Quantitative Precipitation Forecast
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000
FOUS30 KWBC 260337
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1136 PM EDT THU JUN 25 2015

...VALID 0336Z FRI JUN 26 2015 - 12Z FRI JUN 26 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSW HYS 45 N RSL 15 S AFK 20 WNW IJX 15 N FFT 10 NW BKW MKJ
25 W TNB 15 E TYS 15 SSE PAH 40 N SGF 30 E PTT 35 SSW HYS.


03Z UPDATE...

MADE SOME MODIFICATIONS TO THE EXCESSIVE RAINFALL OUTLOOK THROUGH
12Z 06/26 BASED ON (MOSTLY) CURRENT SATELLITE/RADAR/OBS
TRENDS...WITH THE MAJORITY OF THE GUIDANCE (INCLUDING HIGH-RES
CONVECTIVE-ALLOWING MODELS) HAVING A POOR HANDLE ON THE CURRENT
EVOLUTION ACROSS THE CENTRAL PLAINS ESE INTO THE MID MS VLY AND
LOWER OH VLY.

ACROSS THE MID ATLANTIC REGION...LAST AREA OF UNTAPPED DEEP-LAYER
INSTBY (MIXED-LAYER CAPES 1000-2000 J/KG) IS NOW CONFINED ACROSS
SOUTHEASTERN VA AND ACROSS THE LOWER-MID DELMARVA. THIS ALONG WITH
THE UPPER LEVEL FORCING ASSOCIATED WITH THE LOW AMPLITUDE
SHORTWAVE (MCV)...STRENGTHENED LOW-LEVEL MOISTURE FLUX CONVERGENCE
ALONG AND NORTH OF THE SURFACE BOUNDARY...AND PWATS SPIKING
BETWEEN 1.75 AND 2.00 INCHES PER THE LATEST GPS DATA AND BLENDED
TPW LOOPS...WILL CONTINUE TO ALLOW FOR LOCALIZED HOURLY RAINFALL
RATES OF 2-2.5+ INCHES. THIS WILL LEAD TO ISOLATED SHORT-TERM
RUNOFF ISSUES...ESPECIALLY ACROSS POOR DRAINAGE AREAS IN HAMPTON
ROADS WHERE THE FFG IS LOWER (1-1.5 INCHES IN 1 HOUR).

FROM KS/MO ESE THROUGH SOUTHERN IL/IN AND INTO MUCH OF
KY...NORTHEAST TN...AND INTO THE WESTERN SLOPES OF THE
SOUTHERN-CENTRAL APPALACHIANS...SHIFTED THE BROAD SLIGHT RISK
REGION A BIT FARTHER TO THE SOUTH TO ACCOUNT FOR THE SOUTHWARD
TRENDS OF THE LOW LEVEL FRONTAL PROGRESSION (AIDED BY CONVECTIVE
OUTFLOWS THIS EVENING)...AND THUS ALSO THE SHIFT SOUTHWARD OF THE
MORE FAVORABLE DEEP-LAYER INSTBY AND MOISTURE FLUX INTO AND JUST
NORTH OF THE SURFACE BOUNDARY ALONG THE SURFACE BOUNDARY.

ACROSS THE CENTRAL HIGH PLAINS...SHORTWAVE TROUGH/HEIGHT FALLS
DROPPING SOUTHEAST INTO THE CENTRAL PLAINS AROUND 06Z WILL LEAD TO
A DISSIPATION OF FAVORABLE UPPER LEVEL FORCING ACROSS THE CO FRONT
RANGE...SOUTHWEST NE...AND WESTERN KS. STRENGTHENED UPSLOPE
EASTERLY LOW LEVEL FLOW AND ANOMALOUS MOISTURE AVAILABILITY (PW)
UNTIL THEN HOWEVER WILL MAINTAIN THE RISK OF ISOLATED RUNOFF
ISSUES WITHIN THE HEAVIER (ALBEIT PROGRESSIVE/DOWNWIND
PROPAGATING) CONVECTIVE CLUSTERS.

HURLEY


01Z UPDATE...

A COUPLE OF ADJUSTMENTS WERE MADE TO PREVIOUS OUTLOOK AREAS TO
REMOVE AREAS WHERE THREAT HAS DIMINISHED.

ACROSS THE CNTL HIGH PLAINS....FEEL MAIN EXCESSIVE THREAT SHOULD
CONTINUE TO SHIFT SWD ACRS SE WY/WRN NEB INTO NE CO DURING THE
EARLY OVERNIGHT AS A WELL DEFINED BAND OF CONVECTION ACRS WRN NEB
DIVES SEWD TOWARD AXIS OF 3000 J/KG CAPE OVER NE CO DURING THE
EARLY OVERNIGHT PD.  SOME LOCAL 1 TO 1.5 INCH RAINFALL AMOUNTS
WILL BE PSBL IN SOME OF THE MORE INTENSE CELLS WHICH COULD RESULT
IN RUNOFF PROBLEMS IN SOME AREAS WITH LOWER FFG VALUES.

