Quantitative Precipitation Forecast
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FOUS30 KWBC 180849
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 AM EST WED JAN 18 2017

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


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SE KXIH 20 NNW KGVX 25 WNW KBQX 25 ENE KRP 20 WSW VCT
15 SSW 3T5 20 W 62H 25 NW LHB 30 S CRS 25 NNW PSN 10 ESE 3T1
20 S DEQ 15 SW HOT 25 W LZK 10 NNW LRF 30 SSE M19 20 SE JBR
25 SE HKA 20 SSW MKL 35 N TUP 15 WNW TUP 35 ENE GWO 40 N HKS
30 SW TVR 30 SE ESF 35 WNW 7R4 20 W KCMB 15 SSW KVBS 10 SE KXIH.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NW ONP 30 NW S47 25 SSE AST 25 WSW MMV 20 SW CVO 20 NNW RBG
15 N SXT 15 SSE SXT 30 W SIY 30 SW SIY MHS 20 SE MHS 25 NE RDD
30 NE CIC 30 ENE OVE 25 SW TVL 45 WNW MMH 30 ENE MCE 10 NNE MHR
25 W MYV 10 W VCB 10 SSW SUU OAK 10 NE WVI 30 ESE SNS 25 NNE 87Q
15 SE PRB 25 NE SMX 30 NNE SBA 10 NNW 3A6 CQT 25 SSE NTD
45 NW NSI 75 SSW LPC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE TYR 40 NW SHV 30 ESE TXK 25 NNW ELD 20 SSW PBF 35 NE LLQ
15 N GLH 20 SE BQP 15 W ACP 20 WNW LCH 20 SSW BPT 25 NNE KXIH
LVJ 15 E 5R5 20 NNW 5R5 30 SSE 11R 25 ENE 11R 15 WNW CLL
15 NE LHB 20 S PSN 20 ESE TYR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 WNW CEC 55 NNW CEC 50 SSW OTH 25 WSW SXT 35 E CEC 30 NW O54
25 NNE O54 20 ENE O54 15 SSW O54 35 SSW O54 35 NE UKI 25 SE UKI
10 NE STS 25 SSW STS 50 WSW STS 65 W STS.


...EASTERN TEXAS/LOWER MISSISSIPPI VALLEY...

THE TAIL END OF A FRONTAL ZONE STALLED OUT OVER SOUTHEAST TX AND
THE LOWER MS VALLEY WILL BE THE FOCUS FOR NUMEROUS SHOWERS AND
THUNDERSTORMS THIS PERIOD...WITH HEAVY TO POSSIBLY EXCESSIVE
RAINFALL EXPECTED AS A DEEP LAYER POOL MOISTURE AND AT LEAST
MODEST INSTABILITY POOLS ALONG THE FRONT. MEANWHILE...FAVORABLE
RIGHT-ENTRANCE REGION JET DYNAMICS ARE EXPECTED TO BE IN PLACE
OVER THIS REGION DOWNWIND OF A BROAD UPPER TROUGH AND CLOSED LOW
OVER THE SOUTHERN HIGH PLAINS AND THE FOUR CORNERS REGION. BY
LATER WEDNESDAY NIGHT AND EARLY THURSDAY THE UPSTREAM TROUGH WILL
BE ADVANCING EAST AND BECOMING MORE NEUTRALLY TILTED AS IT EJECTS
EAST TOWARD ACROSS THE SOUTHERN PLAINS. THIS WILL ALLOW FOR SOME
STRENGTHENING OF THE JET FORCING/LARGE SCALE ASCENT OVER SOUTHEAST
TX AND INTO SOUTHWEST LA IN VICINITY OF THE FRONT. PWATS ARE
FORECAST TO RISE TO NEAR 1.75 INCHES OVER THIS AREA WITH THE HELP
OF A 30 KT S/SW LOW LEVEL JET ADVANCING IN OFF THE GULF OF MEXICO.
IN ADDITION...THE CIRA-LPW PRODUCT SHOWS A WELL-DEFINED
SUBTROPICAL MOISTURE TAP COMING NORTHEAST ACROSS MEXICO FROM THE
EASTERN PACIFIC OCEAN IN THE 700/300 MB LAYER WHICH WILL BE
FOSTERING WARMER RAIN PROCESSES THAT WILL ENCOURAGE HEAVIER
RAINFALL RATES. THE MEAN LAYER FLOW WILL TEND TO BE NEARLY
PARALLEL THE FRONT...AND WITH THE PERSISTENT LEVEL OF LARGER SCALE
FORCING...LOW LEVEL CONVERGENCE ALONG THE FRONT AND FAVORABLE
THERMODYNAMICS...THERE WILL LIKELY BE AN AXIS OF BACKBUILDING AND
TRAINING CONVECTION. THE NAM/GFS AND ECMWF MAY BE TENDING THE
FOCUS THEIR HEAVIER RAINFALL POTENTIAL A BIT TOO FAR NORTH AWAY
FROM THE BETTER INSTABILITY AXIS...AND AS A RESULT KEPT THE FOCUS
OF THE HEAVIEST RAINS JUST A BIT FARTHER SOUTH OVER FAR EASTERN TX
AND WESTERN LA WHICH IS A BIT CLOSER TO THE HIRES MODEL CONSENSUS.
RAINFALL AMOUNTS OF AS MUCH AS 3 TO 4 INCHES WITH ISOLATED HEAVIER
AMOUNTS WILL BE POSSIBLE THIS PERIOD.

