EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
858 PM EDT MON JUL 24 2017

...VALID 01Z TUE JUL 25 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
45 E NRB 20 N GNV 20 SE TLH 15 E PAM VPS JKA GPT 20 ENE NBG GAO
15 SE 7R3 PTN 10 NE ARA 45 SSE ESF 35 WNW HEZ 35 SW GLH
45 SE UTA 20 SSE 1M4 20 W LGC VDI 20 NNE NBC 15 ESE MYR
80 SSE MYR.

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
30 NNW NJK 40 SE CZZ 20 S CZZ 20 SE RIV 20 N EMT 30 NW DAG
60 W DRA 20 ENE MMH 10 ESE TRK 30 E LMT 50 SE RDM 35 ENE 5J0 MUO
15 E JER 15 S 77M DPG 20 SSW PVU 45 ENE PVU 35 E VEL 20 WNW CCU
10 N VTP 25 NE LVS 15 E CQC 20 SW 4MY 25 NE ALM 50 SSE MMCS
75 N MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E WWD 30 SSE WWD 10 SSW GED 10 NW CGE NAK CGS GAI 20 NNE GAI
20 N DMH 10 NNE APG 15 N ILG UKT 10 SSW MPO 15 N AVP 25 SSE BGM
35 NE BGM 25 SSE UCA 40 W SCH 45 SW SCH 15 NE MSV 15 NE FWN
15 W HPN 15 SSW JFK 20 ESE BLM 25 SSE MJX.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 S OLS 60 WSW TUS 35 S GBN 30 NW GBN 50 NE YUM 25 ESE BLH
50 ESE EED 15 WNW IFP 50 NNE NXP 45 S DRA 50 N DRA 50 NW TPH
30 SW NFL 35 NE RNO 20 NW LOL 50 S B23 15 NE P68 50 SSW ENV
45 NNW MLF 55 NW 4HV 40 NNE U28 20 WSW GUC 15 E SKX 15 WSW LVS
10 S SAF 20 NNE 4SL 35 W 4SL 20 SSE GNT LRU 80 SSW MMCS.


2100-0100 UTC UPDATES...

UPDATED THE DAY 1 ERO TO REALIGN THE SLIGHT AND MARGINAL OUTLOOKS
BASED ON THE LATEST OBSERVATIONAL/MESOANALYSIS/CONVECTIVE
TRENDS... WHILE INCORPORATING THE MORE RECENT HIGH-RES GUIDANCE
(INCLUDING HRRR) ALONG WITH THE LATEST SSEO 40KM NEIGHBORHOOD
PROBABILITIES OF 3 HOURLY QPF EXCEEDING 3 HOURLY FFG. OUTSIDE OF
THE ONGOING MONSOONAL CONVECTION OUT WEST...THIS INCLUDED PARING
THE MARGINAL AREAS ACROSS THE UPPER MID ATLANTIC-NORTHEAST AND
ACROSS THE LOWER MS VALLEY INTO THE SOUTHEAST.

HURLEY


1500 UTC 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