Quantitative Precipitation Forecast
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FOUS30 KWBC 270044
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
844 PM EDT FRI JUN 26 2015

...VALID 01Z SAT JUN 27 2015 - 12Z SAT JUN 27 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
TDZ 15 WSW HZY DUJ 25 S UNV 10 N MRB OKV 25 W CJR 15 E PTB
20 SSE EDE NKT 15 S NCA 15 S DPL 15 ESE RDU 20 S ROA 40 N LNP
20 SW JKL EKQ 35 SW BNA 10 SSE OLV 10 SSW JBR 15 N CGI 20 SE MVN
10 W 1H2 25 WSW TAZ 20 ESE PPQ 15 SSW UIN 15 WSW MQB 20 ESE PNT
TDZ.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNE HUF 20 S CMI 10 NW CMI 20 WNW LAF 20 ENE OKK 15 ENE FDY
25 NNE MFD 10 WSW CAK 25 WSW HLG 15 S PKB 30 WSW HTS 35 SW LEX
15 N BWG 20 E OWB 30 ESE HNB 20 WSW CVG 20 WNW CVG 15 SW IND
10 NNE HUF.


DAY 1

01Z UPDATE...
ACRS THE OH VALLEY...NARROWED MDT RISK AREA TO WARM CONVEYOR BELT
BAND NORTH OF WARM FRONT AHEAD OF LOW PRES SYSTEM MOVING SLOWLY
ENEWD FROM NEAR THE IND/OH BORDER REGION AS OF 00Z.  EXPECT THIS
BAND TO BECOME A BIT BETTER DEFINED DURING THE OVERNIGHT AS LOW
PRES SLOWLY INTENSIFIES IN RESPONSE TO CONTINUED HEIGHT
FALLS/COOLING ALOFT.  EXPANDING SLIGHT RISK A BIT EWD IN THE WARM
SECTOR TO THE SOUTH TO ACCOUNT FOR CONVECTION CONTINUING TO EXPAND
EWD WITH TRAILING COLD FRONT.  WELL DEFINED PLUME OF GREATER THAN
2 INCH PWS ALONG STRENGTHENING LOW LEVEL WSWLY JET SHOULD CONTINUE
TO SUPPORT BANDS OF INTENSE RAIN RATES OVERNIGHT ACRS PARTS OF THE
OH/TN VALLEYS TOWARD THE CNTL APLCNS AS CONVECTIVE LINE SEGMENTS
PROGRESS EWD.

...AR SWWD INTO TX...
THERE IS SOME CONCERN FOR ISOLD EXCESSIVE RAINFALL THREAT ALONG
AND SOUTH OF TRAILING COLD FRONT FROM AR SWWD INTO TX. ATMOSPHERE
AHEAD OF THE FRONT IS QUITE UNSTABLE WITH SB CAPES IN THE 1000 TO
3000 J/KG RANGE EARLY THIS EVENING.  00Z SOUNDINGS SHOW LITTLE IF
ANY CAP AHEAD OF THE FRONT AND WITH PWS APCHG 2 INCHES ALONG WITH
MODEST LOW LEVEL CONVERGE INTO THE BNDARY AND DIFFLUENT FLOW
ALOFT...CAN NOT RULE OUT LOCALLY HEAVY RAIN RATES FROM ANY
ORGANIZED STORMS THAT DVLP THIS EVENING INTO THE OVERNIGHT.  WHILE
SOME OF THE HIGH RES GUIDANCE SUPPORT POTNL FOR LOCAL RAINFALL
AMOUNTS IN EXCESS OF 3 INCHES...IT IS NOT UNANIMOUS WITH THE WRF
ARW CONSIDERABLY DRIER THAN BOTH THE NSSL WRF...WRF NMM AND NAM
CONEST...SO FOR THIS REASON DID NOT HIGHLIGHT A SLIGHT RISK AREA
AT THIS TIME.

SULLIVAN   PREVIOUS DISCUSSION FOLLOWS...

...MID MISSISSIPPI VALLY EAST THROUGH THE OHIO VALLEY AND INTO THE
CENTRAL/NORTHERN APPALACHIANS...

A MODERATE RISK OF EXCESSIVE RAINFALL IS FORECAST WHERE DEEP
SYNOPTIC SCALE ASCENT OVERLAPS WITH THE NORTHERN REACHES OF AN
INSTABILITY AXIS...ORIENTED WEST TO EAST. VERY LOW FLASH FLOOD
GUIDANCE VALUES OWING TO RECENT WET WEATHER...WAS ALSO A FACTOR IN
OUTLINING THE MODERATE RISK AREA...WHICH STRETCHES ACROSS CENTRAL
IL TO SOUTHERN IN AND SW OH...CATCHING JUST A SMALL PART OF KY.

STEEP HEIGHT FALLS WILL OVERSPREAD THE MID MS VLY AND OH/TN VLYS
DURING THE DAY ONE PERIOD...AS THE LONGWAVE RIDGE BUILDS IN THE
WESTERN CONUS WHILE AN UPPER LEVEL JET STREAK AND ASSOCIATED
SHORTWAVE OVER THE CENTRAL PLAINS EARLY THIS MORNING HELPS TO
CARVE OUT A LONGWAVE TROUGH ALONG AND EAST OF THE MS RIVER VALLEY.

