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Excessive Rainfall Discussion
 
(Latest Discussion - Issued 1350Z Jul 26, 2017)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
950 AM EDT WED JUL 26 2017

...VALID 15Z WED JUL 26 2017 - 12Z THU JUL 27 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W SKX 20 NNW TEX 35 NNE MTJ 10 WNW EGE 40 ENE HDN 30 WSW LAR
10 S PUM 15 S FNL 10 WSW LIC 10 NE LAA 10 ESE LBL 45 NNW GAG
25 SSE GAG 60 W CVS CQC 20 W SKX.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNE GBD 20 S HSI 30 ESE ANW 15 NNE MWM 15 ENE RGK 15 NNE RRL
35 NNW ISQ 25 N ANJ 30 N CWBE 15 NE CYVV 10 SE P58 GRR
15 NNW EKM 10 W FWA 10 WSW AID 20 S HUF BLV 40 SSW SZL 10 NW P28
10 NNE GBD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 ENE SGJ 15 S NIP 20 WNW CTY 30 N AAF 10 NW BGE 40 WSW EZM
20 SW HQU 10 S CUB 35 NE CHS 100 SSE MYR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NNW EHA 30 S SPD 40 E RTN 15 WSW TAD 20 NNW VTP 40 E MYP
30 SW BJC 40 NE PUB 10 SW LAA 35 NNW EHA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NW SUX 15 SSE SPW 20 ESE SPW 20 E MCW LNR 10 SSW SBM
20 ESE SBM MWC JVL 15 SSW RPJ 15 NW IKK 30 NNW LAF 10 SSE LAF
30 SE DNV 10 SE MTO 25 WNW SET COU LXT 25 WSW IXD 25 SE SLN
20 NNE BIE 10 NE OFK 10 NW SUX.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSW AFK 20 NNW AFK 20 WNW CSQ 20 SE OXV FFL 10 NE BRL
10 NW MQB 10 WSW MQB 25 WSW EOK 20 WNW IRK 30 ESE STJ 30 NNW TOP
10 SSW AFK.


1500 UTC UPDATE

NO CHANGES MADE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL
OUTLOOK

ORAVEC

INITIAL DISCUSSION


...CNTL ROCKIES EASTWARD INTO THE MID MS VALLEY/MIDWEST AND GT
LAKES REGION...

   ...SLIGHT TO MDT RISK OF EXCESSIVE RAINS FOR PARTS OF THE MID
MS VALLEY/MIDWEST...
   ...SLIGHT RISK OF EXCESSIVE RAINS FOR PORTIONS OF CNTL TO SE CO
INTO NE NM/EXTREME WRN OK PANHANDLE...

