Quantitative Precipitation Forecast
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FOUS30 KWBC 170035
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
834 PM EDT SUN JUL 16 2017

...VALID 01Z MON JUL 17 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
130 SSW GBN 70 SE YUM 20 ESE YUM 30 WNW IFP 50 NE IGM
45 NNW INW 45 WSW RQE 10 W GUP 35 SSE DRO 35 SSE GUC 20 WNW AFF
20 NNW LIC 35 W IML 35 SSW LBF 40 WSW HLC 20 SE GCK 10 SE GAG
35 WNW CSM 20 NNE DUX 40 NE TCC 50 E CQC 20 SE 4MY 65 SSW ABQ
40 N SVC 50 SSW DMN 110 SW MMCS 115 NW MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 E SGJ 35 WNW JAX DQH 20 ENE BGE 20 SSE PAM 55 SW PAM
25 SSE KVOA 15 WSW KMDJ 20 S SRN 35 SE KXIH 30 SE KXIH
25 NW KBBF 2R8 PKV 5R5 10 E BPT 35 E CWF HDC 20 W HBG 10 SSW MEI
15 WNW AUO 10 NE ANB 25 S 4A9 10 SSE DNN 20 SW 1A5 15 ESE 1A5
10 S EQY 25 E EQY 10 SSW LHZ 15 SSW FKN 55 ENE FFA 100 ENE HSE
100 ESE HSE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 ESE HXD 10 NE SAV 10 SW TBR 30 N VDI 25 S HQU 30 WSW CAE
10 E MMT CTZ GSB 10 WSW EDE 20 SE MQI 50 SE HSE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 WSW OLS 90 S GBN 45 WSW GBN 20 WNW PRC 25 SE FLG 20 NNE SOW
50 SE SOW 40 SE SAD 55 SSE DUG 95 NE MMHO.


17/01Z UPDATE...

...ACRS THE SW...
MAIN CHANGE WAS TO TRIM MARGINAL RISK AREA WHERE STGR CONVECTIVE
THREAT CONTINUES TO DIMINISH WITH LOSS OF AFTN HEATING.  ACROSS
AZ...MAINTAINED MUCH OF THE EARLIER SLIGHT RISK AREA WITH SEVERAL
STORM CLUSTERS MOVING SWWD OFF THE MOGOLLON RIM TOWARD UNTAPPED
HIER CAPE/MSTR PROFILES.  VIS IMAGERY ALSO SHOWS AREA OF ENHANCED
CU AND EMBDD STORMS WORKING WWD ACRS SE AZ AND WRN NM..WHICH COULD
YIELD SOME MERGERS WITH ACTIVITY FARTHER TO THE NORTH THIS
EVENING/OVERNIGHT.  SLOWER MOVING CELLS ESPECIALLY DURING EARLY
STAGE OF DVLPMENT COULD BE ACCOMPANIED BY SOME SHORT TERM BUT
INTENSE RAIN RATES GIVEN THE RATHER HI PWS.

...ACRS ERN CO/WCNTL PLAINS...MODELS SHOW SOME INCREASE IN THE LOW
LEVEL S/SELY FLOW TO THE EAST OF PESKY MID LEVEL LOW/SHEAR AXIS
OVER ERN CO THAT MAY ALLOW STORMS TO BECOME A BIT MORE FOCUSED
WITH SOME TRAINING POTNL OVERNIGHT ACRS EXTREME ERN CO INTO
ADJACENT AREAS OF KS/OK/NEB.  THE NAM CONEST IS THE MOST ROBUST
WITH PCPN AND MAY BE OVERDONE...BUT THE HRRR AND HRRR EXPERIMENTAL
INDICATE THE POTNL FOR ISOLD AMOUNTS IN EXCESS OF 1.5".  GIVEN THE
UNCERTAINTY HERE...HAVE MAINTAINED A MARGINAL RISK ACRS THIS
REGION.

..ACRS THE CAROLINAS SWWD ALONG THE GULF COAST...

THE MORE FOCUSED CONCERN WOULD APPEAR TO BE ACRS THE COASTAL
CAROLINAS INTO ERN GA THIS EVENING WITH MERGING OUTFLOW/SEA
BREEZES LEADING TO SOME SHORT TERM BUT VERY INTENSE CONVECTIVE
RAINS.  ALREADY HAVE SEEN REPORTS OF OVER 3 INCHES IN AN HOUR OR
LESS AND WITH PWS IN EXCESS OF 2 INCHES ACROSS THIS AREA...SO
EXPECT THREAT OF ADDITIONAL HEAVY RAINS TO LINGER OVERNIGHT..BUT
ESPECIALLY THROUGH THE EARLY EVENING HOURS WITH VERY GRADUAL
SHARPENING OF TROF AXIS THROUGH THE TN VALLEY.  HAVE MAINTAINED
MARGINAL RISK ALONG MUCH OF THE GULF COAST WWD INTO THE MID/UPR TX
COAST..GIVEN SIGNAL IN THE HRRR RUNS OF STORMS POSSIBLY DVLP ALONG
DEEPER PW AXIS HOVERING NEAR THE COAST OVERNIGHT AND TOWARD
MORNING.   SULLIVAN   PREVIOUS DISCUSSIONS FOLLOW...



...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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