FROM THE MID MS VALLEY INTO THE SRN OH VALLEY...REDUCED SLIGHT
RISK AREAS ACRS PARTS OF SRN OH INTO WV AS BEST INSTABILITY AND
LOW LEVEL MSTR CONVERGENCE HAS LINED UP ALONG WELL DEFINED FRONTAL
BNDRY FROM MO EWD INTO NRN KY.  GREATEST SHORT TERM THREAT IS
EXPECTED FROM PARTS OF NRN/CNTL MO INTO SRN IN.  PLEASE SEE MPD
#271 IN EFFECT UNTIL 0548Z FOR MORE DETAIL.

ACRS THE SRN MID ATLC REGION...FEEL THREAT OF EXCESSIVE RAINS WILL
CONTINUE THROUGH AT LEAST THE EARLY OVERNIGHT PD AS TSTMS BECOME A
BIT MORE ORGANIZED AHEAD OF DVLPG SFC WAVE NEAR CHO AS OF 00Z.
STG LOW LEVEL MSTR ADVECTION WAS NOTED ON OVER THE LAST SEVERAL
HOURS WITH GOES SOUNDER IMAGERY SHOWING PWS INCREASING TO OVER
1.75 INCHES OVER PARTS OF ERN VA INTO SRN MD...WITH SB CAPES
BETWEEN 1000 TO 2500 J/KG.   HIGH RAINFALL RATES WITH SHORT TERM
TOTAL IN EXCESS OF 3 INCHES WILL BE PSBL.   FOR MORE INFO...PLEASE
SEE MPD#270 IN EFFECT UNTIL 0522Z.
SULLIVAN    PREVIOUS DISCUSSION FOLLOWS....


...MID MISSISSIPPI VALLEY EAST TO THE CENTRAL APPALACHIANS...

A PRONOUNCED SHORTWAVE TROUGH OVER THE MIDWEST WILL SLIDE EASTWARD
TODAY WHILE SLOWLY AMPLIFYING. DEEPER MOISTURE WHICH HAD ADVANCED
INTO EASTERN MO AND IL WILL CONTINUE TO SPREAD EAST TOWARD THE
MOUNTAINS IN WV THIS AFTERNOON. A SECOND SHORTWAVE WILL APPROACH
MISSOURI DURING THE NEXT LOW LEVEL JET CYCLE THIS EVENING. ALONG A
ZONE FROM THE CENTRAL PLAINS TO THE APPALACHIANS THE PRECIPITABLE
WATER VALUES AND PRESENCE OF DEEP LAYER FORCING DURING A
SUMMERTIME DIURNAL CYCLE IS CAUSE ENOUGH FOR CONCERN ABOUT HEAVY
RAINFALL. MODEL PRECIPITATION IS NOT ESPECIALLY FOCUSED...BUT
24-HOUR MAXIMA ARE EXPECTED DOWNWIND OF THE GREATEST MOISTURE
TRANSPORT OVER SOUTHERN IN / SOUTHWEST OH / NORTHERN KY...AND AT
THE EDGE OF THE GREAT PLAINS CAP OVER NORTHERN MO.

EASTWARD AND ESPECIALLY NORTHWARD PROGRESSION OF INSTABILITY MAY
BE TEMPERED BY ONGOING EARLY MORNING CONVECTION. WPC MAINTAINED A
BROAD SLIGHT RISK OF EXCESSIVE RAINFALL ALONG A ZONE THAT IS
BETTER CHARACTERIZED BY DEEP LAYER MOISTURE STRETCHING WEST TO
EAST...RATHER THAN ANY SURFACE BOUNDARY...ALTHOUGH LESS SEPARATION
BETWEEN THE SURFACE WARM FRONT TO THE SOUTH AND THE INSTABILITY
AXIS TO THE NORTH WILL BE SEEN OVER THE MID MISSISSIPPI VALLEY.
BASED ON VARIOUS MODEL CAPE FORECASTS AND PLACEMENT OF 700 MB
FORCING AT 21-00Z...WE ATTEMPTED TO LIMIT THE NORTHWARD AND
EASTWARD EXTENT OF THE RISK AREA...ALSO PROVIDING SOME SEPARATION
BETWEEN THIS EVENT AND A SECOND RISK AREA OVER THE MID ATLANTIC.

