Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
000
FOUS30 KWBC 200109
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
808 PM EST SUN NOV 19 2017

...VALID 01Z MON NOV 20 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
45 WNW UIL 30 WNW CWSP CWQK 15 ESE CLM 10 NW PWT 10 ESE SHN
15 SSE OLM 30 ENE TDO 45 NNW DLS 10 S DLS 15 NNW RDM 40 SW RDM
45 ESE EUG 30 ESE CVO 15 E SLE PDX 10 NNW SPB 15 W SPB
10 WNW SLE 20 NW EUG 35 WSW EUG 20 NW OTH 55 WNW OTH 100 WNW OTH.


01Z UPDATE...

NO SIGNIFICANT CHANGES TO THE PREVIOUS THINKING...PLEASE CONSULT
MPD #937 FOR THE LATEST ON THE ATMOSPHERIC RIVER CONDITIONS
IMPACTING THE PACIFIC NORTHWEST.

ORRISON


...PACIFIC NORTHWEST...

IN THE 15Z UPDATE A MARGINAL RISK OF EXCESSIVE RAINFALL REMAINS
FOR THE AFTERNOON AND OVERNIGHT PERIOD IN WESTERN WASHINGTON AND
OREGON. WE EXPANDED THE RISK AREA SOUTHWARD JUST VERY
MINIMALLY...ABOUT 30 MILES...ALONG BOTH THE COASTAL RANGES AND THE
CASCADES...OWING TO THE SOUTHWARD EXTENT OF DEEP FORCING AND
ONSHORE FLOW IN OUR PREFERRED GFS/CMC SOLUTION...ALTHOUGH WE DID
NOT TAKE THE QPF DETAILS FROM THOSE TWO MODELS. IT APPEARED
SEVERAL OF THE HI-RES MODELS MET OUR EXPECTATIONS...AND THOSE SUCH
AS THE NSSL WRF BRING RAIN RATES APPROACHING A HALF INCH PER HOUR
DOWN TO ABOUT HIGHWAY 20 IN THE CASCADES AND TO SEAROSE BEACH
ALONG THE COAST BY 12Z MONDAY.

PREVIOUS DISCUSSION...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/BURKE
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.