A POTENTIALLY SIGNIFICANT HEAVY RAIN THREAT IS EXPECTED TO UNFOLD
ACROSS PORTIONS OF THE MIDWEST/MID MS VALLEY THIS PD AS
UNSEASONABLY HIGH PWS POOL AHEAD OF A LOW PRES SYSTEM AND ASSOCD
S/WV TROF MOVING EWD FROM THE CNTL PLAINS REGION.  WIDESPREAD
CONVECTION SHOULD BE ONGOING AT THE START OF THE PD AS COMPLEX OF
STORMS MOVE EWD FROM NEB/SD INTO IA ALONG NOSE OF 40 KTS SWLY
JET..WHILE ADDITIONAL SHOWERS SPREAD EWD ALONG ASSOCD COLD FRONT
MOVING ACRS THE GT LAKES REGION MORE TIED TO STGR MID/UPR TROF
MOVING THROUGH SRN CANADA.  BY LATE AFTERNOON AN AXIS OF GREATER
THAN 2.25 INCH PWS...2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL..
WILL BECOME ALIGNED WITH THE CONFLUENT SW TO WLY 85H FLOW AHEAD OF
THE ASSOCD COLD FRONT AND ASSOCD LOW FROM SRN IA SWWD INTO NE KS
WHERE EXPECT STORMS TO RAPIDLY INCREASE AGAIN IN RESPONSE TO
INCREASING MLCAPES AND STG MSTR FLUX.  RAINFALL RATES SHOULD
BECOME QUITE HEAVY AT TIMES DURING THE LATE AFTN AND CONTINUE TO
SPREAD ACRS SRN IA/NRN MO INTO CNTL IL/IN BY THUR MRNG WITH A PD
OF INTENSE SLOW MOVING CELLS WITH POTNL TRAINING EXPECTED AS
STORMS TRACK GENLY EWD WITH A SLOW SEWD OVERALL COMPONENT WED
NIGHT.  THE TREND OF MUCH OF THE 00Z GUIDANCE HAS SUGGESTED A
SOUTHWARD SHIFT TO THE AXIS OF HEAVIER RAINS.  MODEST POSITIONAL
SPREAD REMAINS WITH THE 00Z HI RES GUIDANCE WITH THE DIFFERENCES
TIED TO THE INTENSITY OF THE EARLY MORNING CONVECTION AND WHERE
THE BETTER AFTN CONVERGENCE WILL TEND TO SET UP BEHIND THE INITIAL
CONVECTION.  AT THIS TIME..THOUGHT THE NSSL WRF WAS A GOOD
COMPROMISE SOLN WHICH HELPED MAINTAIN SOME LEVEL OF CONTINUITY
THOUGH SUPPORTED THE GENL SOUTHWARD TREND OF THE MODELS.  IN
ADDITION THE UNSEASONABLY HI PWS AOA 2.25"...THIS WOULD GENLY
SUPPORT SATURATION SOUTHWARD TOWARD HIER THICKNESSES.  WITH
TROPICAL LIKE MSTR...SOME OF THE STRONGER STORMS WILL BE CAPABLE
OF PRODUCING HOURLY RAIN RATES OVER 3 INCHES WITH SOME STORM TOTAL
AMOUNTS OF OVER 5 INCHES EXPECTED. AS A RESULT...FLASH FLOODING
WILL LIKELY BE A CONCERN ACROSS MUCH OF THE MID MS VALLEY MIDWEST
REGION..BUT ESPECIALLY FROM SE NEB/NE KS EASTWARD THROUGH SRN
IA/NRN MO WHERE HAVE UPGRADED AREA TO A MDT RISK OF EXCESSIVE
RAINS.   FARTHER TO THE WEST...OF EQUAL HEAVY RAIN CONCERN WILL BE
ACROSS THE UPSLOPE AREAS OF CO SEWD INTO THE ADJACENT HI
PLAINS..WHERE VERY MOIST AND UNSTABLE POST FRONTAL UPSLOPE FLOW
WITHIN A REGION OF WEAK FLOW NEAR THE CREST OF AN UPPER RIDGE
AXIS..COULD LEAD TO SOME VERY HEAVY SLOW MOVING STORMS LATER
WED/WED NIGHT. HI RES GUIDANCE IS IN RATHER GOOD AGREEMENT HERE
SHOWING POTNL FOR 1 TO 2" AREAL AVG RAINS BOTH TIED TO THE TERRAIN
AND BUILDING/DVLPG SEWD ALONG AXIS OF MODEST CAPES EXPECTED NORTH
OF THE SFC BNDRY. FOR THIS REASON..A SLIGHT RISK OF EXCESSIVE
RAINS HAS BEEN POSTED ACROSS THAT AREA.

...SOUTHEAST...

A WEAK CIRCULATION ALONG THE SC/GA COAST EMBDD WITHIN WEAK
STEERING FLOW IS FORECAST TO MEANDER ACRS THE SE COAST AREA OVER
THE DAY 1 PD.  WITH AIRMASS HERE EXPECTED TO REMAIN VERY
MOIST..WITH PWS AOA 2"..THE POTENTIAL WILL EXIST FOR SOME VERY
SLOW MOVING STORMS TODAY ACCOMPANIED BY LOCALLY HEAVY DOWNPOURS
AIDED BY SEA BREEZE CONVERGENCE.  AREAL AVG RAINS OF 1 TO 2 INCHES
WILL BE PSBL GIVEN THE SLOW MOVEMENT OF STORMS WITH ISOLD HEAVIER
AMOUNTS PSBL.  ISOLD/LOCALIZED FLASH FLOODING WILL CERTAINLY BE
PSBL IN SOME OF THE SLOWER MORE PERSISTENT CELLS  AND HAVE
INTRODUCED A MARGINAL RISK OF EXCESSIVE RAINS FOR THIS REASON.

SULLIVAN