WPC GENERALLY FOLLOWED THE WRF-ARW AND ITS PARALLEL VERSION IN
TERMS OF THE TIMING/TRACK OF THE EARLY MORNING MCS IN THE OHIO
VALLEY. ALSO LEANED TOWARD THE WRF-ARW WITH THE NEXT MCS
OVERNIGHT...WITH THE MAX QPF CENTERED ACROSS NORTHERN-CENTRAL MO
(CONTINUING A SW-S TREND FROM THE PREVIOUS NIGHT). ALL OF THIS
ACTIVITY WILL BE OCCURRING SOUTH OF AREAS THAT RECEIVED HEAVY
ANTECEDENT RAINFALL THE PAST FEW DAYS. STILL...LOCALLY HEAVY RAIN
RATES COULD LEAD TO FLASH FLOODING. IN MISSOURI...MESOSCALE
GUIDANCE SHOWS ISOLATED TOTALS ABOVE 4 INCHES. ELSEWHERE QUICK
ACCUMULATIONS OF 1 TO 3 INCHES ARE POSSIBLE.


...MID ATLANTIC...

WITHIN MODERATE WESTERLY FLOW ALOFT...SUBSTANTIAL HEIGHT FALLS
WILL OVERSPREAD THE EASTERN OHIO VALLEY BY AFTERNOON AND ENTER THE
MID ATLANTIC OVERNIGHT. IN RESPONSE...LOW LEVEL MOISTURE AND
GENERALLY DEEPER/STRONGER MOISTURE/INSTABILITY PROFILES WILL
MIGRATE NORTHWARD ALONG AND AHEAD OF A WARM FRONT ENTERING CENTRAL
AND SOUTHERN VIRGINIA THIS AFTERNOON. SEVERAL HIGH RESOLUTION
MODELS GENERATE A CONCENTRATED AREA OF DEEP CONVECTION THIS
AFTERNOON/EVENING NEAR THE WARM FRONT IN VIRGINIA. AS NOTED IN THE
STORM PREDICTION CENTER OUTLOOK...VEERING PROFILES COULD FAVOR
SUPERCELL CHARACTER WHICH COULD SLOW CELL MOTIONS DOWN TO AROUND
10 KNOTS. THIS WOULD INCREASE THE ODDS OF LOCALLY PERSISTENT HEAVY
RAIN RATES...WITH PRECIPITABLE WATER RISING TO AROUND 1.6 INCHES.
THE 00Z WRF ARW...NSSL WRF...AND NAM CONEST ALL INDICATE
PARTICULARLY HEAVY RAINS IN CENTRAL VA THROUGH 12Z FRIDAY. FARTHER
NORTH...CLOUD BASES WILL BE HIGHER AND INSTABILITY LESS...BUT
CONTINUED MOISTURE TRANSPORT AND ARRIVAL OF THE UPSTREAM TROUGH
MAY SUSTAIN SCATTERED CONVECTION WELL AFTER DARK...WITH LOCALLY
HEAVY DOWNPOURS OCCURRING IN AREAS OF LOWER FLASH FLOOD GUIDANCE
OVER THE DC METRO AND NORTHERN MARYLAND.


...HIGH PLAINS OF WY/SD/NE/CO...

POCKETS OF HEAVY RAIN WERE ALREADY OBSERVED EARLY THURSDAY MORNING
WITHIN A WARM ADVECTION AND MID LEVEL FRONTOGENESIS REGION AHEAD
OF A WELL DEFINED SHORTWAVE TROUGH. BROADLY CONVERGENT SURFACE
FLOW...AND SOME UPSLOPE COMPONENT WILL PERSIST TODAY...WITH
UPSLOPE BEST DEFINED INTO THE BLACK HILLS AND ALSO NORTHEAST
COLORADO. WITH THE UPPER TROUGH PASSING OVERHEAD DURING DIURNAL
HEATING...SCATTERED THUNDERSTORMS ARE LIKELY. THE PRECIPITATION
SIGNAL IN THE CONVECTION RESOLVING MODELS IS NOT VERY
FOCUSED...BUT LOCALLY HEAVY RAIN IS INDICATED THROUGHOUT THE
SLIGHT RISK AREA FROM WY/SD INTO NE/CO. THE ENVIRONMENT TODAY
FEATURES ANOMALOUS MOISTURE (PWS 2-2.5 STANDARD DEVIATIONS ABOVE
NORMAL) AND FAVORABLE DEEP LAYER INSTABILITY (MIXED-LAYER CAPES
~1000 J/KG EARLY INCREASING TO 1500-2000 J/KG LATER TODAY). A
SMALL CLUSTER OF STORMS IN A SIMILAR ENVIRONMENT PRODUCED FLASH
FLOOD IMPACTS EAST OF DENVER YESTERDAY...AND FLASH FLOOD GUIDANCE
REMAINS RATHER LOW OVER THIS REGION AFTER A WET SPRING.

HURLEY/BURKE
$$




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