815  
FOUS30 KWBC 221416  
QPFERD  
 
EXCESSIVE RAINFALL DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
916 AM EST WED NOV 22 2017  
   
..VALID 15Z 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 20 SW MMV CVO  
20 WSW RBG 15 E CEC 50 W CEC 105 WNW CEC.  
 
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.  
 
1500 UTC UPDATE  
 
NO CHANGES MADE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL  
OUTLOOK.  
 
ORAVEC  
 
INITIAL DISCUSSION  
   
..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  

 
 
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