Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 110057
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 PM EDT TUE OCT 10 2017

...VALID 01Z WED OCT 11 2017 - 12Z WED OCT 11 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SW MMRX EBG 30 WSW KOPM 35 E PIL 50 SE MMMA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE IKK 15 ENE GEZ 25 SE SDF 25 WNW HOP 30 E POF 20 NW SUS
20 NW PIA 20 ESE IKK.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE AVL 1A5 35 W RHP 30 NE CHA 25 SE CSV OQT 6V3 15 S HSP
25 NE LYH 30 SW FVX 10 NW TDF RUQ 20 ESE AVL.


...MIDWEST/OH VALLEY...

STRONG SYNOPTIC SCALE LIFT AHEAD OF A SHORT WAVE OVER MO EARLY
THIS EVENING IS EXPECTED TO TAP DEEP MOISTURE AND MARGINAL
INSTABILITY TO SUPPORT AT LEAST SCATTERED CONVECTION AHEAD OF A
COLD FRONT ACROSS THE MIDWEST AND OH VALLEY DURING THE OVERNIGHT
HOURS. SOUTH AND EAST OF THE FRONT BOUNDARY...00Z SOUNDINGS SHOWED
MARGINAL INSTABILITY IN PLACE AND A FAIRLY UNIFORM FLOW IN THE
COLUMN. THIS COULD SUPPORT LOCALIZED TRAINING AHEAD OF THE FRONT
ACROSS IL INTO SOUTHERN IN AS THE CELLS ON THE LINE MOVE SOUTHWEST
TO NORTHEAST...WHILE THE LINE ITSELF MOVES EAST.

FURTHER NORTH INTO THE COOLER AIR NORTH OF THE FRONTAL
BOUNDARY...ELEVATED INSTABILITY (AS SHOWN ON THE 11/00Z KDVN
SOUNDING) COULD SUPPORT AN AREA OF LONGER DURATION MODERATE TO
HEAVY RAINFALL ACROSS PORTIONS OF NORTHERN IL (INCLUDING THE
CHICAGO METRO AREA)/SOUTHERN WI INTO NORTHERN IN COULD POSE A
LIMITED FLASH FLOOD THREAT. HIGH RESOLUTION GUIDANCE (INCLUDING
THE MOIST RECENT HRRR) SUGGEST THAT NORTHERN IN WILL BE THE TARGET
FOR THE HIGHEST QPF...MAINLY AFTER 11/03Z.


...FAR SOUTH TX...

THE COLD FRONT HAS CLEARED THE FAR SOUTH TX COAST...BUT THE COLUMN
REMAINS MOIST IN BEHIND IT (AS SHOWN ON THE 11/00Z KBRO SOUNDING).
AS THE FRONT SLOWS ACROSS THE WESTERN GULF OF MEXICO...THE DEEP
EASTERLY FLOW CONTINUES TO SUPPLY MOISTURE (WITH THE 00Z KBRO
SOUNDING SHOWING A 2.33 PRECIPITABLE WATER VALUE...WHICH IS ABOUT
TWO STANDARD DEVIATIONS ABOVE THE MEAN) IS EXPECTED TO RIDE UP AND
OVER THE BOUNDARY...SENDING DEEP MOISTURE AND MARGINAL INSTABILITY
ACROSS FAR SOUTH TX THROUGH THE EARLY MORNING HOURS. THE LATEST
RAP SOLUTION SUGGESTS THAT INSTABILITY COULD END UP BEING THE
LIMITING FACTOR FOR A MORE ORGANIZED THREAT...BUT GIVEN THE DEEP
MOISTURE IN PLACE...AS WELL AS A SOURCE OF LIFT...THE MARGINAL
RISK AREA HAS BEEN LEFT IN PLACE.


...SOUTHERN APPALACHIANS...

A FRONTAL BOUNDARY EXTENDING FROM THE SOUTHERN DELMARVA INTO
SOUTHEAST KY WILL BECOME THE FOCUS FOR DEEP MOISTURE AND MARGINAL
INSTABILITY FOR CONVECTION INTO THE OVERNIGHT HOURS. ALONG AND
SOUTH OF THE FRONT...PRECIPITABLE WATER VALUES NEAR 2.00 INCHES
(WHICH IS BETWEEN TWO AND THREE STANDARD DEVIATIONS ABOVE THE
MEAN) AND MARGINAL INSTABILITY (THOUGH THE 11/00Z KRNK SOUNDING
INDICATED SBCAPE VALUES APPROACHING 2000 J/KG) WILL SUPPORT
CONVECTION THROUGH THE EARLY MORNING HOURS STRETCHING ALONG THE
FRONT.

DIFLUENT FLOW IN THE 500-300 MB LAYER COULD AID IN ORGANIZATION OF
THE CONVECTION...AND THE FAIRLY WEAK MID LEVEL FLOW COULD SUPPORT
SLOW MOVING CELLS AND/OR LOCALIZED TRAINING.
ULTIMATELY...INSTABILITY COULD END UP BEING THE LIMITING FACTOR
FOR A MORE ORGANIZED THREAT (AS DOES FAIRLY HIGH FLASH FLOOD
GUIDANCE...DUE TO DRY CONDITIONS IN PLACE). THE MOST RECENT HRRR
SHOWED THE POTENTIAL FOR LOCAL 3.00+ INCH RAINFALL AMOUNTS IN
SOUTHEAST VA). HOWEVER...CONVECTION IN A HIGH MOISTURE CONTENT
AIRMASS WITH THE POTENTIAL FOR TRAINING NECESSITATED EXTENDING THE
MARGINAL RISK ALONG THE FRONT FROM SOUTHEAST VA INTO PORTIONS OF
EASTERN KY FOR THE OVERNIGHT.


BURKE/ORAVEC/HAYES
$$





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