Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 211457
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
956 AM EST SUN JAN 21 2018

...VALID 15Z SUN JAN 21 2018 - 12Z MON JAN 22 2018...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 WNW CEC 70 SW OTH 40 S OTH 30 WNW SXT 10 WSW SXT 35 SW MFR
30 W O54 30 WSW O54 45 WSW RBL 20 E UKI 15 NNW STS 35 W STS
70 SW UKI.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 E SGF 15 WSW UNO 40 S FLP HOT 10 S TXK 4F4 25 ESE TRL
15 E TKI 15 E DUA 20 ESE MLC 20 SW JSV 20 NNE JSV SLG 35 NW HRO
15 SE SGF 30 E SGF 40 E SGF.


15Z UPDATE:

MADE SOME MINOR TWEAKS TO THE MARGINAL RISK AREA OVER THE SOUTHERN
PLAINS/LOWER MS VALLEY. STILL ANTICIPATING A MARGINAL FLASH FLOOD
THREAT TO EXIST BETWEEN ABOUT 21Z THIS AFTERNOON THROUGH 06Z
TONIGHT. CONVECTION MAY BRIEFLY TRAIN IN THE INITIATION PHASE OF
CONVECTION THROUGH THIS PERIOD...ALLOWING FOR THE POSSIBILITY OF A
FEW LOCATIONS APPROACHING FLASH FLOOD GUIDANCE. THE ADJUSTMENT WAS
TO NUDGE THE THE WESTERN EXTENT OF THE MARGINAL RISK A BIT FURTHER
WEST TO INCLUDE MORE OF SOUTHEAST OK AND NORTHEAST TX. THIS IS
BASED ON RECENT HRRR AND EXPERIMENTAL HRRR RUNS AND THE IDEA THAT
CAMS SEEM TO UNDER DO RAINFALL AMOUNTS NEAR THE AXIS OF CONVECTIVE
INITIATION...RESULTING IN THE CAMS BEING A BIT TOO FAR EAST WITH
QPF MAXIMUMS DURING THIS INITIATION PHASE. -CHENARD


PREVIOUS DISCUSSION...


NORTHEAST TX---FAR SOUTHEAST OK INTO WESTERN ARKANSAS

PRECIPITATION EXPECTED TO BECOME INCREASINGLY ACTIVE TO THE
SOUTHEAST OF THE STRONG EJECTING CENTRAL PLAINS CLOSED LOW---ALONG
AND AHEAD OF THE ASSOCIATED COLD FRONT PUSHING EAST FROM THE
EASTERN PORTIONS OF THE SOUTHERN PLAINS LATE SUNDAY AFTERNOON TO
THE LOWER MS VALLEY REGION BY EARLY MONDAY.  INSTABILITY WILL BE
PEAKING ALONG AND AHEAD OF THE FRONT IN THE 0000 TO 0600 UTC TIME
FRAME FROM EASTERN PORTIONS OF THE SOUTHERN PLAINS---NORTHEASTWARD
TO THE LOWER MO VALLEY/MID MS VALLEY REGION.  EXPECT A WELL
DEFINED FRONTAL/PRE-FRONTAL CONVECTIVE LINE TO STRETCH FROM
NORTHEAST TX INTO FAR SOUTHEAST OK---WESTERN ARKANSAS INTO SOUTH
CENTRAL MO IN THE 0000-0600 UTC TIME FRAME.  THIS PERIOD WILL HAVE
THE GREATEST PRECIP POTENTIAL AS THE DEVELOPING CONVECTIVE LINE
WILL BE SLOWER MOVING WITH SOME POTENTIAL FOR A SMALL PERIOD OF
TRAINING OF CELLS IN A SOUTHWEST TO NORTHEAST DIRECTION FORM
NORTHEAST TX INTO FAR SOUTHEAST OK---WESTERN AR.  SHORTLY PRIOR TO
0600 UTC AND AFTERWARD---THIS CONVECTIVE LINE IS EXPECTED TO
BECOME MORE PROGRESSIVE---LOWERING THE PRECIP POTENTIAL TOWARD THE
LOWER TO MIDDLE MS VALLEY REGION.  HOURLY RAINFALL RATES OF
1.00-1.5" POSSIBLE IN THE 0000-060O UTC TIME PERIOD FROM NORTHEAST
TX INTO FAR SOUTHEAST OK AND WESTERN AR WHERE ISOLATED RUNOFF
ISSUES MAY DEVELOP.  THE PREVIOUS MARGINAL RISK AREA WAS NARROWED
SLIGHTLY ON THE EASTERN END TO REFLECT THE EXPECTED MORE
PROGRESSIVE NATURE OF THE CONVECTIVE LINE AFTER 0600 UTC.

FAR SOUTHWEST OREGON INTO NORTHWEST CALIFORNIA

CONCERNS FOR ISOLATED RUNOFF ISSUES WILL BE ACROSS BURN SCAR AREAS
OF FAR SOUTHWEST OREGON LATE SUNDAY MORNING INTO EARLY AFTERNOON
AND ACROSS NORTHWEST CALIFORNIA SUNDAY AFTERNOON INTO SUNDAY
NIGHT.  STRONG NORTHEAST PACIFIC HEIGHT FALLS PUSHING INTO
PACIFIC NORTHWEST ON SUNDAY WILL SUPPORT THE SOUTHEAST PUSH OF A
WELL DEFINED SURFACE FRONT INTO THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA AREA SUNDAY AFTERNOON/NIGHT.  AN ORGANIZED AREA OF
HEAVY PRECIP LIKELY ALONG AND AHEAD OF THIS FRONT AFFECTING AREAS
FROM THE WASHINGTON/OREGON CASCADES---WEST TO THE COAST RANGES AND
SOUTH INTO NORTHWEST CALIFORNIA.  WHILE THIS FRONT IS EXPECTED TO
BE PROGRESSIVE AND PW VALUES ONLY NEAR SEASONAL NORMS---THE STRONG
ONSHORE SOUTH SOUTHWEST LOW LEVEL FLOW WILL HAVE A SIGNIFICANT
UPSLOPE COMPONENT OVER FAR SOUTHWEST OREGON INTO NORTHWEST
CALIFORNIA.  HOURLY PRECIP RATES IN THE .25"+ RANGE POSSIBLE OVER
FAR SOUTHWEST OREGON LATE SUNDAY MORNING-EARLY AFTERNOON AND OVER
NORTHWEST CALIFORNIA SUNDAY AFTERNOON INTO SUNDAY NIGHT.  THE
PREVIOUS MARGINAL RISK AREA WAS MAINTAINED FOR POTENTIAL
RUNOFF/DEBRIS FLOW ISSUES OVER RECENT BURN SCAR AREAS OF SOUTHWEST
OREGON INTO NORTHWEST CALIFORNIA.

ORAVEC

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