Quantitative Precipitation Forecast
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FOUS30 KWBC 241456
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1054 AM EDT MON JUL 24 2017

...VALID 15Z MON JUL 24 2017 - 12Z TUE JUL 25 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW CXSH CMGB 10 SW 1V4 VSF 10 ESE ORE BOS OQU FOK 30 SSE ACY
10 N GED 10 ESE THV 20 SW IPT ELM 15 WSW ROC 20 ESE CWNC
30 WNW CWRK 25 SE CWBA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 WNW MMHO 80 SSE YUM 25 W NYL 25 ESE IPL 30 ESE TRM 25 SE TRM
40 SE CZZ CZZ 10 SSE RIV POC 30 ESE EDW 25 ESE NID 55 W DRA
45 SSW TPH 35 NNW TPH 20 E NFL 30 NW LOL 70 SE AAT 40 E AAT
55 SW REO 50 NNW AWH 50 N 9BB 20 NNW ENV 35 NNE DPG HIF
25 SE FIR 40 WNW VEL 55 S VEL RIL 20V 30 WSW AFF 20 ENE VTP
30 ESE LVS 35 NNW ROW 40 NW GDP 40 SE MMCS 75 N MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW NMM 15 NE DHN 25 SE VLD 20 NW OCF 60 W BKV 65 SW AAF
15 N KVOA 15 W KMIS 2GL 25 ENE BPT 20 E UTS 15 S BMQ 35 NE E29
45 S DYS 15 NNE 7F9 15 N TRL 20 ENE 4F4 35 WNW MLU 30 SSE LLQ
40 SE SGT 35 NNW GWO 20 NNW NMM.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 S OLS 55 WSW TUS 65 S GBN 50 SW GBN 35 WNW GBN 25 SE BLH
10 NNE EED 35 WNW IFP 65 SSW HND 55 NE DAG DRA 50 N DRA
40 NNE TPH 55 W P68 15 NE P68 50 SSW ENV 25 NNW MLF 50 WNW 4HV
30 NW PGA 40 ENE GCN 65 SSE PGA 60 ESE PGA 40 SSW 4BL 35 N 4BL
15 WSW MTJ 35 S GUC 25 WSW ALS 35 WSW SKX 25 W SAF 45 N 4SL
40 WNW 4SL 10 W GNT LRU 55 SSW MMCS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W IER 20 E ESF 25 NE HEZ 35 SSE JAN 30 E HBG 10 WNW HRT PFN
30 WSW PAM 40 SSE JKA 30 N KMIS 25 W MSY 30 NE BPT 25 SW LFK
15 E TPL 10 NW CNW 20 E LNC 20 SSW 4F4 20 W IER.



...15Z UPDATE...

WPC WENT AHEAD AND ADDED NJ, PARTS OF EASTERN PA AND DE/NERN MD
INTO THE MARGINAL THREAT THAT ALREADY INCLUDED MUCH OF NY STATE
AND PARTS OF NEW ENGLAND FOR ALREADY ONGOING ACTIVITY NEAR UPSTATE
NY BUT ALSO THE ANTICIPATION OF CONVECTION THIS AFTERNOON AHEAD OF
THE ARRIVING COLD FRONT WHICH COULD PRODUCE LOCALLY HEAVY RAIN
AMOUNTS BUT ADD TO THE TOTALS FROM EASTERN/SERN PA SOUTHWARD FROM
YESTERDAY.

MEANWHILE, WPC EXPANDED THE SLIGHT RISK FOR EXCESSIVE FROM EASTERN
TX THROUGH CENTRAL LA INTO SOUTHERN MS/AL INTO THE WESTERN FL
PANHANDLE AS HI-RES GUIDANCE HAS A GOOD HANDLE AND SIGNAL FOR
EXCESSIVE RAIN AMOUNTS ALONG THIS AXIS NEAR A SHEAR
AXIS/PRE-FRONTAL TROUGH WITH VERY LIGHT STEERING MOTION.

FINALLY IN THE SOUTHWEST, PRETTY MUCH KEPT CONTINUITY FROM
OVERNIGHT. WPC DID SLIDE THE MARGINAL THREAT TO THE SOUTHERN CA
TERRAIN/MTNS AND BASED ON THE INTENSIFICATION NEAR THE MID-LEVEL
VORTICITY NEAR THE PHX METRO AREA THIS MORNING, CONSIDERED A SMALL
MODERATE THREAT FOR THE SHORT TERM BUT HELD OFF AND ALLOWED MPD
551 TO COVER THE THREAT.

MUSHER


...DESERT SOUTHWEST/GT BASIN...

