY. HI-RES MODELS ARE INDICATIVE OF VERY
HEAVY RAIN ASSOCIATED WITH A MID LEVEL CIRCULATION NEAR COASTAL
TEXAS...ALTHOUGH THE HEAVIEST MAY TEND TO OCCUR JUST OFFSHORE.

BURKE
$$





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