...PACIFIC NORTHWEST/CALIFORNIA INTO THE GREAT BASIN/NORTHERN
ROCKIES...

STRONG ATMOSPHERIC RIVER CONDITIONS WILL BE WELL UNDERWAY ACROSS
THE PACIFIC NORTHWEST EARLY WEDNESDAY WITH HEAVY RAIN AND HIGH
ELEVATION SNOW...AND THIS SHOULD GRADUALLY ADVANCE SOUTH DOWN
ACROSS NORTHERN AND CENTRAL CA THROUGH WEDNESDAY NIGHT AND EARLY
THURSDAY AS A COLD FRONT SETTLES SOUTHEAST ACROSS THE REGION. THE
LATEST CIRA-LPW AND AMSU 89 GHZ DATA CONTINUES TO SHOW AN
ORIENTATION OF THIS ATMOSPHERIC RIVER THAT EXTENDS IMPRESSIVELY
WELL SOUTHWEST ALL THE WAY BACK TO THE TROPICAL WESTERN PACIFIC
OCEAN. PWS IN THE 700/500 MB LAYER ARE QUITE HIGH AND WILL BE
AIMED NEARLY ORTHOGONAL INTO ESPECIALLY THE SOUTHWEST OR/NORTHWEST
CA COASTAL RANGES BY LATE WEDNESDAY AND THEN DOWN INTO CENTRAL CA
AND THE CENTRAL/NORTHERN SIERRA-NEVADA THROUGH EARLY THURSDAY.
ENHANCED MOISTURE FLUX AND PW ANOMALIES WILL BE IN PLACE GIVEN THE
STRONG LOW TO MID LEVEL WIND FIELD AND UPSTREAM MOISTURE FEED. IN
FACT...A SOUTHWEST LOW LEVEL JET UPWARDS OF 70 KTS IS FORECAST
ACROSS SOUTHWEST OR AND NORTHWEST CA WHICH WILL FOSTER 850/700 MB
MOISTURE FLUX ANOMALIES OF 4 TO 5 STANDARD DEVIATIONS ABOVE THE
MEAN...AND PW VALUES OF 2 TO 3 STANDARD DEVIATIONS ABOVE THE MEAN.
THE HEAVIEST RAINS WILL BE IN PLACE ACROSS THESE AREAS WHERE AS
MUCH AS 4 TO 8 INCHES OF RAIN IS POSSIBLE. THIS WILL LIKELY CAUSE
CONCERNS FOR RUNOFF PROBLEMS INCLUDING DEBRIS FLOWS AND MUDSLIDES
NEAR ANY BURN SCAR AREAS. THESE AREAS WILL BE SUSCEPTIBLE TO FLASH
FLOODING IN PARTICULAR. SOMEWHAT LESSER AMOUNTS OF 2 TO 4 INCHES
WILL BE EXPECTED DOWN ACROSS THE CENTRAL CA COASTAL RANGES AND
INTO THE FOOTHILLS OF THE NORTHERN/CENTRAL SIERRA-NEVADA WITH
ISOLATED HEAVIER AMOUNTS. RUNOFF PROBLEMS HERE WILL ALSO AGAIN BE
A CONCERN AND ESPECIALLY WITH SUCH WET ANTECEDENT CONDITIONS.
FARTHER SOUTH TOWARD SOUTHERN CA THERE WILL BE AN INCREASE IN
ONSHORE FLOW LATE IN THE PERIOD AND SOME LOCALLY HEAVY RAINS MAY
APPROACH THE COASTAL RANGES HERE BY EARLY THURSDAY. WILL NEED TO
MONITOR FUTURE SHORT RANGE TRENDS FOR SOUTHERN CA FOR SENSITIVE
BURN SCAR AREAS AS THE DEEP MOISTURE PLUME TO THE NORTH ALONG WITH
THE FRONT ARRIVES.

ORRISON
$$





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