THE MUCH ABOVE AVERAGE MONSOONAL PW VALUES WILL PERSIST ACROSS THE
SOUTHWEST U.S. DAY 1 WITH MODELS SHOWING STG NWD SURGE OF 1.75 TO
2" PWS ACRS S/SW AZ WITH 1.5+ PWS EXTENDING NWD INTO SRN NV/SW UT
BY MON NIGHT.  MODELS INDICATE SEVERAL WEAK VORT MAXIMA LIFTING
NWD BETWEEN WEAK UPPER RIDGE OVER THE ROCKIES AND UPPER TROF/LOW
ALONG THE NRN CA COAST.  THE MORE SIGNIFICANT ONE IS GENLY
FORECAST TO LIFT TOWARD NW AZ BY MON EVENING.  INCREASING UPPER
SHEAR/DIFFLUENCE ALOFT COMBINED WITH STG NWD MSTR FLUX AND VORT
MAXIMA SHOULD SIGNIFICANTLY INCREASE HEAVIER RAIN THREAT AND
POSSIBLE FLASH FLOODING CONCERNS ACRS AZ INTO PARTS OF NV/UT THIS
PD INCLUDING PARTS OF SW CO...WITH MORE WIDESPREAD SCTD
SHOWERS/TSTMS SPREADING WWD INTO SRN CA AND NWD THROUGH THE GT
BASIN INTO PARTS OF OREGON/ID. FORECAST SOUNDING SHOWS FAVORABLE
MSTR/INSTABILITY PROFILES DVLPG BY LATER MON/MON EVENING TO
SUPPORT HEAVIER RAIN THREAT INTO THE NORMALLY DRIER DESERT
AREAS..INCLUDING THE LAS VEGAS AREA. FOR THIS REGION HAVE
EXTENDING BOTH MARGINAL AND SLIGHT RISK AREAS WWD ACS THE CNTL GT
BASIN..WITH ISOLD FF RISK EXTENDING INTO PARTS OF SRN CA.

 ...SE U.S. INTO THE GULF COAST STATES/FL...

THE FRONTAL BOUNDARY INITIALLY OVER THE TN VALLEY WWD INTO THE SRN
PLAINS IS EXPECTED TO CONTINUE PUSHING SLOWLY SWD THIS PD IN
RESPONSE TO WEAK HI PRESSURE BUILDING IN BEHIND UPPER TROF PUSHING
ACRS THE GT LAKES/NE.   WIDESPREAD SCATTERED CONVECTION WILL
LIKELY CONTINUE IN THE VICINITY OF THIS FRONT AS VERY HIGH
PWS..AOA 2"..REMAIN POOLED ALONG AND JUST AHEAD OF THE BNDRY.
MODELS INDICATE INCREASING WLY 85H FLOW FROM ERN TX THROUGH THE
CNTL AND ERN GULF COAST OF BETWEEN 20 TO 25 KTS UNDER REGION OF
WEAK ANTICYCLONIC SHEAR.  THIS COULD LEAD TO A RELATIVE MAXIMA OF
PCPN FROM PARTS OF THE CNTL GULF COAST IN THE FL PANHANDLE REGION
DAY 1 WHICH IS SUPPORTED BY SEVERAL 00Z HI RES MODEL RUNS.  AREAL
AVG AMOUNTS OF OVER AN INCH ARE LIKELY WITH LOCAL STORM TOTAL
AMOUNTS IN EXCESS OF 3 INCHES PER CONSENSUS OF HI RES GUIDANCE.
THIS COULD LEAD TO LOCALIZED FLASH FLOOD CONCERNS.  A SLIGHT RISK
WAS INTRODUCED ACRS PARTS OF THE CNTL GULF COAST WHERE RECENT
HEAVIER RAINS HAVE LEAD TO LOWER FFG VALUES/WETTER SOIL
CONDITIONS..LEADING TO POTNL FOR EXPECTED RAINS TO EXCEED THOSE
FFG VALUES.

...NORTHEAST U.S...

UPPER TROF IS FCST TO CONTINUE A GRADUAL EWD PROGRESSION ACRS THE
GT LAKES WHILE SLOWLY WEAKENING OVER NEW ENGLAND BY TUES MORNING.
THE MORE CONCENTRATED RAINS WILL OCCUR AHEAD OF THE MAIN UPPER
TROF AND ASSOC SFC LOW MOVING ACRS NY STATE INTO WRN PORTIONS OF
NEW ENGLAND..WHILE ANOTHER FAIRLY INTENSE AREA OF CONVECTIVE RAINS
WILL BE ONGOING AT THE BEGINNING OF THE PD ASSOCD WITH A LOW PRES
SYSTEM RIDING NEWD OFF THE MID ATLC COAST.  THE LATTER WILL
PRIMARILY AFFECT PORTIONS OF CT EWD INTO ERN/SERN MA..WITH STG BUT
NARROW FORCING AHEAD OF THE WAVE AND ASSOCD WARM FRONT.   THE NAM
SEEMS TO BE AN OUTLIER SOLN WITH THE MORE NRN TRACK OF THE LOW AND
ASSOCD PCPN AS IT IS A BID MORE AMPLIFIED WITH THE UPPER TROF.
HAVE GONE WITH A NON-NAM CONSENSUS HERE WHICH ONLY BRINGS LIGHTER
RAIN AMOUNTS INTO DOWNEAST PORTIONS OF MAINE.  SLOW MOVEMENT OF
THE UPPER TROF AND ASSOCD LOW MOVING ACRS NY STATE IS EXPECTED TO
PRODUCE .50 TO 1+ INCH AREAL AVG AMOUNTS FROM CNTL NY NWD
INCLUDING PORTIONS OF NRN VT.  MODELS SHOW POTNL FOR NARROW AXIS
OF 500 TO 1000 J/KG CAPES DVLPG DURING THE AFTN ACRS WRN NY WHICH
COULD SUPPORT SOME ISOLD HEAVIER RAIN RATES.  PWS ARE ONLY
MARGINALLY HIGH..BUT SLOW MOVEMENT OF CELLS TO THE EAST COULD LEAD
TO SOME ISOLD RAINS IN EXCESS OF AN INCH AN HOUR..WHICH COULD LEAD
TO SOME ISOLD RUNOFF ISSUES.


SULLIVAN
$$





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