Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
000
FOUS30 KWBC 201931
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
330 PM EDT SAT AUG 20 2016

...VALID 21Z SAT AUG 20 2016 - 12Z SUN AUG 21 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NW CYSB 55 NNE CYZE GOV 35 ESE MTW 20 ENE CLI 25 NNW IMT
35 NNE CYXZ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
130 ESE MMCU 35 W DRT 40 W E29 40 W SJT 25 SSW DYS 15 W GVT
15 SW JBR 15 NW EVV 15 N AOH 20 SW CLE PIT MGW LWB 35 WSW TNB
10 NW GVL 25 NW BHM 35 SE GLH 35 WSW TVR 15 ENE ESF 30 SSE LFK
VCT 70 S MMMY.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NNW MMMV 15 ESE MMPG 30 S ECU 10 NW JCT 20 NW 05F 10 SSW 4F4
20 E M89 25 NE SGT 35 WSW UTA LLQ 10 SSW MLU 35 N ESF 35 WSW IER
20 NE UTS 35 N ALI 20 E MMMY.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SSE SSF 20 ESE COT 10 NNW COT 15 WNW ERV 20 NNW BMQ
10 ENE HLR 20 W LHB 20 N 62H 45 ESE BAZ 50 SSE SSF.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S BMQ 10 SSE AUS 25 SE BAZ 30 S SSF 30 NNE COT 10 S ERV T82
25 S BMQ.


...20Z SPECIAL UPDATE AND UPGRADE TO HIGH RISK IN TEXAS...
...POTENTIAL FOR A SIGNIFICANT HILL COUNTRY FLASH FLOOD EVENT
OVERNIGHT...

...TEXAS...

GROWING VERY CONCERNED ABOUT THE INGREDIENTS IN PLACE THAT WOULD
SUPPORT A CONVECTIVELY ENHANCED MID LEVEL VORTEX OR MCV...AND THE
ASSOCIATED VERY STRONG TREND TOWARD EXCESSIVE RAINFALL AMOUNTS
TOTALING 10 TO 15 INCHES IN MOST OF THE HIGH RESOLUTION GUIDANCE.
HAND ANALYSIS OF 500 MB REVEALS A HEIGHT DEPRESSION OVER SOUTH
TEXAS NEAR DEL RIO...ASSOCIATED WITH CYCLONIC CURVATURE SEEN IN
RADAR LOOPS AT 19Z. THIS FEATURE IS EMBEDDED WITHIN A PLUME OF
TROPICAL MOISTURE THAT LIFTED INTO NORTHERN MEXICO AND SOUTH TEXAS
OVER THE PAST FEW DAYS AND IS NOW IN A REGION OF WEAK STEERING
FLOW. THE LARGER SCALE PATTERN RELATED TO A HEALTHY NORTHERN
STREAM TROUGH AND SUB-TROPICAL RIDGING ALONG THE GULF COAST FAVORS
PERSISTENT UPPER DIFLUENCE IN THE VICINITY OF THE MCV...AND ALSO
SUSTAINED LOW LEVEL INFLOW. THIS SITUATION WOULD APPEAR TO BE RIPE
FOR A SIGNIFICANT FLASH FLOOD EVENT...ESPECIALLY GIVEN THE
TENDENCY FOR THIS STYLE OF EVENT TO OCCUR IN THE TEXAS HILL
COUNTRY. THEREFORE...IT WAS NOT TOO SURPRISING WHEN THE CANADIAN
GEM REGIONAL...THE FIRST ARRIVING HI-RES GUIDANCE...DEPICTED A
VERY WET...NEARLY STATIONARY MCV AND LIKELY FLASH FLOOD EVENT OVER
THE SAN ANTONIO / AUSTIN AREA. THIS WAS FOLLOWED UP BY VERY STRONG
AND SIMILAR QPF SIGNALS IN THE NCEP HI-RES WINDOWS AND NSSL WRF.
THE GLOBAL MODELS ALSO HAVE HEAVY RAIN...ESPECIALLY THE ECMWF. THE
HI-RES MODELS AND ECMWF SUPPORT THE NOTION OF A 10-PLUS INCH
RAINFALL EVENT OCCURRING FROM THIS EVENING THROUGH EARLY SUNDAY.
THE QPF SIGNAL IS ORGANIZED...SUGGESTING SOME BREADTH TO THE
EXTREME RAIN TOTALS...PERHAPS AFFECTING MULTIPLE COUNTIES...RATHER
THAN BEING VERY ISOLATED.

