Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 240830
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT SAT SEP 24 2016

...VALID 12Z SAT SEP 24 2016 - 12Z SUN SEP 25 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
110 S MRF 15 ESE FST 60 SSW CDS 15 NE WWR 10 SW CNK 20 W SUX
15 ENE MOX 20 E LXL 15 SSE CAV MKC 10 NNW ADH 40 NE JCT
20 NE DLF 70 W MMPG.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NW CYBR MIB 2WX 30 S IKA 10 SE TMH HLD 25 S WRL 25 N GEY
25 SE JDN 20 ENE CWAQ 30 WNW CWBD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
120 S E38 10 SE SNK 25 N CSM 25 NNW EWK 30 WSW FOE 25 NNW CNU
20 SW BVO 15 SW PVJ 35 WSW BWD 15 NNW DLF 90 S 6R6.


...NORTHERN ROCKIES...

CLOSED MID-UPPER LEVEL LOW OVER THE CENTRAL ROCKIES EARLY WILL
SLOWLY LIFT NORTHEAST INTO THE NORTHERN PLAINS TODAY AND TONIGHT.
THE N-S ORIENTED JET STREAK ON THE BACK SIDE OF THE TROUGH WILL
ENHANCE THE MID LEVEL DEFORMATION ON THE BACKSIDE OF THE
TROUGH...EVIDENCED BY THE NARROW N-S VORT LOBE (NARROW AXIS) JUST
BEHIND THE MAIN MID LEVEL VORT CENTER. AS A RESULT...WILL CONTINUE
TO SEE A RATHER ABRUPT END TO THE WESTWARD EXTENT OF THE COMMA
HEAD...THOUGH WHILE RELATIVELY NARROW THE ENHANCED FGEN WILL MAKE
FOR A PRODUCTIVE TROWAL IN TERMS OF PCPN
EFFICIENCY/PRODUCTION...PARTICULARLY THROUGH 00Z SUN. WITH PW
ANOMALIES STILL A HEALTHY 3 TO 4 STANDARD DEVIATIONS ABOVE NORMAL
DURING THAT TIME...THE MODELS (BOTH GLOBAL AND HIGH-RES) CONTINUE
TO DEPICT SOME RATHER ROBUST TOTALS ACROSS NORTHEAST WY INTO
EASTERN MT AND WESTERN ND. USING A MULTI-MODEL CONSENSUS...WPC
NOTED AREAL-AVERAGE AMOUNTS BETWEEN 1-2" ACROSS THIS AREA...WHILE
THE HIGH-RES CAMS SHOW ISOLATED POCKETS OF 3-4" OVER NORTHEAST WY
AND SOUTHEAST MT GIVEN THE UPSLOPE ENHANCEMENT WITH THE 850-700 MB
NORTHERLY FLOW. AS WOULD BE EXPECTED...DEEP-LAYER INSTABILITY WILL
BE SORELY LACKING OVER THIS REGION (AS THUS WILL SHORT-TERM
RAINFALL RATES)...AS CURRENT AND MODEL FORECAST CAPES OF ANY
SIGNIFICANCE (ABOVE 200 J/KG) WERE NOTED FARTHER EAST OF THE
TROWAL/MAX PCPN SHIELD...I.E. FARTHER EAST INTO THE DAKOTAS. AS A
RESULT...THE RISK FOR SHORT-TERM RUNOFF ISSUES WILL BE
MARGINAL/ISOLATED AT BEST.


...CENTRAL-SOUTHERN PLAINS...

A LINE OF MOD-HEAVY RAINFALL IS STILL ON TRACK ALONG AND AHEAD OF
THE COLD FRONT. THE MORE SIGNIFICANT/PROGRESSIVE HEIGHT FALLS WILL
PUSH ACROSS THE NORTHERN PLAINS INTO THE NORTHERN PLAINS DURING
THE PERIOD. GIVEN THE FASTER W-E FRONTAL PROGRESSION ALONG WITH
WEAKER AVAILABLE DEEP-LAYER INSTABILITY...RAINFALL AMOUNTS ACROSS
THE NORTHERN PLAINS INTO THE UPPER MS VALLEY WILL AVERAGE LESS IN
COMPARISON TO THE CENTRAL AND SOUTHERN PLAINS.

DESPITE THE SLOWER UPPER TROUGH/SURFACE FRONTAL PROGRESSION...WPC
DID LEAN TOWARD THE HIGH-RES GUIDANCE (WRF-ARW...NMMB...AND RGEM)
WITH RESPECT TO THE EASTWARD PROGRESSION OF THE HEAVY RAINFALL
AXIS OVER THE CENTRAL AND SOUTHERN PLAINS THIS AFTERNOON INTO
EARLY EVENING...GIVEN THE MORE ROBUST DEGREE OF PRE-FRONTAL
INSTABILITY (DEVELOPING COLD POOLS/OUTFLOW
BOUNDARIES)...INCREASING VERTICAL WIND SHEAR...AND TIGHTENING PW
GRADIENT. HOWEVER... EXPECT AN UPTICK IN PRE-FRONTAL LOW-LEVEL
INFLOW OVERNIGHT...WHILE BECOMING MORE ALIGNED WITH THE MEAN
850-300 MB FLOW. THIS WILL ALLOW FOR AN INCREASED POTENTIAL A
SLOWER QLCS PROGRESSION AND THUS CELL TRAINING...AS NOTED PER THE
WEAKENING CORFIDI VECTORS WHICH THE MODELS SHOW BECOMING MORE
EASTERLY WITH TIME OVERNIGHT (INDICATIVE OF THE INCREASING UPWIND
PROPAGATION). DESPITE THE WEAKENING DEEP-LAYER INSTABILITY DURING
THE OVERNIGHT HOURS...MUCAPES OF 1000-1500 J/KG ALONG WITH THE
FAVORABLE MOIST PROFILE (PWS OF 1.75-2.00") AND HIGHER LIKELIHOOD
OF CELL TRAINING WILL BE MORE THAN SUFFICIENT TO SUPPORT A SLIGHT
RISK IN THE EXCESSIVE RAINFALL OUTLOOK. IN TERMS OF THE QPF...WPC
UTILIZED A MULTI-MODEL ENSEMBLE WITH THE AREAL-AVERAGE AMOUNTS
(MAX STRIPE OF 1-1.5")...HOWEVER THE HIGH-RES CAMS SHOW POCKETS OF
MUCH HIGHER TOTALS (3-6") GIVEN THE AFOREMENTIONED FAVORABLE
THERMODYNAMIC AND KINEMATIC PROFILE...ESPECIALLY LATE SAT INTO
EARLY SUN.

HURLEY
$$





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