Quantitative Precipitation Forecast
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000
FOUS30 KWBC 280842
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
442 AM EDT WED JUN 28 2017

...VALID 12Z WED JUN 28 2017 - 12Z THU JUN 29 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S KBQX 20 SE PSX 10 E 5R5 10 ESE IAH 10 NW CWF 25 S BTR
20 ENE NBG 10 NNE KMIS 30 SSW KVKY 15 N CYD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N INL 25 ENE ELO 25 WSW CMX 20 NW ERY 20 ENE ANJ 25 NE CYZE
40 SW CWWX 25 SW RQB MDW 40 SE IRK 15 SSE IXD 30 E SLN 30 SW CNK
25 NW CNK 20 ENE BIE 15 S BNW TOB 25 NE RZN 20 NNW DLH 20 NW HIB
10 S FSE 15 NNE CKN 25 SW ROX 20 S FGN 30 N INL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW ICL IKV DEH 10 ESE MDZ 10 S ERY 20 NNE DRM 10 NE CWNL
10 SE APN 15 SE LDM 10 N PWK 15 W MQB 35 NNW SZL 10 WNW LWC
40 SW FNB 15 SSW ICL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 S KCMB 20 WSW KCMB 10 ENE KVBS 10 W 7R5 10 N 7R5 15 ESE LCH
15 NW 7R4 10 N PTN 20 ENE 7R3 15 SSW NBG 20 NNE AXO 15 ENE AXO
15 SSE AXO 10 SSE 9F2.


...UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES...

A LOW TO MEDIUM AMPLITUDE SHORTWAVE TROUGH EMERGING FROM THE
NORTHERN HIGH PLAINS WILL BE THE PRIMARY DRIVER FOR CONVECTION
TRAVERSING THE UPPER MIDWEST AND WESTERN GREAT LAKES THROUGH
WEDNESDAY NIGHT. THIS AS SURFACE LOW PRESSURE TRACKS EASTWARD
ACROSS CENTRAL MN TODAY...THEN ACROSS NORTHERN WI WEDNESDAY NIGHT.
MEANWHILE...SHORTWAVE ENERGY PIVOTING UNDERNEATH THE
ALBERTA-SASKATCHEWAN UPPER SYSTEM WILL AMPLIFY THE TROUGH ACROSS
THE NORTHERN ROCKIES WED NIGHT...ALLOWING FOR A MORE DIFLUENT
PATTERN AND BROADENING UPPER DIVERGENCE DOWNSTREAM INTO THE PLAINS
AND MO VALLEY. THIS WILL SET THE STAGE FOR ADDITIONAL MCS ACTIVITY
(RESULTANT MCV) THAT THE GLOBALS SHOW EMERGING INTO THIS REGION
OVERNIGHT WED AS THE DEEP-LAYER FORCING BECOMES MORE FAVORABLE...
WITH THE VORT LOBE ALIGNED MORE-OR-LESS PARALLEL TO THE ELEVATED
WARM FRONTAL ARC AS IT LIFTS INTO EASTERN SD-NE BY 1200 UTC THU.

IN TERMS OF LOCATION/AREAL EXPANSE OF THE MORE APPRECIABLE
RAINFALL TOTALS...THE GLOBAL AND HIGH RESOLUTION MODELS CONTINUE
TO CLUSTER REASONABLY WELL. HOWEVER...THE CONVECTIVE...WARM SEASON
MODE OF THE EVENT AND ATTENDANT MESOSCALE FEATURES
(MCV/S...OUTFLOW BOUNDARIES) WILL MAINTAIN UNCERTAINTY AT SMALLER
SCALES...PARTICULARLY WITH THE MAXIMA. MOREOVER...FORECAST
CONFIDENCE REMAINS LOWER (ALBEIT IMPROVING) IN TERMS OF HOW FAR
SOUTH THE WED NIGHT-EARLY THU MCS ACTIVITY WILL DROP. ONE OF THE
TRENDS NOTED WITH SOME OF THE 00Z CAM OUTPUT (PARTICULARLY THE
WRF-ARW AND NAM CONUS NEST) WAS A SIGNAL FOR HIGHER TOTALS FARTHER
SOUTH ACROSS THE LOWER MO VALLEY (INTO NORTHEAST KS AND NORTHERN
MO) DURING THE 00-12Z THU TIME FRAME. GIVEN THE PRESENCE OF THE
CONVECTIVELY-AIDED VORT LOBE...AGREE WITH THE SOUTHWARD TREND...AS
EXPECT THE DEEP-LAYER ASCENT TO ERODE THE INITIALLY-CAPPED MID
LAYER CENTERED AROUND 750-700 MB. LARGELY DUE TO THE CONTINUED
MODEL SPREAD WITH RESPECT TO THE LOCATION OF MAX TOTALS...WPC
INCORPORATED A MULTI-MODEL BLEND IN COMPOSING THE QPF...WITH
CONSIDERABLE WEIGHT GIVEN TO THE HREF MEAN AND WRF-ARW. WHILE
AREAL-AVERAGE TOTALS ARE EXPECTED TO REMAIN UNDER 2 INCHES...PER A
BEVY OF HIGH-RES CAM GUIDANCE LOCALIZED AMOUNTS OF 3-6+ INCHES
WILL BE POSSIBLE.

