Quantitative Precipitation Forecast
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FOUS30 KWBC 171417
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
916 AM EST TUE JAN 17 2017

...VALID 15Z TUE JAN 17 2017 - 12Z WED JAN 18 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW CWZA 25 S CWZA 40 SSE CWZA 35 ENE AWO 35 ESE AWO
10 NW SMP 15 WSW SMP 30 SW SMP 45 SE TCM 50 E TDO 40 NNE CZK
25 NNE CZK 15 NNE CZK CZK 15 SSE CZK 30 S CZK 40 ESE UAO
50 NW RDM 45 WNW RDM 50 E CVO 35 E CVO 25 SE SLE 15 SSE UAO
15 NE UAO PDX 15 ENE KLS 15 ENE TDO 20 SSE GRF TCM 10 NE RNT
15 NNE AWO CWMM.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 NW UIL 35 NNW UIL 10 SW CWSP 15 SSE CWSP 15 ESE CLM
20 NNW PWT PWT 10 SW PWT 10 WNW OLM 20 SSW OLM 10 W TDO
10 WNW KLS 20 SW KLS 10 W HIO 15 W SLE 10 W CVO 15 WSW EUG
15 SE OTH 35 ENE CEC 25 ESE CEC 30 SSW CEC.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE BQP 30 S MLU 10 NNW POE 30 NW BPT EFD 15 ENE 5R5
35 SSE 3T5 15 WSW 3T5 10 W 62H 20 SSW LHB 15 NW LHB 30 S CRS TYR
30 SSE TXK 20 NE ELD 25 S LLQ 20 ESE BQP.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSW CLM 25 WNW PWT 10 NNW SHN 15 ENE HQM 15 NW HQM
30 SSE UIL 15 SE UIL 25 ESE UIL 20 SSW CLM.


15 UTC UPDATE...OPT TO MAINTAIN WPC CONTINUITY FROM OUR PREVIOUS
ISSUANCE BUT WILL CONTINUE TO MONITOR LATEST MODEL AND RADAR
TRENDS.

SCHICHTEL


...PACIFIC NORTHWEST...

THE LATEST CIRA-LPW DATA AND AMSU 89 GHZ DATA CONFIRMS WHAT IS AN
IMPRESSIVELY LONG-FETCHED ATMOSPHERIC RIVER THAT EXTENDS FROM JUST
OFFSHORE SOUTHERN BRITISH COLUMBIA ALL THE WAY BACK TO THE
SOUTHWEST INTO THE TROPICAL WESTERN PACIFIC OCEAN WITH MULTIPLE
SURFACE WAVES RIDING ALONG IT. THIS ATMOSPHERIC RIVER WILL BE
MOVING INTO THE PACIFIC NORTHWEST LATER ON TUESDAY AND CONTINUING
INTO WEDNESDAY. AFTER A PERIOD OF GENERALLY LIGHT WARM ADVECTION
PRECIPITATION INITIALLY ACROSS THE OLYMPIC PENINSULA AND THE
NORTHERN WA CASCADES...THE LATEST GUIDANCE AGREES IN BRINGING MUCH
STRONGER DEEP LAYER SOUTHWEST ONSHORE FLOW INTO THE COASTAL RANGES
OF WA/OR AND INTO THE CASCADES TUESDAY NIGHT AHEAD OF AN
APPROACHING COLD FRONT. THIS WILL RESULT IN THE ARRIVAL OF
CONSIDERABLY STRONGER MOISTURE FLUX AND PW ANOMALIES. A SOUTHWEST
LOW LEVEL JET OF 50 TO 70 KTS IS FORECAST TUESDAY NIGHT JUST
OFFSHORE WA/OR WHICH WILL FOSTER 850/700 MB MOISTURE FLUX
ANOMALIES OF 4 TO 5 STANDARD DEVIATIONS ABOVE THE MEAN...AND PW
VALUES OF 2 TO 2.5 STANDARD DEVIATIONS ABOVE THE MEAN. THIS WILL
RESULT IN HEAVY OROGRAPHICALLY ENHANCED RAINS FOR THE COASTAL
RANGES AND ESPECIALLY OVER THE OLYMPIC PENINSULA WHERE AS MUCH AS
3 TO 6 INCHES OF RAIN WILL BE POSSIBLE BY WEDNESDAY MORNING. THIS
WILL RESULT IN SOME HEIGHTENED CONCERNS FOR RUNOFF PROBLEMS WITH
DEBRIS FLOWS AND MUDSLIDES NOT OUT OF THE QUESTION. SOMEWHAT
LESSER BUT ALSO HEAVY RAINFALL AMOUNTS OF 2 TO 4 INCHES ARE
EXPECTED IN THE FOOTHILLS OF THE WA AND NORTHERN OR CASCADES AS
WELL. THE DEEP LAYER PACIFIC MOISTURE PLUME SHOULD SETTLE AS FAR
SOUTH AS THE SOUTHWEST OR COASTAL RANGES AND EXTREME NORTHWEST CA
BY WEDNESDAY MORNING.

