Quantitative Precipitation Forecast
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000
FOUS30 KWBC 191454
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1054 AM EDT WED JUL 19 2017

...VALID 15Z WED JUL 19 2017 - 12Z THU JUL 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
95 NNW MMHO 75 SSE GBN 10 ESE CGZ DVT 50 WNW LUF 35 NE YUM
25 S IPL 20 NNW CZZ 20 W PSP 55 NNE DAG 40 ENE DRA 85 NE DRA
45 SSW ELY 50 NE ELY 25 SE DPG 30 NNE FIR 25 NNE BIT 15 SSE CPR
15 W SIB 30 E ARL 15 WNW FNL 20 W MNH 15 ENE CPW 15 N FMN
20 NNW RQE 40 WNW RQE 70 NNE INW 35 NNE INW 15 WNW SJN
65 WNW TCS HMN 20 SSW CNM 10 S FST 30 SSW 6R6 115 SSW 6R6
120 SE MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 W LNL 10 NNW MNM 35 WSW MKG 10 WSW IGQ MQB 25 E EBS
15 SSW FSD 25 E ANW 30 N VTN PIR 35 S MBG 15 WNW MBG 50 NE HEI
30 SSE KS25 15 SW K08D 10 W K5H4 20 SW FSE 20 N HZX 20 W ASX
10 W LNL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 E JMR 10 SW ATW 15 S BUU 15 SSE SFY 15 SE CCY 25 NNW OTG
40 SW ABR 40 WNW K2D5 20 NE FFM 10 E JMR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
80 N MMHO 40 WNW OLS 30 NNW DMA 30 WSW SAD 30 N DUG 20 SE DUG
65 SSE DUG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 NE PGA 20 SE 40G 30 W PRC 25 ESE EED 15 S HND 55 W SGU
40 SE ELY 25 NE U24 25 SSE FIR 20 ENE VEL 35 W GJT 40 ESE 4HV
40 NE PGA.


15 UTC UPDATE...

MINOR ADJUSTMENTS WERE MADE BASED UPON CURRENT SATELLITE/RADAR
TRENDS...INCLUDING REMOVING SOME OF THE WESTERN EXTENT OF THE
NORTHERN PLAINS MARGINAL AREA.  BUT OVERALL...NO SIGNIFICANT
CHANGES TO THE PREVIOUS OUTLOOK.

PREVIOUS DISCUSSIONS...

1230 UTC SPECIAL UPDATE...

ACROSS THE SOUTHWEST...EXTENDED THE MARGINAL RISK FURTHER WEST
INTO SOUTHERN CA...WHERE A PAIR OF MCVS INTERACTING WITH ANOMALOUS
MOISTURE CONTINUE TO GENERATE CONVECTION...WITH SHORT-TERM
RAINFALL RATES OF 1.5-2.5 IN/HR POSSIBLE.  REFER TO WPC MPD #510
(VALID THROUGH 1530 UTC) FOR FURTHER INFO ON THE SHORT-TERM THREAT.

ACROSS THE NORTHERN PLAINS...EXTENDED THE MARGINAL RISK FURTHER
NORTHWEST ACROSS WESTERN ND INTO FAR EASTERN MT.  INDIVIDUAL CELL
MOTIONS HAVE BEEN PROGRESSIVE...LIMITING THE FLASH FLOOD
THREAT...HOWEVER...CELL TRAINING AND MERGING CELLS MAY RESULT IN
LOCALLY HEAVY ACCUMULATIONS...RESULTING IN LOCALIZED SHORT-TERM
CONCERNS.

...NORTHERN PLAINS / UPPER MIDWEST...

