Quantitative Precipitation Forecast
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FOUS30 KWBC 270007
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
806 PM EDT FRI MAY 26 2017

...VALID 01Z SAT MAY 27 2017 - 12Z SAT MAY 27 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE BBW 10 NW HSI 60 WNW CNK 30 SSW HLC 45 SSE ITR 20 W LIC
DEN 35 E GXY 20 ENE CYS 10 WNW BRX 30 ENE SIB 25 WNW CDR
30 W VTN 35 SW VTN 30 ESE AIA 35 N OGA 20 SSE BBW.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ENE OKK 30 SW AOH 25 SE AOH OSU 15 NE LUK 20 W BAK
30 ESE DNV 20 NE LAF 10 ENE OKK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S IML 30 N MCK 20 W HDE 30 S HDE 10 NE HLC 45 ESE GLD
10 S ITR 25 WNW ITR 35 N ITR 25 S IML.




01Z UDPATE
ONLY MINOR ADJUSTMENTS WERE MADE TO PREVIOUS EXCESSIVE RAIN AREAS
AND REASONING.  MAIN CHANGE TO MARGINAL RISK AREA ACROSS THE OH
VALLEY WAS TO NARROW REGION TO FOCUS MAIN HEAVY RAIN THREAT ALONG
WARM FRONTAL BOUNDARY WHERE VERY SMALL SCALE BUT INTENSE TSTM
CLUSTER HAS BEEN MAINTAINED ALONG NRN EDGE OF 500-1000 J/KG MLCAPE
GRADIENT...MAINLY THROUGH THE EARLY OVERNIGHT PD. SULLIVAN


...FRONT RANGE INTO THE CENTRAL HIGH PLAINS...

WATER VAPOR SHOWS A CIRCULATION DEVELOPING IN SOUTHERN ID.  AS THE
CIRCULATION MOVES EAST THROUGH TONIGHT TOWARDS WY...THE ASCENT
CAUSED BY STEEPENING 700-500 MB LAPSE RATES AND STRENGTHENING
DIVERGENCE ALOFT TRIGGERS SHOWERS/STORMS ACROSS WY AND NORTHEAST
UT THAT MOVE DOWNSTREAM ACROSS THE PLAINS OF NE AND NORTHEAST CO
AND NORTHWEST KS.
AS PW VALUES CLIMB TO NEAR 1.25 " INTO NORTHWEST KS...ENHANCED LOW
LEVEL CONVERGENCE OCCURS ON THE NOSE OF THE LOW LEVEL
JET...FAVORING AN INCREASE IN SHOWERS/STORMS EXITING NORTHEAST CO
ACROSS NORTHWEST KS. A SLIGHT RISK REMAINS AS THE SE-S LOW-LEVEL
INFLOW (~40 KTS) ARE EXPECTED TO SUPPORT WIDESPREAD RAINS WHERE
THE RELATIVELY LOW FLASH FLOOD GUIDANCE EXISTS. MOST FORECASTS
INDICATE 1-2 INCHES OF RAIN ACROSS THE AREA.

MANY PIECES OF GUIDANCE...PARTICULARLY HIGH-RES/CAMS... CONTINUE
TO SHOW A BI-MODAL DISTRIBUTION WITH THE QPF (2 DISTINCT
MAXIMA)...ONE ACROSS NORTHEAST CO EASTWARD INTO SOUTHWEST
NE-NORTHWEST KS (BETTER THERMODYNAMICS) WITH ANOTHER FARTHER NORTH
ACROSS SOUTHEAST WY EASTWARD INTO WESTERN NE (BETTER DYNAMICS).
WPC CONTINUED WITH THIS IDEA WHEN COMPOSING THE QPF...LEANING
TOWARD THE HIGH-RES MODELS WITH THE LOCATION/AMOUNTS WITH THE
SOUTHERN AXIS...WHILE ENCOMPASSING A WIDER ARRAY OF GUIDANCE
FARTHER NORTH.

...MID MISSISSIPPI AND OHIO VALLEYS...

THE GFS IS A DECIDED OUTLIER WITH RESPECT TO THE
CONVECTIVELY-ENHANCED SHORTWAVE LIFTING ACROSS THE UPPER MS VALLEY
AND UPPER GREAT LAKES TONIGHT...AS THE GFS IS A DECIDED NORTHERN
OUTLIER WITH THE STRIPE OF QPF. AT THE SAME TIME...EVEN THE
NON-GFS GUIDANCE SHOWS A FAIR AMOUNT OF SPREAD...BOTH IN TERMS OF
LOCATION (N-S) AND AMOUNTS ACROSS THE OH VALLEY TO THE ADJACENT
SOUTHERN LAKES.

THE HIGH-RES CAMS (RGEM...WRF-ARW...NMMB...AND NSSL WRF) ARE
PROBABLY TOO HEAVY WITH THEIR HIGHEST AMOUNTS GIVEN THE SHORT
DURATION PLUS FAIRLY MODEST STRENGTH OF LOW LEVEL INFLOW INTO THE
DEVELOPING ACTIVITY.  ACTIVITY TYPICALLY DEVELOPS INTO THE AXIS OF
THE HIGHER AVAILABLE MOISTURE AND LOW LEVEL JET...WHICH IN THE GFS
IS IN IN...WHICH WOULD BRING IT INTO BETTER AGREEMENT WITH THE
OTHER MODELS DEVELOPING ACTIVITY FURTHER SOUTH. THE MORNING UPDATE
WAS PRIMARILY TO EXPAND THE MARGINAL RISK TO ENCOMPASS SOLUTIONS
OUTSIDE THE PRIOR AREA...LIKE THE NSSL WRF AND THE EMC ADAPTATION
OF THE NSSL WRF.

WPCQPF WAS FAIRLY CLOSE TO A BLEND OF THE 00Z UKMET AND
ECMWF...WHICH NOTED MAXIMUM AREAL-AVERAGE TOTALS BETWEEN 0.50-1.0
INCH. GIVEN THE WET ANTECEDENT SOILS/LOW FFG VALUES (IN SOME AREAS
AS LOW AS ONE INCH IN 3 HOURS)...WPC WILL CONTINUE WITH THE
"MARGINAL" RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
IN-OH-ADJACENT NORTHERN KY. THE AREA HAS SOMEWHAT REDUCED FLASH
FLOOD GUIDANCE FROM THE MID WEEK RAINFALL...SO WILL NEED TO BE
MONITORED IN CASE HEAVIER RAINS DO DEVELOP.

PETERSEN

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