Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

000
FOUS30 KWBC 180739
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
339 AM EDT WED OCT 18 2017

...VALID 12Z WED OCT 18 2017 - 12Z THU OCT 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 W UIL 45 NNW UIL 20 W CWSP 10 ESE CLM 20 N PWT 10 WNW BFI
TIW 10 NW GRF OLM 20 SE OLM 25 SSE GRF 25 SE TCM 15 ESE TCM
20 SE SEA RNT 20 ESE PAE 10 ESE AWO 10 SE BLI CYXX CWZA CYHE
15 WSW CWPR 25 SSE CWPR 30 W CWYY 25 N KS52 15 NW KS52 10 W KS52
15 SSW KS52 25 S KS52 25 SSW KS52 30 SSW KS52 35 N EAT
30 NNW EAT 40 NW EAT 30 WNW EAT 25 W EAT 15 ENE SMP SMP
15 SW SMP 25 SW SMP 25 SSW SMP 25 S SMP 35 WSW ELN 35 WNW YKM
40 W YKM 35 W YKM 40 WSW YKM 45 WSW YKM 50 W YKM 50 E TDO
45 E TDO 50 N CZK 45 WSW YKM 40 N DLS 35 NNW DLS 40 NNE CZK
35 NNE CZK 30 NNE CZK 20 NE CZK 15 NE CZK 10 NNE CZK 15 N CZK
10 NNW CZK CZK 10 W CZK 10 NNE TTD 20 NNE VUO 10 ESE KLS KLS
10 WNW KLS 15 WSW KLS 25 ESE AST 25 W SPB 20 WNW HIO 20 E S47
15 NW MMV 15 SE S47 25 WSW MMV 25 W SLE 25 NW CVO 20 NE ONP
30 N ONP 40 WNW S47.


...PACIFIC NORTHWEST...

FLAT SHORTWAVE UPPER RIDGE AXIS WILL PUSH EAST OF THE NORTHERN
ROCKIES LATER TODAY...GIVING WAY TO AN AMPLIFYING UPPER TROUGH
THAT WILL APPROACH THE PAC NW COAST ON THU. INCREASING UPPER LEVEL
DIFFLUENCE AND DEEP-LAYER MOIST ISENTROPIC ASCENT WITHIN THE WARM
CONVEYOR BELT (WCB) AHEAD OF THE AMPLIFYING TROUGH WILL DIRECT AN
ATMOSPHERIC RIVER/ELONGATED PLUME OF DEEP-LAYER MOISTURE INTO
WESTERN WA AND EVENTUALLY WESTERN OR WEDNESDAY AND WEDNESDAY
NIGHT. SOUTHWESTERLY 850 MB FLOW INCREASING TO ~50 KTS WILL LEAD
TO ROBUST LOW-LEVEL MOISTURE TRANSPORT INTO THE COASTAL AND
CASCADE RANGES...WITH 850 MB MOISTURE FLUX ANOMALIES EXPECTED TO
TOP OUT BETWEEN 4-5 STANDARD DEVIATIONS ABOVE NORMAL ACROSS
WESTERN WA AND FAR NORTHWEST OR PER THE SREF AND GEFS.

IN ADDITIONAL TO THE FAVORABLE DYNAMICAL SETUP AND MOISTURE
PROFILE AHEAD OF THE TROUGH...STRENGTHENING RIGHT ENTRANCE REGION
FORCING VIA THE BUCKLING UPPER JET STREAK THAT WILL DROP SOUTH OF
B.C. AND INTO THE PAC NW LATER TODAY/TONIGHT WILL ENHANCE THE
DEEP-LAYER ASCENT AND LOW LEVEL FRONTOGENESIS. THIS WILL LIKELY
COMPOUND PCPN TOTALS OVER THE FAVORED HIGHER TERRAIN (WESTERN
SLOPES) OF THE COASTAL-CASCADE RANGES WED-WED NIGHT AS THE
GUIDANCE OF LATE HAS CONSISTENTLY SHOWN. TO THAT END...CONSIDERING
THE PROLIFIC TOTALS...CHANGES TO THE QPF FROM CONTINUITY (PREVIOUS
WPC FORECAST) WERE NEGLIGIBLE...WHICH YIELDED 5KM AREAL-AVERAGE
TOTALS OF 6-8 INCHES ACROSS THE OLYMPICS AND 3-5 INCHES OVER THE
NORTHERN WA CASCADES. LESSER AMOUNTS (1-3") WERE NOTED ACROSS THE
SOUTHERN WA COASTAL-CASCADE RANGES ALONG WITH THE NORTHERN OR
COASTAL MTNS. THE LACK (ABSENCE) OF DEEP-LAYER INSTABILITY WILL
INHIBIT SHORT-TERM RAINFALL RATES AND THUS LIMIT THE RISK OF FLASH
FLOODING...HOWEVER...THE VOLUME OF RAINFALL EXPECTED COULD VERY
WELL LEAD TO SOME LONGER DURATION RUNOFF ISSUES LATER IN THE
PERIOD (LATE WED-WED NIGHT) AS THE SOIL CONTINUES TO SATURATE.

HURLEY

$$




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