Quantitative Precipitation Forecast
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406
FOUS30 KWBC 120045
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
844 PM EDT FRI AUG 11 2017

...VALID 01Z SAT AUG 12 2017 - 12Z SAT AUG 12 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N RQE 45 SSE DRO 20 SSW CPW 25 NNW ALS 30 SW FCS 25 NNE LHX
35 NE SPD 25 NW GAG 15 SSE WWR 25 SSW END 15 ENE SNL 30 N MLC
10 N LRF 15 ESE DYR 10 NNE MQY 15 WNW CHA 20 SSW ALX 10 NE NSE
10 SSW GPT 30 ESE ACP 25 SSE PSN 15 W MWL 25 WSW SPS 15 ENE CDS
35 ESE CVN 15 S ATS 15 W MMCS 10 ENE DMN 40 NW SVC 25 W SAD
20 NE DMA 20 WNW TUS 40 SSW CGZ 15 SE GBN 20 W GYR 55 WSW PRC
10 SE IFP 35 E NXP 25 SSE DAG 35 S DRA 25 NW SGU BCE 25 NE GCN
60 NNE INW 30 N RQE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSE MLJ 25 NW MLJ 25 ENE GVL 20 NNW AVL 15 SE BCB RIC NGU
20 SSE ASJ POB 25 WSW UDG 30 N JYL 10 SSE MLJ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE CDW 10 W PTW NAK 20 NW 2W6 10 WNW HEF 20 NW HGR
15 WSW LBE 35 NNE PKB 15 WNW ILN 25 SE MIE 15 SE BJJ 10 ENE FIG
30 SSW UCA 30 SSW ALB 20 NNE CDW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ESE INW 25 SSW GUP 20 WSW 4SL 30 SSW ALS 15 ESE VTP
35 SW EHA 10 SW PYX 25 S HHF 35 S PPA 30 NW CVS 15 S SRR
35 WNW HMN 40 NNW TCS 65 SSE SJN 45 SE SOW 30 SSW SOW 50 W SOW
60 SSE FLG 25 S FLG 15 WNW FLG 25 NNE FLG 20 NNE FLG 20 ESE FLG
15 ESE INW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 WSW GTR 25 NE CBM 15 NE MSL 20 ENE MDQ 60 S TCL 15 SSE MCB
20 S IER 15 SSE 4F4 30 NW HKS 35 WSW GTR.


...01Z EXCESSIVE RAINFALL OUTLOOK...

GIVEN THE MODIFICATIONS MADE AROUND 21Z...FEW CHANGES WERE MADE TO
EXISTING SLIGHT RISK/MARGINAL RISK AREAS.  00Z SOUNDING DATA STILL
SHOWED A MOISTURE RICH ATMOSPHERE IN PLACE FROM THE SOUTHEAST
STATES BACK TOWARDS THE CENTRAL/SOUTHERN PLAINS.

PRECIPITABLE WATER VALUES WERE NOT AS HIGH FROM THE MID ATLANTIC
INTO THE NORTHEAST...BUT MID/UPPER LEVEL DYNAMICS WERE STRONGER
GIVEN DIFLUENT FLOW BETWEEN A MID LEVEL CIRCULATION OVER THE GREAT
LAKES AND RIDGING OVER THE SOUTHEAST STATES. MOST CELLS ALIGNED
WITH THE FLOW AND HAVE HAD THE POTENTIAL FOR TRAINING HAVE NOT
GENERALLY RESULTED IN LARGE RAINFALL AMOUNTS...ALTHOUGH A FEW
CELLS HAVE MANAGED TO SUSTAIN MOIST INFLOW AND HAVE PRODUCED SOME
LOCAL 2 TO 4 INCHES OF RAIN.  MADE A FEW MODIFICATIONS TO THE
WESTERN BOUNDARY OF THE MARGINAL RISK GIVEN WARMING CLOUD TOP
TEMPS...BUT MADE NO CHANGES OVER NY WHERE 1 AND 3 HOUR FLASH FLOOD
GUIDANCE IS LOW.

THE OTHER AREA OF CONCERN FOR FLOODING EXTENDED FROM AZ ACROSS NEW
MEXICO INTO PARTS OF THE TX PANHANDLE.  LAYERED PRECIPITABLE WATER
SATELLITE IMAGERY SHOWED A CLASSIC T CONFIGURATION IN THE MOISTURE
FIELD WITH WATER VAPOR IMAGERY SHOWING A WELL DEFINED WAVE
UPSTREAM CAPABLE OF SUPPORTING THE CONVECTION INTO THE NIGHT.

BANN


...21Z UPDATE...