FOR THE DAY 1 EXCESSIVE RAINFALL OUTLOOK...THE SLIGHT RISK AREA
CHANGED LITTLE FROM THE PREVIOUS DAY 2 ERO...WITH THE SLIGHT RISK
ENCOMPASSING THOSE AFOREMENTIONED UPPER-BOUND AMOUNTS PER THE
HIGH-RES CAMS.


...GULF COAST...

A WEAKNESS IN THE MID LEVEL HEIGHT FIELD EXISTS ALONG THE GULF
COAST...SITTING ATOP A STALLED SURFACE FRONTAL BOUNDARY FROM
NORTHERN FLORIDA TO COASTAL TEXAS. THE SITUATION IS FAVORABLE FOR
DIURNALLY ENHANCED SEA BREEZE ACTIVITY NEAR THE COAST AND BROADER
AREAS OF RAIN JUST OFFSHORE AND AHEAD OF THE WEAKLY DEFINED TROUGH
AXIS. THIS IS ESPECIALLY TRUE OVER THE WESTERN GULF /
TEXAS...WHERE THE HI-RES MODELS HAVE SOME INDICATION OF CONVECTION
AND LATENT HEAT RELEASE BEING SUFFICIENT TO FEEDBACK ONTO THE MID
LEVEL FLOW...DEVELOPING A BROAD CIRCULATION. ANY SHOWERS MAY
PRODUCE LOCALLY HEAVY DOWNPOURS...BUT THE BULK OF THE MORE
ORGANIZED RAINFALL WEDNESDAY SHOULD OCCUR IN ASSOCIATION WITH SEA
BREEZES OVER MUCH OF FLORIDA...AND OFFSHORE OF TEXAS AND LOUISIANA
NEAR THE DEVELOPING LOW CENTER.

WED NIGHT INTO EARLY THU...THE MODELS DEPICT A SLIGHT NORTHWARD
SHIFT WITH THE MID-LEVEL SHEAR AXIS/VORT LOBE...BECOMING DRAPED
ALONG THE CENTRAL-EASTERN GULF COAST AS THE WESTERN U.S. TROUGH
AMPLIFIES AND THE SOUTHEAST RIDGE SLIDES A LITTLE FARTHER EAST. AS
A RESULT...EXPECT MORE OF THE CONVECTION OVER THE GULF TO COME
ASHORE ACROSS THE WESTERN AND ESPECIALLY CENTRAL PORTIONS OF THE
GULF COAST. HIGHEST AREAL-AVERAGE TOTALS (2-2.5") WERE NOTED IN A
RELATIVELY NARROW CORRIDOR CLIPPING SOUTHERN LA...THOUGH SOME OF
THE HIGH-RES CAMS CONTINUED TO DEPICT SOME RATHER PRODIGIOUS
TOTALS (4-8+ INCHES) JUST OFFSHORE.

IN TERMS OF THE EXCESSIVE RAINFALL THREAT...A NARROW SLIGHT RISK
AREA WAS ADDED TO FAR SOUTHERN LOUISIANA GIVEN THE AFOREMENTIONED
WETTER TRENDS IN THE GUIDANCE (CAMS ESPECIALLY). A
HIGHLY-FAVORABLE THERMODYNAMIC ENVIRONMENT CHARACTERIZED BY PWS
AOA 2.25" ALONG WITH A DEEP...NARROW DISTRIBUTION OF INSTABILITY
(MUCAPES 1500-2000 J/KG JUST OFFSHORE) WILL MAKE FOR ROBUST WARM
RAIN PROCESSES AND HIGHLY-EFFICIENT SHORT-TERM RAINFALL
RATES...POSSIBLY EXCEEDING 2.5"/HOUR UNDERNEATH THE HEAVIEST
CORES.

HURLEY
$$




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