Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 171117
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
715 AM EDT WED SEP 17 2014

...VALID 12Z WED SEP 17 2014 - 12Z THU SEP 18 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW SJN 20 SE GNT 25 SSE 4MY 25 ENE 4CR 50 NE ROW 55 W LBB
7F9 15 SE PWG 15 NNW 62H AUS 25 N JCT 45 WSW SJT 30 N FST
50 WSW PEQ 55 SE MMCS 40 SSW MMCS 100 SW MMCS 70 SE DUG 60 S OLS
95 WSW OLS 100 SE YUM 30 SSW NYL 30 SW BLH 20 SE TRM 30 ENE RNM
25 ESE RIV 35 SSW DAG 15 ENE DAG 45 SSW DRA 15 N DRA 45 NNE DRA
45 WSW SGU SGU 30 SE CDC 25 SW PGA 40 E GCN 35 NNW INW 25 E INW
35 NNW SOW 20 N SOW 15 WSW SJN.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW ELP LRU 15 SE DMN 40 SW DMN 50 ENE DUG 35 E DUG
35 SSW DUG 35 SSE OLS 40 SSW OLS 60 WSW OLS 80 WSW OLS 100 W OLS
90 S GBN 70 WSW TUS 40 NNW DMA 45 ESE IWA 60 WNW SAD 40 S SOW
25 SSE SOW 45 SE SJN 50 NW TCS 10 NNW SRR 25 E SRR ATS
20 SSW ATS 50 NW GDP 35 S ALM 30 NNE ELP 20 NNW ELP.


SOUTHWEST INTO THE SOUTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
LARGE SLIGHT TO MODERATE RISK AREAS WERE MAINTAINED ON THE LATEST
EXCESSIVE RAINFALL POTENTIAL OUTLOOK FROM THE SOUTHWEST INTO THE
SOUTHERN PLAINS.  WIDESPREAD HEAVY TO EXCESSIVE RAINFALL LIKELY
THIS PERIOD ASSOCIATED WITH THE CIRCULATION OF ODILE AND WELL TO
THE EAST OF THIS CIRCULATION IN THE MUCH ABOVE AVERAGE PW AXIS
THAT WILL STRETCH FROM SOUTHERN CA/SOUTHERN NV---EASTWARD INTO
AZ---NM AND INTO THE SOUTHERN PLAINS.  OBSERVED PW VALUES ACROSS
THESE AREAS ARE NEAR OR ABOVE THE 99 PERCENTILE FOR
SEPTEMBER---WITH NO SIGNIFICANT CHANGES EXPECTED DURING THIS
PERIOD TO THESE VALUES.  THERE IS A STRONG MODEL SIGNAL FOR HEAVY
TO EXCESSIVE RAINFALL AMOUNTS ACROSS SOUTHEASTERN AZ---SOUTHERN
NM---LEADING TO HIGH CONFIDENCE ACROSS THESE AREAS.  FARTHER TO
THE EAST FROM THESE AREAS--THERE IS MORE MODEL SPREAD WITH HOW
QUICKLY HEAVY PRECIPITATION BREAKS OUT INTO THE SOUTHERN PLAINS.
THE HI RES MODELS ARE MORE EMPHATIC ACROSS THIS AREA---BUT STILL
HAVE SOME SIGNIFICANT NORTH-SOUTH DIFFERENCES WITH THEIR
RESPECTIVE AXES.  CONFIDENCE IS LOWER HERE--BUT WITH THE ABOVE
MENTIONED HIGH PW AXIS AND MODEL FORECASTS OF UPPER DIFFLUENCE
MAXIMUM IN THIS HIGH PW AXIS---FAVOR THE HI RES IDEA OF SPREADING
HEAVY TO LOCALLY EXCESSIVE RAINFALL AMOUNTS EASTWARD QUICKER.
WHILE MODELS DO NOT DEPICT MUCH PRECIPITATION ON THE NORTHWESTERN
PORTION OF THE ANOMALOUS PW AXIS FROM SOUTHERN CA INTO SOUTHERN NV
AND NW AZ---SCATTERED CONVECTION LIKELY AGAIN ACROSS THESE
AREAS--WITH LOCALLY HEAVY TO EXCESSIVE RAINFALL AMOUNTS POSSIBLE.


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW BVX 20 E FYV 25 NE CNU 25 SSE FNB 15 W CDJ 10 E VIH
20 N ARG 20 SW BVX.


