Quantitative Precipitation Forecast
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FOUS30 KWBC 121352
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
952 AM EDT SAT JUL 12 2014

...VALID 15Z SAT JUL 12 2014 - 12Z SUN JUL 13 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W LVS 30 ESE 4SL 15 NNE 4SL 20 SSW E33 30 NW CPW 15 WSW MYP
25 NNE CCU 20 E 20V 30 SSW ARL 25 NE LAR 25 WSW SIB SIB
15 NE TOR 15 SSW BFF 30 SSW IBM 20 SE AKO GLD 40 NE LAA
25 WSW LAA 45 E TAD 25 E RTN 25 SW RTN 20 W LVS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
ONZ 25 S DFI 15 WSW GEZ 10 N FOA 25 SW PIA 10 WSW EOK 25 W CDJ
40 NE MHK 45 N RSL 25 SE HDE 20 SSE LNK 20 ENE RDK 20 NNW CIN
25 SW FSD 25 ESE HON 25 NNE BKX 20 S GYL 10 NNE LSE 15 WSW MTW
20 SE TVC 15 NE OSC 30 NE CWGD 15 SE CTZR ONZ.


...15Z UPDATE...

WPC KEPT THE TWO SLIGHT AREAS AND SEE TEXT INTACT FOR THE NEXT 21
HRS AND ONLY MADE SOME SLIGHT MODIFICATIONS TO THE TWO SLIGHT
REGIONS BASED ON LATE OVERNIGHT GUIDANCE AND CURRENT/NOWCAST
CONDITIONS. A FEW HIGHLIGHTS... EXPANDED THE SLIGHT RISK OVER
IL/IN WITH CONVECTIVE HEAVY RAIN CLUSTER MERGING WITH WARM
ADVECTION/ISENTROPIC STEADY RAINS. THE GUIDANCE IS NOT HANDLING
THIS REGION VERY WELL BUT FEELING IS THE CURRENT ORGANIZED RAINS
WILL PERSIST IN NORTH/EASTERN IL BEFORE MOVING INTO NRN/CENTRAL IN
BEFORE POTENTIALLY DISSIPATING LATER THIS AFTN. ALSO EXTENDED THIS
SLIGHT RISK INTO SERN SD/SRN MN IN ANTICIPATION OF STRONG UPPER
JET DYNAMICS WITH THE SURFACE COLD FRONT EXPANDING CURRENT STEADY
RAINS BEFORE ADVANCING DOWNSTREAM LATER TODAY OVER ERN IA/NRN IL
AND SRN WI BACK SWWRD BACK TOWARD NRN KS. THE OTHER SLIGHT RISK
AREA... CONDITIONS LOOK FAVORABLE AND GUIDANCE CAPTURES POSSIBLE
ORGANIZED DIURNAL ACTIVITY OVER EAST CENTRAL CO MTNS BEFORE
POTENTIAL PROGRESSING TOWARD ERN CO/WRN KS AND SOUTH INTO SRN/SERN
CO WITH WPC ATTEMPTING TO NARROW THE ZONE CLOSER TO THE
TOPOGRAPHY. THE EARLIER DISCUSSION IS BELOW.     MUSHER

...MIDWEST...

AN ACTIVE PERIOD IS IN STORE DURING DAY 1...WITH MULTIPLE
OPPORTUNITIES FOR MODERATE/HEAVY RAINFALL WITH THE POTENTIAL FOR
LOCALLY EXCESSIVE AMOUNTS. EARLY SATURDAY...WIDESPREAD ELEVATED
CONVECTION ASSOCIATED AHEAD OF A CONVECTIVELY-FUELED VORT MAX THAT
YESTERDAY WAS IN THE GREAT BASIN WILL CONTINUE TO FEED OFF OF A
POCKET OF FVRBL THERMODYNAMICS WITHIN A RELATIVELY NARROW CORRIDOR
NORTH OF THE W-E SFC BNDRY. PWATS BTWN 1.75-2.00 INCHES ALONG WITH
ELEVATED CAPES BTWN 2000-3000 J/KG WILL CONTINUE TO PRIME THE
REGION AS THE UPPER FORCING INCREASES WITH THE APPROACHING
SHORTWAVE. THE SETUP IS FVRBL FOR A MADDOX "FRONTAL" TYPE HEAVY
RAINFALL EVENT...THOUGH ONE LIMITATION WILL BE THE
FORWARD/DOWNWIND PROPAGATION OF THE CELLS THIS MORNING NORTH OF
THE LLVL FRONTAL BNDRY...AND THE RELATIVELY SWIFT PROGRESSION OF
THE MCV WHICH SHOULD LIMIT THE AMOUNT OF CELL TRAINING FROM THE
WEST AFTER ~12Z SAT AS THE NOCTURNAL LLJ WEAKENS.

