Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 290146
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
945 PM EDT THU AUG 28 2014

...VALID 03Z FRI AUG 29 2014 - 00Z SAT AUG 30 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW PDC 30 SE CNC 15 N STJ 15 WNW FNB TQE SPW 15 E STP PBH
25 S IMT 15 NNW MTW 20 SW PDC.


01Z UPDATE...MADE FEW CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL
OUTLOOK...BASED ON THE LATEST RADAR TRENDS. THE MAIN AREA OF
CONCERN CONTINUES TO BE ACROSS PORTIONS OF THE CENTRAL MS VLY (FAR
EASTERN NE...MUCH OF IA...SOUTHEASTERN MN...AND INTO CENTRAL
WI)...WHERE THE COMBINATION OF LOWER 1-3 HOURLY FLASH FLOOD
GUIDANCE AND IMPRESSIVE PRE-TROUGH THERMODYNAMICS ARE IN PLAY.
CURRENT POOLING OF 1.75+ INCH PWATS HAS LIFTED INTO IA AND
SOUTHEASTERN MN... WITH THE 00Z RAOBS INDICATING 1.79" AT MPX AND
1.93" AT DVN. 30-40 KT SOUTHWESTERLY LOW LEVEL INFLOW WILL BECOME
PARALLEL TO THE 850-300 MB FLOW...WHILE REACHING (OR EXCEEDING)
THE MAGNITUDE OF THE MEAN FLOW OVERNIGHT ACROSS THE OUTLOOK AREA.
THE LATEST RAP AND NAM GUIDANCE CONTINUES TO SHOW THIS...AND AS A
RESULT...EXPECT WEAKENING CORFIDI/MBE VECTORS...WITH UPWIND
PROPAGATION AND BACK-BUILDING/TRAINING OF CELLS BECOMING MORE
LIKELY. DEEP LAYER INSTBY SHOULD REMAIN SUFFICIENT FOR LOCALLY
HEAVY (POTENTIALLY EXCESSIVE) RAINFALL RATES
OVERNIGHT...PARTICULARLY ACROSS IA WHERE MUCAPES WILL REMAIN
BETWEEN 1000-2000 J/KG.

HURLEY


PREVIOUS DISCUSSION BELOW...


...PORTIONS OF THE LOWER MO VALLEY INTO THE UPPER MS VALLEY...

OVERALL---THERE WERE NOT A LOT OF CHANGES MADE TO THE PREVIOUS
EXCESSIVE RAINFALL POTENTIAL AREA ACROSS THIS REGION---ALTHOUGH
THE LATEST AREA IS ASSOCIATED WITH ADDITIONAL ORGANIZED HEAVY RAIN
POTENTIAL TONIGHT INTO FRIDAY.  NO MAJOR MODEL DIFFERENCES WITH
THE EVOLUTION OF THE UPPER TROF INITIALLY STRETCHING THROUGH THE
NORTHERN TO CENTRAL HIGH PLAINS AS IT PUSHES EASTWARD THIS PERIOD.
 AN AXIS OF HIGH PW VALUES 1.75"+ WILL ACCOMPANY THIS TROF---WITH
THE MOST ANOMALOUS VALUES CONCENTRATED AHEAD OF THE NORTHERN
PORTION OF THE UPPER TROF FROM THE UPPER MS VALLEY INTO THE UPPER
LAKES.   THIS AREA WILL BE ALONG AND NORTH OF THE WARM FRONTAL
BOUNDARY FORECAST TO BE PUSHING NORTHEASTWARD THROUGH THE UPPER MS
VALLEY.  WHILE THE EARLIER ORGANIZED CONVECTION TO THE NORTHEAST
OF THIS FRONT HAS WEAKENED THIS AFTERNOON---ADDITIONAL ORGANIZED
ACTIVITY AGAIN LIKELY AFTER 0000 UTC FRI AS THE LOW LEVEL SOUTH
SOUTHWESTERLY INFLOW INTO THIS FRONT STRENGTHENS.  THIS WILL
SUPPORT AN AXIS OF POTENTIALLY HEAVY TO EXCESSIVE RAINFALL
AMOUNTS--WITH AGAIN MODELS SHOWING DIFFERENCES WITH THE LATITUDE
OF THE MAX QPF AXIS.  OUR OVERALL HIGHER CONFIDENCE IN THE HI RES
RUNS OF THE ARW AND NMM HAVE LEAD US TO FAVOR THEIR AXES---WITH
THESE MODELS ON THE SOUTHERN END OF THE GUIDANCE ENVELOP.  A
PERIOD OF TRAINING OF CELLS POSSIBLE ALONG AND NORTH OF THE WARM
FRONT FROM IN THE VICINITY OF NORTHERN IA---SOUTHEAST MN INTO
CENTRAL WI AND THE L.P. OF MI IN THE 0000-1200 UTC FRI AUG 29TH
TIME FRAME.  IN AREAS OF ISOLATED TRAINING---SHORT TERM
PRECIPITATION TOTALS OF 2-4"+ POSSIBLE.

...WESTERN GULF COAST...

CONCERNS CONTINUE FOR LOCALLY VERY HEAVY TO ISOLATED EXCESSIVE
PRECIPITATION TOTALS ALONG PORTIONS OF THE TX GULF COAST.  THERE
IS NOT MUCH MOVEMENT EXPECTED TO THE WEAK SURFACE LOW OVER THE
WESTERN GULF OF MEXICO THIS PERIOD.  ONSHORE SOUTHEASTERLY FLOW IN
AN AXIS OF ABOVE AVERAGE PW VALUES WILL SUPPORT POTENTIAL FOR
ADDITIONAL PRECIPITATION AFFECTING COASTAL SECTIONS OF TX.  AT THE
MOMENT CONVECTION IS CONCENTRATING PERIODICALLY ALONG AN INVERTED
SURFACE TROF EXTENDING NORTH FROM THIS LOW OFF THE S TX COAST.
LATEST MODEL GUIDANCE IS SHOWING THIS TROF WEAKENING THIS
PERIOD---BUT THERE MAY LIKELY REMAIN A CONVERGENCE ZONE BETWEEN
THE SOUTHEASTERLY FLOW OFF THE WESTERN GULF AND AREAS INLAND OVER
COASTAL TX.  SUBSEQUENTLY---THERE MAY BE HEAVY RAIN BANDS
AFFECTING COASTAL TX---ALTHOUGH CONFIDENCE REMAINS LOW WITH
RESPECT TO WHERE THE WILL BE AND WHEN THEY WILL PERIODICALLY
ENHANCE.  IN AREAS WHERE CONVECTION DOES ENHANCE---SHORT TERM
PRECIPITATION TOTALS OF 1-2"+ POSSIBLE.

ORAVEC
$$





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