...SOUTHEAST TX...NORTHWEST LA...FAR SOUTHERN AR...

IN THE WAKE OF THE DEPARTING SHORTWAVE TROUGH AND SURFACE WAVE
MOVING THROUGH THE LOWER GREAT LAKES AND NORTHEAST WILL BE A
TRAILING COLD FRONT THAT WILL EXTEND DOWN ACROSS THE TN VALLEY AND
SOUTHWEST BACK TO THE LOWER MS VALLEY AND SOUTHEAST TX COASTAL
PLAIN. THE PORTION OF THE FRONT INVOLVING SOUTHEAST TX/LA IS
EXPECTED TO STALL OUT BY LATER TUESDAY AND THE GUIDANCE SUPPORTS
THE DEVELOPMENT OF A WAVE OF LOW PRESSURE ALONG IT BY TUESDAY
EVENING. THIS WILL BE IN RESPONSE TO AN ELONGATED
POSITIVELY-TILTED TROUGH AND CLOSED LOW BACK TOWARD THE SOUTHERN
HIGH PLAINS AND THE FOUR CORNERS REGION THAT WILL ALLOW SOME WEAK
SHORTWAVE ENERGY TO EJECT DOWNSTREAM ACROSS THE SOUTHERN PLAINS
AND THEN INTERACT WITH THE FRONT. THE MODELS AGREE IN DEVELOPING A
BROAD AREA OF FAVORABLE RIGHT-ENTRANCE REGION JET DYNAMICS BY
LATER TUESDAY AND EARLY WEDNESDAY AS WELL. GIVEN THE INCREASED
LARGE SCALE ASCENT AND INCREASED POOLING OF MOISTURE AND AT LEAST
MODEST INSTABILITY OF 1000 TO 1500 J/KG OF MUCAPE OVER SOUTHEAST
TX...THE FRONTAL ZONE IS EXPECTED TO BECOME CONVECTIVELY ACTIVE
WITH SOME SLOW-MOVING AND HEAVY SHOWERS AND THUNDERSTORMS. THE
HIGHEST PW VALUES SHOULD BE ACROSS SOUTHEAST TX AND WESTERN LA
WITH A POOL OF OVER 1.5 INCH PWS WITH THE AID OF A S/SW LOW LEVEL
JET OF 30 TO 40 KTS IN OFF THE FAR WESTERN GULF OF MEXICO. THIS
WILL HELP ENSURE HEAVIER RAINFALL RATE POTENTIAL AND ESPECIALLY
WITH THE AFOREMENTIONED INSTABILITY POOLING NEAR THE TAIL END OF
THE FRONT. THE NON-NCEP MODELS COLLECTIVELY ALONG WITH THE HIRES
ARW/NMMB MODELS SUPPORT SOME HEAVY RAINS ACROSS THIS AREA...WITH 1
TO 2 INCH RAINFALL AMOUNTS AND ISOLATED TOTALS PERHAPS OVER 3
INCHES GIVEN THE EXPECTED SLOW MOVEMENT AND POTENTIAL FOR SOME
TRAINING CONVECTION LOCALLY. THEREFORE SOME ISOLATED RUNOFF
PROBLEMS WILL BE POSSIBLE AS A RESULT.

ORRISON
$$





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