Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 201321
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
921 AM EDT SAT AUG 20 2016

...VALID 1321Z SAT AUG 20 2016 - 12Z SUN AUG 21 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
130 ESE MMCU 30 ENE 6R6 30 NW E29 25 SE BPG 45 N ABI RKR
15 W FLP 25 NNW CGI BAK 10 NW AOH 20 SW CLE BVI 20 SSE AGC
20 NW HSP 35 WSW TNB 10 NW GVL 25 NW BHM 35 SE GLH 45 W IER
70 S MMMY.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NW CYSB 55 NNE CYZE GOV 35 ESE MTW 20 ENE CLI 25 NNW IMT
35 NNE CYXZ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 NNW MMMV 20 E E29 25 E SJT 10 S ABI RUE 20 SE SRC
15 ESE PBF GGG 35 SE BAZ 30 NNW MMAN.


...SPECIAL 13Z UPDATE...

IN TEXAS AND THE ARKLATEX...INCLUDING SOUTHEAST
OKLAHOMA...SYNOPTIC ASCENT ASSOCIATED WITH A NORTHERN STREAM
DIGGING TROUGH AND SLOW MOVING CIRCULATION ACROSS SOUTH TEXAS WILL
TAKE ADVANTAGE OF BROAD UNSTABLE INFLOW WITH ANOMALOUS
PRECIPITABLE WATER VALUES TO PRODUCE A RISK OF FLASH FLOODING.
MUCH OF THIS AREA HAD ONGOING CONVECTION THIS MORNING. SEE
MESOSCALE DISCUSSIONS 582 AND 583 FOR DETAILS. THE RAP AND GFS
SHOW ENOUGH OF A SYNOPTIC ASCENT SIGNAL...AND THE SSEO
MEAN...ALONG WITH PARTICULARLY THE WRF-ARW...DEPICT ENOUGH
PRECIPITATION FOR AN EXPANSION OF SLIGHT RISK INTO MORE OF CENTRAL
AND NORTHEAST TEXAS...CONTINUING INTO PARTS OF OK/AR...AND JUST
THE NORTHWEST CORNER OF LOUISIANA. PREVIOUS DISCUSSION FOLLOWS...


...TEXAS / SOUTHERN PLAINS INTO THE LOWER MS VALLEY...

THE WESTERN PORTION OF THE FRONT ASSOCIATED WITH THE AMPLIFYING
MID U.S. TROF CURRENTLY PRESSING SOUTHWARD INTO THE SOUTHERN
PLAINS IS EXPECTED TO SLOW SATURDAY AS IT PRESSES FARTHER SOUTH
INTO THE SOUTHERN PLAINS AND LOWER MS VALLEY.  THIS WILL ALLOW THE
AXIS OF ABOVE AVERAGE PW VALUES TO PERSIST LONGER IN THE VICINITY
OF THE FRONT ACROSS THE SOUTHERN PLAINS INTO THE LOWER MS
VALLEY--SUPPORTING POTENTIAL FOR LOCALLY HEAVY PRECIP TOTALS
ACROSS NORTHEAST TX INTO THE LOWER MS VALLEY.

TO THE SOUTH OF THE FRONT MOVING INTO THE SOUTHERN PLAINS---THERE
IS A STRONG MODEL SIGNAL FOR HEAVIER RAINFALL AMOUNTS IN THE
VICINITY OF 100W FROM THE U.S./MEXICAN BORDER---NORTHEASTWARD
ACROSS THE TX HILL COUNTRY IN THE VICINITY OF SAN
ANTONIO..AUSTIN---WACO. THIS IS IN ASSOCIATION WITH VORTICITY
MAXIMA EXPECTED TO LIFT NORTHEASTWARD FROM NORTHEAST MEXICO INTO
CENTRAL TO NORTHEAST TX. THERE ARE A VARIETY OF MODEL SOLUTIONS
WITH RESPECT TO THE DETAILS OF THESE VORTICITY MAXIMA---BUT
GENERAL AGREEMENT ON POTENTIAL FOR HEAVY TO ISOLATED EXCESSIVE
RAINFALL AMOUNTS WITHIN THIS AXIS.


...CENTRAL APPALACHIANS/UPPER OH VALLEY---TN VALLEY...

THE FRONTAL BOUNDARY FROM THE AMPLIFYING TROF OVER THE UPPER MS
VALLEY/UPPER LAKES IS EXPECTED TO BE VERY PROGRESSIVE TO THE EAST
AND SOUTHEAST THROUGH THE LOWER LAKES---OH VALLEY AND TN VALLEY.
WHILE PW VALUES WILL BE ABOVE AVERAGE IN A NARROW BAND ALONG AND
AHEAD OF THE FRONT---2 TO 2.5 STANDARD DEVIATIONS ABOVE THE
MEAN---THE PROGRESSIVE NATURE OF THE BOUNDARY WILL LIMIT POTENTIAL
FOR VERY HEAVY TOTALS. STILL---WELL DEFINED FRONTAL CONVERGENCE IN
THIS HI PW AXIS WILL SUPPORT LOCALLY HEAVY PRECIP TOTALS ALONG AND
AHEAD OF THIS FRONT. A MARGINAL RISK AREA WAS DEPICTED FROM THE
CENTRAL APPALACHIANS/UPPER OH VALLEY REGION INTO THE TN VALLEY
WHERE THERE ARE POCKETS OF RELATIVELY LOWER FFG VALUES IN 1-1.5"
RANGE IN AN HOUR.


...UPPER LAKES...

THE DEEPENING CYCLONE ROTATING THROUGH THE UPPER MS VALLEY/UPPER
LAKES REGION WILL SUPPORT AN ENHANCING COMMA HEAD/DEFORMATION
PRECIPITATION AREA FROM PORTIONS OF THE UPPER MS
VALLEY---NORTHEASTWARD INTO THE UPPER LAKES.  WITH FAIRLY GOOD
MASS FIELD EVOLUTION AMONG THE LATEST MODELS---THERE IS SIMILAR
QPF DISTRIBUTIONS.  HEAVY RAINS LIKELY IN THIS COMMA HEAD
REGION---WITH AREAL AVERAGE 1-2"+ TOTALS FROM NORTHERN WI INTO
EASTERN PORTIONS OF THE UPPER PENINSULA OF MI AND NORTHERN LOWER
PENINSULA--- WITH ISOLATED TOTALS GREATER THAN 3"
POSSIBLE---ESPECIALLY OVER THE CENTRAL U.P. AND FAR NORTHERN WI
WHERE LAKE ENHANCEMENT TO THE PRECIPITATION IS POSSIBLE FROM
STRONG NORTHERLY TO NORTHWESTERLY FLOW OFF OF LAKE SUPERIOR.

BURKE/ORAVEC
$$





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