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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0819Z Nov 22, 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
319 AM EST WED NOV 22 2017

...VALID 12Z WED NOV 22 2017 - 12Z THU NOV 23 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NNW CWZA 10 N CWZA 10 SSE CWZA 25 S CWZA 35 ENE BVS
35 ENE AWO 40 E AWO 25 NNE SMP 15 ENE SMP 15 ESE SMP 30 SSE SMP
35 W YKM 45 WSW YKM 25 NNW DLS 15 E CZK 15 W DLS 15 S CZK
15 ESE TTD TTD 20 NNE PDX 25 E KLS 25 E TDO 25 SE TCM 10 SE RNT
15 SE PAE 10 SE AWO BVS 10 S BLI 10 E ORS ORS CWZO CWDR
15 SSE CWDR 20 SW NUW 25 SSW NUW 20 W PAE 20 N PWT PWT 10 S PWT
10 W TIW 15 ESE SHN 10 WSW OLM 15 SW OLM 10 NW TDO 10 SW TDO
10 NW KLS 10 WNW SPB 15 W SPB 15 WNW HIO MMV 15 W SLE CVO
10 WSW EUG 20 SW EUG 30 NE OTH 15 NNE OTH 20 NNW OTH 40 NNW OTH
40 WSW ONP.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NW UIL 25 N UIL 10 SSW CWSP 10 NW CLM CLM 20 SE CLM
25 NW PWT 15 N SHN HQM 40 WSW HQM.


...PACIFIC NORTHWEST...

THE CURRENT SHOT OF DEEPER ATMOSPHERIC MOISTURE IS EXPECTED TO
CLEAR THE PACIFIC NORTHWEST AND NORTHERN ROCKIES DURING THE FIRST
PART OF DAY 1. HOWEVER...THE MOST RECENT IR IMAGES SHOWED THE NEXT
SLUG MOISTURE RIDING NORTHWARD FROM NEAR 32N 133W...WHERE THE
BLENDED TPW PRODUCT SHOWED PRECIPITABLE WATER VALUES BETWEEN 1.50
AND 2.00 INCHES. THE ONSHORE FLOW WILL CONTINUE TO PRODUCE UPSLOPE
CONDITIONS ACROSS THE PACIFIC NORTHWEST... WITH RAINFALL RATES
INCREASING AFTER 23/00Z...AS SHORT WAVE ENERGY EJECTED FROM THE
LONG WAVE TROUGH APPROACHES THE PACIFIC NORTHWEST. THERE WAS A
MULTI MODEL SIGNAL FOR HOURLY RAINFALL RATES TO INCREASE TO 0.50
INCHES OR GREATER IN THE 23/06Z TO 23/12Z TIME FRAME...AS A 40
KNOT LEVEL SOUTHWEST FLOW TRANSPORTS 1.00 INCH PRECIPITABLE WATER
ACROSS WESTERN WA. 
 
THE INCREASED MOISTURE AND UPSLOPE FLOW IS EXPECTED TO RESULT IN
LOCAL 3.00 TO 4.00 INCH QPF AMOUNTS CENTERED ON THE WA OLYMPIC
RANGE (WHICH IS FAVORED IN THE SOUTHWEST FLOW REGIME). SINCE THIS
AREAS HAS SEEN HEAVY RAINFALL OVER THE PAST COUPLE OF DAYS...THE 
ADDITIONAL RAINFALL RAISES THE POTENTIAL FOR ROCK SLIDES AND LAND
SLIDES IN FAVORED LOCATIONS. A SLIGHT RISK AREA WAS PLACED HERE
FOR DAY 1 TO ACCOUNT FOR THE ELEVATED FLOOD THREAT. 
 
THE LOW LEVEL SOUTHWEST FLOW ALSO TARGETS THE WA CASCADES...WHERE
THE COMBINATION OF UPSLOPE FLOW AND SYNOPTIC SCALE ASCENT IS
EXPECTED TO PRODUCE 1.75 TO 2.25 INCHES OF QPF...WITH THE HIGHEST
AMOUNTS OVER THE NORTHERN WA CASCADES. SNOW LEVELS REMAIN ELEVATED

ACROSS THE WA CASCADES...SO ALMOST ALL OF THE QPF IS EXPECTED TO
BE IN THE FORM OF RAINFALL. WITH THIS IN MIND...A MARGINAL RISK
WAS EXTENDED HERE TO COVER THE FLOOD THREAT. 

HAYES