Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 190824
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
324 AM EST SUN NOV 19 2017

...VALID 12Z SUN NOV 19 2017 - 12Z MON NOV 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NW UIL 35 WNW CWSP CWSP 15 SSE CLM 10 NNW SHN 25 WSW OLM
20 WNW TDO 10 WSW TDO TDO 15 ENE TDO 20 ENE TDO 30 ENE TDO
35 ENE TDO 40 E TDO 45 N CZK 30 N CZK 20 NNE CZK 10 E CZK
20 SE CZK 30 SSE CZK 40 S CZK 35 SE UAO 10 S TTD PDX 10 ENE SPB
10 SSE KLS 10 NNW SPB 15 W SPB 10 W HIO MMV 10 NW SLE 15 SW SLE
CVO 20 WSW CVO 25 S ONP 55 W ONP.


...PACIFIC NORTHWEST...

AS A POSITIVELY TILTED LONG WAVE TROUGH APPROACHES THE PACIFIC
NORTHWEST DURING DAY 1...SHORT WAVE ENERGY EJECTED FROM THE LONG
WAVE TROUGH INTERACTS WITH 1.25 INCH PRECIPITABLE WATER AIR
TRANSPORTED TO THE WA/OR COAST ON THE NOSE OF A 50/60 KNOT LOW
LEVEL SOUTHWEST FLOW. THERE IS A MULTI MODEL SIGNAL FOR THE BEST
LOW LEVEL MOISTURE CONVERGENCE TO OCCUR IN THE 20/00Z TO 20/06Z
TIME FRAME (WHEN THE MOISTURE FLUX IS EXPECTED TO PEAK BETWEEN
THREE AND FOUR STANDARD DEVIATIONS ABOVE THE MEAN). THE STRONG
UPSLOPE FLOW...COUPLED WITH SYNOPTIC SCALE ASCENT IN THE LEFT
FRONT QUADRANT OF A 110 KNOT JET STREAK APPROACHING THE OR
COAST...SHOULD BE SUFFICIENT TO PRODUCE AXES OF 2.50 TO 4.00
INCHES OF QPF IN THE FAVORED UPSLOPE REGIONS...WITH THE HIGHEST
AMOUNTS ACROSS THE HIGHER TERRAIN OF THE WA OLYMPIC RANGE (WHICH
IS FAVORED IN THE LOW LEVEL SOUTHWEST FLOW).

HOURLY RAINFALL RATES IN EXCESS OF 0.50 INCHES COULD BEGIN ACROSS
PORTIONS OF WA/OR AS EARLY AS 20/00Z...BUT GIVEN THE TIMING OF THE
BEST LOW LEVEL MOISTURE AND UPSLOPE FLOW...THE BEST THREAT FOR
HIGHER RAINFALL RATES SHOULD OCCUR BETWEEN 20/00Z AND 20/06Z
(COINCIDING WITH THE BEST LOW LEVEL MOISTURE FLUX). THE MOISTURE
PLUME DROPS SOUTH AS THE LONG WAVE TROUGH REACHES THE COAST AFTER
20/06Z...WITH THE HIGHEST RAINFALL RATES MOVING INTO FAVORED
UPSLOPE AREAS OF OR.

AFTER COLLABORATING WITH WFO SEW...A MARGINAL RISK AREA WAS
EXTENDED FROM THE OLYMPIC RANGE IN WA INTO THE OR COASTAL
RANGE...AS WELL AS THE SOUTHERN WA/NORTHERN OR CASCADES FOR DAY 1.

HAYES
$$




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