MODELS STRONGLY SIGNAL A PROGRESSIVE MCS EVENT / SEVERE WIND EVENT
PER STORM PREDICTION CENTER OUTLOOK AND CONFIRMED THROUGH
SIMULATED REFLECTIVITY AND QPF SWATHS FROM THE HI-RES RUNS.
DESPITE FAST MOVEMENT...THE ENVIRONMENT IS CHARACTERIZED BY
TYPICAL SUMMERTIME MOISTURE CONTENT AND STRONG INSTABILITY CAPABLE
OF SUPPORTING VERY HEAVY SHORT TERM RAIN RATES IN ADDITION TO THE
SEVERE WEATHER THREAT. A NEWLY ARRIVED FRONTAL ZONE WILL STALL
ACROSS SD/IA/IL. WITH VERY HOT AND DEEPLY MIXED CONDITIONS SOUTH
OF THE FRONT...THE CORRIDOR MORE FAVORABLE FOR ORGANIZED
THUNDERSTORMS SHOULD BE TO THE NORTH OF THE BOUNDARY...ALIGNING
WITH THE BEST OVERLAP BETWEEN THE CONFLUENT MID LEVEL / 700 MB
FLOW TO THE REAR OF A 100-PLUS KNOT UPPER JET AND THE NORTHWARD
RETURNING / SURGING CAPE GRADIENT ALONG THE FRONT. THIS POINTS
TOWARD CONVECTION ORGANIZING AND FANNING OUT / PROPAGATING
DOWNSTREAM OUT OF EASTERN NORTH DAKOTA AND EASTERN SOUTH DAKOTA
INTO SOUTHERN MN AND POINTS BEYOND. THE LATITUDE IS ALWAYS A
DIFFICULT ASPECT OF THE FORECAST. IN THIS CASE THE CONVECTION
SHOULD STRIKE SOME BALANCE BETWEEN EASTWARD PROPAGATION IN DEEP
WESTERLY FLOW...AND SOUTHWARD PROPAGATION TOWARD THE INFLOW AND
CAPE GRADIENT. AFTER COORDINATING WITH LOCAL OFFICES...WPC KEPT
CONTINUITY BY LEANING TOWARD THE SOUTH SIDE OF THE SOLUTION
ENVELOPE...ALTHOUGH WE DID EXPAND THE SWATH AND NUDGE EVER SO
SLIGHTLY NORTHWARD AND EASTWARD. WE ALSO PUSHED HEAVIER AMOUNTS AS
FAR DOWNSTREAM AS POSSIBLE BY 12Z THURSDAY...ASSUMING THE MODELS
WILL NOT QUITE BE FAST ENOUGH WITH WHAT SHOULD BE A PROGRESSIVE
MCS. ONE POSSIBILITY NOT REFLECTED IN THE QPF...HOWEVER...WHICH IS
REFLECTED IN THE EXCESSIVE RAINFALL OUTLOOK...IS THAT THE MCS
COULD TAKE A NOSEDIVE SOUTHWARD IF UPWIND PROPAGATION BECOMES
DOMINANT. THE WRF-ARW AND NSSL WRF IN PARTICULAR INDICATE A RAPID
PLUNGE THROUGH EASTERN IOWA. MARGINAL AND SLIGHT RISK CONTOURS ARE
THEREFORE DRAWN LIBERALLY TO THE WEST OF THE DETERMINISTIC QPF
SWATH TO ACCOUNT FOR THIS POSSIBILITY.

WITH A PROGRESSIVE EVENT LIKE THIS THE FLASH FLOOD RISK WILL BE BE
TIED MORE TO THE INTENSE SHORT TERM RATES POSSIBLE WITH
ANOMALOUSLY HIGH MOISTURE CONTENT AND MODERATE TO STRONG
INSTABILITY. SOME TRAINING COULD OCCUR LATER WED NIGHT OVER PARTS
OF MN/IA/WI AS THE LOW LEVEL INFLOW VEERS AND BECOMES MORE
PERPENDICULAR TO WHAT SHOULD BE AN ESTABLISHED OUTFLOW BOUNDARY.


...SOUTHWEST...

IT LOOKS LIKE A TYPICAL MONSOON DAY. TOTAL COLUMN MOISTURE IS A
LITTLE GREATER OUT OVER THE DESERTS AND EXTENDING UP INTO
SOUTHEAST NEVADA / NORTHWEST ARIZONA AND SOUTHERN UTAH. WIND
SPEEDS ARE ALSO SLIGHTLY ENHANCED IN THAT AREA OWING TO A WEAKLY
DEFINED TROUGH DRIFTING AROUND THE RIDGE. THIS FEATURE WILL LEND A
LITTLE GREATER ORGANIZATION TO THE CONVECTION THAT IS ABLE TO FORM
WHEREVER POCKETS OF HEATING / REDUCED CLOUD COVER ALLOW FOR IT.
MOISTURE WILL ALSO BE SUFFICIENT FOR SCATTERED TO NUMEROUS STORMS
OVER SOUTHEAST ARIZONA AND OVER CENTRAL TO WESTERN COLORADO.
MOISTURE DEPTH AND CLOUD BASE INFLOW MAY INCREASE LATE IN THE
PERIOD OVER EASTERN UTAH WITH ARRIVAL OF THE SMALL TROUGH FEATURE.
OVERALL...SOME OF THE MORE FAVORABLE TIMING OF FEATURES APPEARS TO
OCCUR IN AZ/NV/UT FOR A LITTLE GREATER RISK OF HEAVY DOWNPOURS /
FLASH FLOODING...AND MAINTENANCE OF A SLIGHT RISK OF EXCESSIVE
RAINFALL. THE HIGHER TERRAIN IN SOUTHEAST ARIZONA ALSO REMAINS IN
SLIGHT RISK. BROAD MARGINAL RISK COVERS AREAS FROM CENTRAL
COLORADO DOWN TO SOUTHWEST TEXAS...BUT PARTS OF COLORADO SAW A
CATEGORY DOWNGRADE...COORDINATED WITH WFO PUB AND GJT...GIVEN VERY
LITTLE SUPPORTIVE QPF AND NEAR CLIMATOLOGICAL MOISTURE. ACTIVITY
IN COLORADO MAY INCREASE IN INTENSITY AND COVERAGE BY FRIDAY PER
THE DAY 2-3 PORTION OF THE WPC QPF DISCUSSION...QPFPFD.

PEREIRA/BURKE
$$




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