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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0059Z Jan 22, 2018)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
759 PM EST SUN JAN 21 2018

...VALID 01Z MON JAN 22 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
105 WSW O87 50 W O87 40 NW O87 35 NNE O87 35 E O87 35 N UKI
20 E UKI 15 NNW STS 35 W STS 85 W STS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SE JLN 10 ENE SGF 35 E SGF 25 WNW UNO 15 ENE FLP 25 WNW LZK
10 WNW M89 10 S TXK 4F4 10 SSW 3T1 10 E GVT 30 NW PRX 30 SSE MLC
30 S MKO 15 ENE TQH 30 SE JLN.


01Z UPDATE:

MADE ADDITIONAL MINOR ADJUSTMENTS BASED UPON RECENT RADAR AND
SATELLITE TRENDS...AS WELL AS HI-RES GUIDANCE.  REMOVED THE
NORTHERN EXTENT OF THE NORTHWEST CA MARGINAL AREA WHERE
PRECIPITATION IS EXPECTED TO CONTINUE TO SINK SOUTH THIS
EVENING...WITH RAINFALL RATES DECREASING AS ONSHORE FLOW WEAKENS. 
ACROSS THE SOUTHERN PLAINS...CONVECTION HAS DEVELOPED AS EXPECTED
ACROSS EASTERN TX AND OK INTO MO.  INDIVIDUAL CELLS HAVE REMAINED
PROGRESSIVE.  HOWEVER AS NOTED PREVIOUSLY...WITH CONVECTION
BRIEFLY TRAINING IN SOME LOCATIONS...THERE REMAINS A LOW END
THREAT FOR FLASH FLOODING.  THIS IS EXPECTED TO CONTINUE INTO THE
OVERNIGHT HOURS UNTIL AROUND 06Z WHEN CONVECTION IS FORECAST TO
PUSH PROGRESSIVELY TO THE WEST AHEAD OF THE UPSTREAM COLD FRONT.

PEREIRA

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