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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0058Z Sep 20, 2017)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
858 PM EDT TUE SEP 19 2017

...VALID 01Z WED SEP 20 2017 - 12Z WED SEP 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 E CWII 20 NW INL 15 SW GPZ 10 SE ILL 10 NNW PQN 20 E HON
45 NW ABR 30 SSW K9D7 15 SE CWZE 40 NNE CWOJ 40 E CWII.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 SSE HTO 30 SSE FOK 10 NNW FOK 10 SSE HFD 10 NW ORH
10 ENE LWM 45 NNE PVC 65 ENE PVC 80 E CQX 85 E ACK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 SSE MTP 15 SE HTO 10 WNW GON 10 SE ORH BVY 30 NE PVC
45 ENE CQX 60 E CQX 65 E ACK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSE CXWN 20 WSW ROX 10 SE TVF 25 NNE JKJ 10 SW JKJ 10 N KGWR
10 S JMS DVL 10 S CWNK 35 SSE CXWN.


2100 UTC UPDATE

INCLUDED A SLIGHT RISK ACROSS EASTERN ND AND FAR NORTHWEST
MN...BASED ON THE LATEST MESOANALYSIS AND HIGH-RES GUIDANCE
TRENDS...AS WELL AS THE RECENT SSEO 40KM NEIGHBORHOOD
PROBABILITIES OF 3 HOURLY QPF>FFG EXCEEDANCE CONSIDERING THE
CURRENT STATE OF THE SOIL MOISTURE/FFG. PLEASE REFER TO THE LATEST
MESOSCALE PRECIPITATION DISCUSSION OR MPD #813 FOR FURTHER
DETAILS.

ALSO TWEAKED THE MARGINAL AND SLIGHT RISK AREAS ACROSS EASTERN
LONG ISLAND-EASTERN NEW ENGLAND BASED ON THE LATEST QPF TRENDS PER
THE OPERATIONAL AND ENSEMBLE GUIDANCE (INCLUDING THE HIGH-RES
CAMS).

HURLEY


1500 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
CONFINED TO THE EASTERN PORTIONS OF THE NORTHERN PLAINS TOWARD THE
UPPER MS VALLEY.  THE PREVIOUS MARGINAL RISK AREA WAS EXTENDED
SLIGHTLY TO THE SOUTHEAST INTO FAR SOUTHEAST SD AND FAR SOUTHWEST
MN.  THIS WAS TO COVER THE SPREAD IN THE MODEL QPF ACROSS THESE
AREAS.

ORAVEC

INITIAL DISCUSSION

...HURRICANE JOSE CONTINUES TO LIFT NORTHWARD OVER THE WRN
ATLANTIC...


...SRN/SERN NEW ENGLAND...

WITH THE CONTINUED OFFSHORE APPROACH OF JOSE...WAA
PATTERN/WRAPPING TROPICAL MOISTURE WILL INCREASE RAINS ALONG
COASTAL SECTIONS OF SRN NEW ENGLAND SWWD BACK INTO PORTIONS OF THE
COASTAL NRN MID-ATLANTIC...WITH THE STRONGER ONSHORE FLOW
ESPECIALLY FAVORING AREAS FROM ERN LONG ISLAND INTO SE MA AS
RAINFALL EFFICIENCY/AMOUNTS INCREASE. A SLIGHT EWD SHIFT OF THE
NHC TRACK OF JOSE AND SATELLITE IMAGERY FAVORS TIGHTER
MOISTURE/PCPN GRADIENT ON ITS WRN PERIPHERY. THIS ALSO SEEMS TO BE
SUPPORTED BY GENERAL OFFSHORE MODEL TRENDS OF THE LAST FEW MODEL
CYCLES. EVEN SO...THERE REMAINS A SLIGHT RISK OF RUNOFF ISSUES
WITH EXCESSIVE RAINFALL OVER SERN NEW ENGLAND.


...NRN PLAINS/UPPER MIDWEST...

GUIDANCE REASONABLY AGREES THAT AN AMPLIFIED MID-UPPER TROUGH WILL
EJECT NEWD OVER THE N-CENTRAL US AS KICKER UPSTREAM S/WV ENERGY
AND POWERFUL JET DIGS FROM THE NE PACIFIC TO THE PACIFIC NW. A
LEAD FRONTAL SYSTEM WILL PUSH ACROSS THE N-CENTRAL US AS AMPLE
ENERGY ALOFT WORKS OVER THE REGION. MODELS SHOW STRONG RETURN SRLY
FLOW DEVELOPING IN RESPONSE INTO THE DAKOTAS/MN WHERE A NARROW
AXIS OF 1.5-1.75" PWS POOL INTO A REGION UNDER A COUPLED UPPER
JET. INCREASING LIFT AND INSTABILITY SHOULD COMBINE WITH TRIPLE
POINT ENHANCED FRONTAL CONVERGENCE TO SUPPORT SOME STRONG
CONVECTION AND A QUICK FEW INCHES OF RAIN THAT OFFERS A MARGINAL
RISK OF EXCESSIVE RAINFALL AND ASSOCIATED LOCAL RUNOFF ISSUES.

SCHICHTEL