PORTIONS OF MO/AR
~~~~~~~~~~~~~~~~~
THUNDERSTORMS HAVE DEVELOPED OVER THE PAST FEW HOURS WITHIN A WARM
ADVECTION REGIME, FOCUSED JUST NORTHEAST OF A STATIONARY FRONT DUE
TO SOME CIN ALONG THE BOUNDARY.  INFLOW AT 850 HPA IS MODERATELY
BROAD AND ON THE ORDER OF 25-30 KTS ACROSS THE REGION.  MOST
UNSTABLE CAPE VALUES OF 1000-2000 J/KG LIE UPSTREAM ACROSS EASTERN
KS AS WELL AS SOUTHWEST MO.  PRECIPITABLE WATER VALUES ARE JUST
OVER 1.5" PER RECENT RAP GUIDANCE, WHICH SUPPORTS HOURLY RAIN
RATES UP TO 2".  THE FORECAST IS FOR THE BAND TO EXTEND FARTHER
SOUTHEAST WITH
TIME THIS MORNING, POSSIBLY INTO NORTHWESTERN AR, AS THE MAGNITUDE
OF THE 850 HPA INFLOW REMAINS CONSTANT WHILE SLOWLY SHIFTING
SOUTHWARD PER RECENT RAP GUIDANCE.  CAPE VALUES SHOULD BE
SUFFICIENT TO MAINTAIN
CONVECTION WELL INTO THE MORNING.  PROPAGATION TO THE SOUTHEAST
WITH TIME COULD CAUSE A PERIOD OF TRAINING CONVECTION OVER THE
NEXT SEVERAL HOURS DUE TO CELL BACKBUILDING.  OUR HYPOTHESIS IS
THAT MIXING CAUSED BY DAYTIME HEATING COULD DISRUPT THIS ACTIVITY
BY 16Z, BUT IT COULD PERSIST LONGER.  THE MESOSCALE GUIDANCE
ADVERTISES LOCAL AMOUNTS OF 2-4" IN THIS REGION, CLOSE TO THE
THREE HOUR FLASH FLOOD GUIDANCE VALUES, THOUGH THEIR PLACEMENT
SHOWS A BIT OF DISPERSION.  THIS AREA WAS ADDED AS A RESULT OF
MESOSCALE PRECIPITATION DISCUSSION #0378.


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SW HXD SVN 10 NW SAV 20 SE JYL 25 WNW NBC 30 SE OGB 40 E OGB
45 NNE CHS 40 WSW MYR 40 SSW MYR 30 E CHS 10 SW HXD.

COASTAL SOUTH CAROLINA
~~~~~~~~~~~~~~~~~~~~~~
A SLIGHT RISK WAS RE-INTRODUCED ACROSS COASTAL SOUTH CAROLINA FOR
POTENTIAL OF ANOTHER DAY OF SCATTERED CONVECTION.  A SURFACE
FRONTAL BOUNDARY WILL BE SINKING SOUTHEASTWARD THROUGH SOUTHERN
MID ATLANTIC AND INTO THE SOUTHEASTERN U.S. THIS PERIOD.  ANOTHER
DAY OF WIDELY SCATTERED CONVECTION POSSIBLE ACROSS THE
SOUTHEASTERN U.S. IN AN AXIS OF INCREASINGLY UNSTABLE CONDITIONS
WEDNESDAY AFTERNOON/EARLY EVENING.  PW VALUES HAVE LOWERED FROM
THE PREVIOUS DAYS---AS THE INITIAL FRONTAL BOUNDARY HAS PUSHED
SOUTHWARD--BUT REMAIN NEAR SEASONAL LEVELS IN THE 1.50-1.75"
RANGE.  WITH WELL DEFINED FRONTAL/PRE FRONTAL CONVERGENCE FORECAST
ACROSS THE COASTAL SOUTHEAST---ADDITIONAL LOCALLY HEAVY TO
ISOLATED EXCESSIVE RAINFALL AMOUNTS POSSIBLE FOR THE COASTAL
CAROLINAS WHERE HEAVY RAINS HAVE OCCURRED OVER THE PAST SEVERAL
DAYS.  ISOLATED 1-2"+ AMOUNTS POSSIBLE ACROSS COASTAL SECTIONS OF
SOUTH CAROLINA.


ROTH/ORAVEC
$$





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