THE SIGNAL REMAINS IN PLACE FOR A SYNOPTICALLY-DRIVEN HEAVY
RAINFALL EVENT...RELYING MAINLY ON THE ROBUST COOL-SEASON DYNAMICS
AND SUMMERTIME DEEP-LAYER MOISTURE PROFILES...WHEREAS THE STRONGER
INSTABILITY VALUES ARE NOT FORECAST TO COINCIDE WITH THE STRONGEST
FORCING. THUS SHORT TERM RAINFALL RATES (WITHIN 6 HOURS) ARE NOT
EXPECTED TO BE ESPECIALLY HEAVY IN THE MODERATE RISK AREA...BUT
PER MUCH OF THE MODEL GUIDANCE...MUCAPES OF 500-1000+ J/KG ARE
NOTED AS FAR NORTH AS THE I-70 CORRIDOR THIS AFTN AND EARLY
EVENING...WITH HIGHER CAPES FARTHER SOUTH. WPC THEREFORE FELT
COMFORTABLE TO TAKE A CONSENSUS APPROACH WITH THE QPF OVER THESE
AREAS...AS THE GLOBAL GUIDANCE CONTINUES TO GET SUPPORT FROM THE
HIGH-RES MODELS IN NOTING THE MAXIMUM QPF AXIS ALONG AND NORTH OF
THE OH RIVER WHERE THE DEEP-LAYER ELEVATED INSTABILITY...WHILE NOT
AS ROBUST AS COMPARED TO AREAS SOUTH...WILL NEVERTHELESS SUPPORT
AREAS OF HEAVY...POTENTIALLY EXCESSIVE RAINFALL GIVEN THE STRONG
DYNAMICAL FORCING. USING A MULTI-MODEL BLEND...WPC NOTED A RATHER
ELONGATED SWATH OF AREAL-AVERAGE RAINFALL BETWEEN 1-2.5 INCHES
ACROSS EASTERN PORTIONS OF THE MID MS VLY ACROSS THE OH VALLEY AND
INTO THE WESTERN SLOPES OF THE CENTRAL/NORTHERN APPALACHIANS.
HOWEVER...IT SHOULD BE NOTED THAT THE HIGH-RES GUIDANCE (INCLUDING
THE 4KM CONVECTIVE-ALLOWING MODELS) SHOW POCKETS OF HIGHER TOTALS
-- ON THE ORDER OF 3-5 INCHES.

A SLIGHT RISK OF EXCESSIVE RAINFALL SURROUNDS THE MODERATE RISK
AREA...AND REACHES FARTHER SOUTH INTO THE INSTABILITY AXIS WHICH
WILL BE SWEPT BY LOW LEVEL FORCING ALONG A FRONTAL BOUNDARY. FLOW
AT 850 MB IS STRONGLY VEERED...AND LACKS FOCUS...WHICH MAY LIMIT
CONVECTIVE ORGANIZATION AND TRAINING IN THE SLIGHT RISK AREA...AND
MAY EXPLAIN WHY THE HIGH RESOLUTION MODELS HAVE A MORE COHERENT
HEAVY RAIN SIGNAL FARTHER NORTH WITHIN THE DEEP LAYER FORCING. WPC
DID EXTEND THE RISK SOUTH AND EAST TO CATCH THE WARM
FRONT...RECENTLY ENHANCED BY CONVECTIVE OUTFLOWS...ACROSS SOUTHERN
VA AND EASTERN NC. DAYTIME HEATING SHOULD PROVE SUFFICIENT FOR
CONVECTIVE INITIATION GIVEN NEUTRAL UPPER FORCING...AND PW VALUES
ARE ESPECIALLY HIGH ALONG THIS PORTION OF THE FRONT. SOME SPOTS IN
VA/NC RECEIVED 2-3 INCHES OF RAIN ON THURSDAY.



...SOUTHERN ROCKIES AND SOUTHERN HIGH PLAINS...

HIGHLY-DIFFLUENT MID-UPPER LEVEL FLOW EAST OF THE UPPER RIDGE
ALONG WITH THE LOW-LEVEL FRONTAL BOUNDARY SLOWLY DROPPING SOUTH
ALONG THE EASTERN SLOPES OF THE SOUTHERN ROCKIES WILL PROVIDE
SUFFICIENT DYNAMICAL FORCING AND EASTERLY (UPSLOPE) LOW-LEVEL
MOISTURE TRANSPORT (AND ANOMALOUS PW VALUES) FOR MODERATE TO
LOCALLY HEAVY RAINFALL INTO THE SOUTHERN HIGH PLAINS AND ALONG THE
EASTERN SLOPES OF THE SOUTHERN ROCKIES. THE MODELS...PARTICULARLY
THE HIGH-RES GUIDANCE...ALL SHOW POCKETS OF HEAVIER TOTALS (1-3+")
ALONG THE EASTERN SLOPES OF THE SANGRE DE CRISTO MTNS OF
NM...WHICH WILL BE AIDED BY THE AVAILABLE DEEP-LAYER INSTBY WITH
MUCAPES BETWEEN 1000-1500 J/KG. CONSIDERING THE RELATIVELY LOW FFG
OVER THIS REGION (3 HOURLY VALUES AROUND 2.00 INCHES...6 HOURLY
AROUND 2.5 INCHES)...LOCALIZED RUNOFF ISSUES WILL BE LIKELY SHOULD
THESE AMOUNTS VERIFY.


GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV

HURLEY/BURKE
$$




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