UPDATED THE EXCESSIVE RAINFALL OUTLOOK.  ONE CHANGE WAS TO
INTRODUCE A MARGINAL RISK OVER PORTIONS OF THE MID ATLANTIC/NY
GIVEN SLOW CELL MOTION OBSERVED ON RADAR...THE LOCATION OF LOWER
FLASH FLOOD GUIDANCE ESPECIALLY OVER PLACES LIKE THE
CATSKILLS...AND TERRAIN.  SHORT TERM RADAR ALSO SUGGESTED SHIFTING
A SLIGHT RISK FROM AR EASTWARD INTO PORTIONS OF MS/AL/LA.
PRECIPITABLE WATER VALUES REMAINED AT OR ABOVE 2 INCHES HERE AND
THE SOUNDING PROFILE FROM THE MODELS SHOULD SUPPORT EFFICIENT RAIN
MAKERS IN THIS REGION.  ALSO ADJUSTED THE SLIGHT RISK OVER
PORTIONS OF NM NORTHWARD AND SOUTHWARD GIVEN THE SHORT TERM RADAR
PRESENTATION...THOUGHT THE AREAL COVERAGE SHOULD ONLY EXPAND WITH
THE APPROACH OF THE WAVE SEEN IN WATER VAPOR IMAGERY.

BANN

...SOUTHWEST AND CO/NM ROCKIES TO THE S-CENTRAL PLAINS/MS VALLEY...

SATELLITE DERIVED AND OBSERVED PRECIPITABLE WATER VALUES UPWARDS
OF 2 INCHES REMAIN OVER PORTIONS OF AZ AND MODELS FCST ADDITIONAL
MOISTURE ADVECTING INTO THE SOUTHWEST FROM MEXICO. VORT ENERGIES
ON THE WRN PERIPHERY OF THE RIDGE IN FAVORABLE UPPER
DIVERGENCE/UPPER JET DYNAMICS KEEPS CONVECTION ACTIVE DAY 1 ACROSS
AZ...SRN NV...AND ACROSS NM. THE COMBINATION OF ENHANCED
LIFT/MOISTURE LEADS TO LOCALLY HEAVY DOWNPOURS...WITH LOCAL RUNOFF
PROBLEMS. THE BETTER CLUSTERING OF HIGHER QPF IN THE HIGH RES
MODELS IS IN NM.

FAVORABLE RIGHT ENTRANCE REGION DYNAMICS WILL PERSIST WITH A
CENTRAL PLAINS TO OH VALLEY UPPER JET MAXIMA TODAY....WITH THE
MODELS SHOWING DIFLUENT FLOW ALOFT AND SPORADIC UPPER DIVERGENCE
MAXIMA IN THE LOWER MS VALLEY...CENTERED ON AR. LIFT IS AIDED BY
LOW LEVEL BOUNDARY AND MOISTURE POOLING ALONG THE BNDRY UPWARDS TO
2 STD DEVIATIONS ABOVE NORMAL.  CONVECTION DEVELOPS ALONG THE
LEADING EDGE OF OUTFLOWS FROM THE MORNING COMPLEX EXITING OK
ACROSS AR...AND ALONG THE FRONT IN SOUTHEAST MO.

THE RISK AREA WAS DROPPED ALONG THE RED RIVER STRADDLING SOUTHERN
OK/NORTH TEXAS AS THE TRAILING BANDS OF SHOWERS HAVE BEEN MOSTLY
LIGHT WITH RECENT GUIDANCE SHOWING AMOUNTS MOSTLY UNDER AN INCH.


...SOUTHEAST US/SRN APPALACHIANS...

A PLUME OF MOISTURE WITHIN A LOW-MID LEVEL CONFLUENT ZONE IS
FORECAST FROM THE CENTRAL GULF COAST STATES/TN VALLEY TO THE
SOUTHEAST. WIDESPREAD/HEAVY CENTRAL GULF COAST CONVECTION
DEVELOPED TODAY WITH A FOCUSING MCV. EXPECT ACTIVITY WILL
REDEVELOP TODAY WITH THE SLOW MOVING FEATURE AS THE PLUME OF LEAD
MOISTURE REMAINS IN PLACE AS A WEST-EAST UPPER JET MAXIMA PUNCHES
EWD ACROSS KY FRI. COUPLETS OF UPPER DIVERGENCE/LOWER CONVERGENCE
DEVELOP AND PRODUCE SHOWERS/STORMS ACROSS THE SOUTHEAST/CENTRAL TO
SRN APPALACHIANS...AND ADJACENT LEE AREAS UP THROUGH THE
CAROLINAS/MID-ATLANTIC LATER DAY1 IN ADVANCE OF THE APPROACHING
NRN STREAM COLD FRONT. BELIEVE HEAVIEST THREAT TODAY MAY BE OVER
N-CENTRAL GA/SRN APPALACHIANS/WRN CAROLINAS WITH THE MCV/DEEPEST
MOISTURE...BUT DEEP MOISTURE LINGERS ACROSS MUCH OF THIS REGION
INCLUDING AREAS WET WITH RECENT RAINFALL. THERE IS A MARGINAL RISK
OF EXCESSIVE RAINFALL.


GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV

PETERSEN/SCHICHTEL
$$





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