NEVERTHELESS...THE EXCESSIVE RAINFALL POTENTIAL WILL BE ENHANCED
BY THE APPROACHING ANOMALOUS LONGWAVE TROUGH...WITH THE ENSUING
HEIGHT FALLS AND INCREASING RIGHT ENTRANCE REGION UPPER JET
DYNAMICS (STRENGTHENING LOW-MID LEVEL FRONTOGENESIS) PROVIDING A
SIGNIFICANT DYNAMICAL BOOST LATER IN THE PERIOD WHEN PRE-FRONTAL
DEEP-LAYER INSTBY (MUCAPES AT LEAST 1000-2000 J/KG) AND AVAILABLE
MOISTURE (PWATS 1.75-2.00 INCHES) REMAIN QUITE FAVORABLE. GIVEN
THE UPPER HEIGHT FALLS AND STRENGTHENING BAROCLINIC/THETA-E/PWAT
GRADIENT...HIS ACTIVITY SHOULD ALSO BE RATHER PROGRESSIVE
(DOWNWIND PROPAGATING)...HOWEVER GIVEN THE COMBINATION OF BOTH
ANOMALOUS DYNAMICAL AS WELL AS THERMODYNAMICAL SUPPORT...EVEN
SHORT-LIVED HIGH RAINFALL RATES (2-2.5 INCHES/HOUR) COULD APPROACH
IF NOT EXCEED 1-3 HOUR FLASH FLOOD GUIDANCE IN SOME AREAS.

...CENTRAL/SOUTHERN ROCKIES AND CENTRAL HIGH PLAINS...

THE PERSISTENCE OF HIGH PWATS (AROUND 2 STANDARD DEVIATIONS ABOVE
NORMAL) STRETCHING WSW FROM THE MIDWEST INTO THE CENTRAL/SOUTHERN
ROCKIES ALONG WITH A SLOW MOVING SHEAR AXIS/REGION OF BROAD UPPER
LEVEL DIFFLUENCE BTWN THE CLOSED UPPER HIGH ACROSS THE CENTRAL
GREAT BASIN AND THE DEEPENING LOW ACROSS SOUTH-CENTRAL CANADA WILL
SET THE STAGE FOR NUMEROUS OROGRAPHICALLY-ENHANCED CONVECTIVE
CLUSTERS LATER SAT AFTN AND EVENING. ACCORDING TO SEVERAL MODEL
SOURCES (INCLUDING SOME OF THE HIGHER RESOLUTION GUIDANCE)...THE
ACTIVITY COULD VERY LIKELY GET HUNG UP AT THE TAIL END OF THE
SURFACE FRONT LATER TONIGHT/EARLY SUN EVEN AS THE MUCAPES
DECREASE...GIVEN THE CONTINUED UPPER LEVEL DIFFLUENCE (SLOW MOVING
CONVECTIVELY-AIDED MCV/SHEAR AXIS) AS THE UPPER LEVEL HEIGHT FALLS
REMAIN WELL NE-E. WPC AGAIN INCORPORATED A MULTI-MODEL BLEND WITH
THE QPF...INCLUDING SOME OF THE HIGHER RESOLUTION GUIDANCE...WHICH
YIELDED SOME IMPRESSIVE AREAL-AVERAGE AMOUNTS (0.5-1.5+ INCHES)
ACROSS THE EASTERN SLOPES OF THE CENTRAL ROCKIES INTO THE CO FRONT
RANGES. FURTHERMORE...SOME OF THE HIGH-RES MODELS SHOW ISOLATED
AREAS IN THE CO FRONT RANGE RECEIVING OVER 5 INCHES...INCLUDING
THE PARALLEL VERSION OF THE 4KM NAM CONEST AS WELL AS THE RGEM.
THIS SETUP HAS THE MAKINGS FOR A POTENTIALLY SIGNIFICANT EVENT
OVER THE CO FRONT RANGE...AS PER FURTHER EVALUATION THIS AREA MAY
BE UPGRADED TO A MODERATE RISK FOR EXCESSIVE RAINFALL LATER TODAY.

...SOUTHWEST...

MONSOONAL CONVECTION LATER THIS AFTN/EVENING SHOULD BECOME BETTER
ORGANIZED (MORE NUMEROUS) ALONG THE SOUTHERN MOGOLLON RIM (AZ/NM
BORDER)... AT LEAST INITIALLY BEFORE SPREADING OUT A BIT ACROSS
EAST-CENTRAL AZ AND WEST-CENTRAL NM. THIS IS AN AREA WHERE THE
MODELS ARE NOTING THE STEEPEST MID LEVEL LAPSE RATES (7-8 C/KM
BTWN 700-500 MB)...HOWEVER LIMITED DEEP LAYER INSTBY (MUCAPES
500-1000 J/KG) WITH THE RELATIVELY DEEP SUB-CLOUD LAYER SHOULD
LIMIT THE COVERAGE/POTENTIAL OF EXCESSIVE RUNOFF.
NEVERTHELESS...LOCALIZED RAINFALL AMOUNTS OVER 2 INCHES ARE NOTED
IN SOME OF THE MESOSCALE GUIDANCE.

HURLEY
$$





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