BASED ON THE OVERWHELMING MODEL SIGNAL AND HISTORY OF RAPID
HYDROLOGIC RESPONSE IN THIS AREA...WE COORDINATED WITH TEXAS LOCAL
OFFICES TO UPGRADE NOT ONLY TO MODERATE RISK...BUT ALSO TO A SMALL
HIGH RISK AREA CENTERED AROUND SAN ANTONIO / AUSTIN. PLACEMENT OF
THE QPF MAXIMUM IS NOT OF EXTREMELY HIGH CONFIDENCE...BUT WPC
FORECASTERS USING INDEPENDENT METHODS ON THE NIGHT AND DAY SHIFT
CAME UP WITH THE SAME ANSWER FOR LOCATION...WHICH IS SUPPORTED IN
PARTICULAR BY THE WRF-ARW...WHICH TENDS TO PERFORM WELL IN SOUTH
TEXAS. ALSO NOTED THE WRF-ARW AND WRF-NMM QPF SIGNAL INDICATING
NEARLY 150 PERCENT OF THE ONE PERCENT ANNUAL EXCEEDANCE
PROBABILITY OR RECURRENCE INTERVAL RAINFALL. WITH PERHAPS MORE
PEOPLE OUTDOORS / ON THE ROADS ON A SATURDAY NIGHT...FELT IT WAS
PRUDENT TO UPGRADE TO HIGH RISK TO SEND A CLEARLY HEIGHTENED
MESSAGE. THANKS WFO EWX...FWD...CRP...HGX...AND SOUTHERN REGION
FOR COORDINATION.


...ELSEWHERE IN THE LOWER MISSISSIPPI VALLEY AND SOUTHERN PLAINS...

MAINTAINED A MARGINAL TO SLIGHT RISK OVER THROUGH PARTS OF
ARKANSAS / LOUISIANA BASED ON OBSERVATIONAL TRENDS...THE
HRRR...AND THE OVERNIGHT WPC QPF. THOUGH CONVECTION MAY BE LOOSELY
ORGANIZED HERE...IT WILL PRODUCE STRONG SHORT TERM RAIN
RATES...AND FORCING MAY INCREASE NORTHEASTWARD OUT OF THE HILL
COUNTRY BY LATE TONIGHT.


...CENTRAL APPALACHIANS/UPPER OH VALLEY---TN VALLEY...

THE FRONTAL BOUNDARY FROM THE AMPLIFYING TROF OVER THE UPPER MS
VALLEY/UPPER LAKES IS EXPECTED TO BE VERY PROGRESSIVE TO THE EAST
AND SOUTHEAST THROUGH THE LOWER LAKES---OH VALLEY AND TN VALLEY.
WHILE PW VALUES WILL BE ABOVE AVERAGE IN A NARROW BAND ALONG AND
AHEAD OF THE FRONT---2 TO 2.5 STANDARD DEVIATIONS ABOVE THE
MEAN---THE PROGRESSIVE NATURE OF THE BOUNDARY WILL LIMIT POTENTIAL
FOR VERY HEAVY TOTALS. STILL---WELL DEFINED FRONTAL CONVERGENCE IN
THIS HI PW AXIS WILL SUPPORT LOCALLY HEAVY PRECIP TOTALS ALONG AND
AHEAD OF THIS FRONT. A MARGINAL RISK AREA WAS DEPICTED FROM THE
CENTRAL APPALACHIANS/UPPER OH VALLEY REGION INTO THE TN VALLEY
WHERE THERE ARE POCKETS OF RELATIVELY LOWER FFG VALUES IN 1-1.5"
RANGE IN AN HOUR.


...UPPER LAKES...

THE DEEPENING CYCLONE ROTATING THROUGH THE UPPER MS VALLEY/UPPER
LAKES REGION WILL SUPPORT AN ENHANCING COMMA HEAD/DEFORMATION
PRECIPITATION AREA FROM PORTIONS OF THE UPPER MS
VALLEY---NORTHEASTWARD INTO THE UPPER LAKES.  WITH FAIRLY GOOD
MASS FIELD EVOLUTION AMONG THE LATEST MODELS---THERE IS SIMILAR
QPF DISTRIBUTIONS.  HEAVY RAINS LIKELY IN THIS COMMA HEAD
REGION---WITH AREAL AVERAGE 1-2"+ TOTALS FROM NORTHERN WI INTO
EASTERN PORTIONS OF THE UPPER PENINSULA OF MI AND NORTHERN LOWER
PENINSULA--- WITH ISOLATED TOTALS GREATER THAN 3"
POSSIBLE---ESPECIALLY OVER THE CENTRAL U.P. AND FAR NORTHERN WI
WHERE LAKE ENHANCEMENT TO THE PRECIPITATION IS POSSIBLE FROM
STRONG NORTHERLY TO NORTHWESTERLY FLOW OFF OF LAKE SUPERIOR.

BURKE/ORAVEC
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.