Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 260836
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT FRI MAY 26 2017

...VALID 12Z FRI MAY 26 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 ESE LBF 10 W HSI 60 WNW CNK 30 SSW HLC 45 S GLD 25 SE LIC
30 NW LIC 35 E GXY 20 ENE CYS 10 WNW BRX 30 ENE SIB 10 N CDR
15 S IEN 20 E BFF 30 ENE SNY 20 ESE LBF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
SGH 15 NW WMO IND 30 S LAF 10 WSW LAF 25 NNE LAF 20 S ASW
25 W AOH 25 SSE AOH SGH.

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


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

THE POSITIVELY TILTED UPPER TROUGH OVER THE CENTRAL GREAT BASIN
WILL ONCE AGAIN SPARK LATE DAY CONVECTION OVER THE FRONT RANGES
AND CENTRAL HIGH PLAINS...AIDED BY THE STEEPENING 700-500 MB LAPSE
RATES AND STRENGTHENING DIVERGENCE ALOFT WITHIN MODESTLY DIFFLUENT
UPPER LEVEL FLOW. BETWEEN 00-12Z SAT...AN UPPER JET STREAK WILL
LIFT ACROSS THE DAKOTAS...PLACING THE FRONT RANGE AND CENTRAL HIGH
PLAINS WITHIN THE FAVORABLE RIGHT ENTRANCE REGION. THE MODELS
RESPOND WITH A RATHER ROBUST AREA OF ENHANCED UPPER
DIVERGENCE/DEEP-LAYER ASCENT...ALBEIT EXHIBIT N-S DIFFERENCES.
MOREOVER...THERE WILL ALSO BE A FAIRLY SHARP N-S INSTABILITY
GRADIENT ALONG/NEAR THE KS-NE BORDER OVERNIGHT... AS PW VALUES
CLIMB TO AOA 1.25 " INTO NORTHWEST KS. IN A PATTERN SUCH AS
THIS...AT LEAST ONE AREA OF WIDESPREAD CONVECTION IS FAVORED
FARTHER SOUTH INTO THE MORE THERMODYNAMICALLY-RICH AIRMASS (HIGHER
CAPE/PW)...YET STILL CLOSE ENOUGH (ON THE SOUTHERN PERIPHERY) TO
BENEFIT FROM THE UPPER JET STREAK TRAVERSING THE NORTHERN PLAINS.
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.

IN TERMS OF THE DAY 1 EXCESSIVE RAINFALL OUTLOOK...WILL MAINTAIN A
MORE ELEVATED RISK ("SLIGHT") OVER MORE OR LESS THE SAME AREA AS
WITH THE DAY 2 ERO FROM YESTERDAY. THIS IS ASSOCIATED WITH THE
SOUTHERN PCPN MAXIMA...WHERE THE AFOREMENTIONED THERMODYNAMICS AND
SE-S LOW-LEVEL INFLOW (~40 KTS) ARE EXPECTED TO BE MOST FAVORABLE
FOR POTENTIALLY EXCESSIVE 1-3 HOURLY RAINFALL RATES CONSIDERING
THE RELATIVELY LOW FFG.


...MID MISSISSIPPI AND OHIO VALLEYS...

AS NOTED IN THE PMDHMD...THE GFS IS A DECIDED OUTLIER WITH RESPECT
TO THE REMNANT MESO/CONVECTIVELY-ENHANCED SHORTWAVE LIFTING ACROSS
THE UPPER MS VALLEY AND UPPER GREAT LAKES TODAY AND TONIGHT. THE
OTHER MODELS AREN`T NEARLY AS BULLISH (I.E. DENOTE A FLATTER
WAVE)...AND AS SUCH...THE GFS IS A DECIDED WET AND 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...ALONG A QUASI WEST-TO-EAST AXIS. FEEL
SOME OF THE HIGH-RES CAMS (RGEM...WRF-ARW...NMMB...AND PARALLEL
VERSIONS IN PARTICULAR) ARE PROBABLY TOO HEAVY WITH THE AMOUNTS
BETWEEN I-70 AND I-80...GIVEN THAT THE GREATER DEEP-LAYER
INSTABILITY (TIGHTER CAPE GRADIENT) AND STEEPER 700-500 MB LAPSE
RATES ARE DISPLACED WELL SOUTH OF THE DAMPENING MCV TRACK. 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.

HURLEY

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