Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 171458
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EDT WED AUG 17 2016

...VALID 15Z WED AUG 17 2016 - 12Z THU AUG 18 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
135 E MMCU 15 SSW FST 10 NNW ABI 15 WSW GYI 10 NW M89
40 ESE PBF 30 SE GLH 15 WSW LCH 10 SW BYY 15 NNW ALI 30 ENE MMMY.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW BKL JXN 15 E MBL 20 NW PZQ 10 SE CWBE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 E MQI 10 E FVX 20 WNW ROA 15 SW LNP 15 WSW EKQ 30 SSE OWB
20 E HNB 15 NW ILN 15 NNW ILN 10 WSW BTP 15 E ACY 120 ESE ACY.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
120 NW MMMV 20 NNE 6R6 10 NNW SJT 10 SSE GDJ 20 WSW 3T1
35 ENE TXK 35 E ELD 10 W MLU 10 NNE LFK 20 ENE HDO 15 S UVA
30 NE MMMV.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 ENE FFA FYJ 10 S LKU SHD W99 10 W MRB MTN 10 S RJD
25 WNW WAL 15 WSW MFV.


...TEXAS/LA/AR...

STRONGLY POSITIVE MOISTURE ANOMALIES WILL REMAIN IN PLACE ACROSS
ACROSS CENTRAL TO NORTHEAST TX IN TANDEM WITH THE MID-UPPER LEVEL
TROUGH. THE 00Z NAM SHOWS PRECIPITABLE WATER (PW) ANOMALIES OF 2-3
STD DEVIATIONS ABOVE NORMAL IN THE RIO GRANDE VALLEY OF CENTRAL
TEXAS. A REMNANT STATIONARY FRONT ACROSS THE REGION WILL AID
LIFT...WITH FURTHER SUPPORT FROM UPPER DIVERGENCE MAXIMA ACROSS
MUCH OF CENTRAL TO NORTHEAST TX/ARKLATEX. THE LIFT COMBINED WITH
ABOVE NORMAL MOISTURE SUPPORTS WIDESPREAD SHOWERS WITH LOCALLY
HEAVY RAIN. DEEP LAYER WINDS ARE FORECAST TO BE LIGHT OUT OF THE
SOUTH TO SOUTHWEST...SUPPORTING SLOW MOVING CELLS. LONGER DURATION
RAINS MAY LEAD TO LOCALIZED FLOODING AFFECTING CENTRAL/SOUTHERN
TEXAS/ARKLATEX. THE LAST COUPLE OF DAYS WIDESPREAD SHOWERS HAVE
DEVELOPED EAST OF THE CYCLONIC SHEAR AXIS IN THE LOW LEVEL INFLOW
REGION OF HIGHER
PW VALUES...AND MANUAL PROGS FOLLOWED THIS IDEA AGAIN...SUPPORTED
BY LOCALIZED MAXIMA IN THE HIGH RES WRF ARW/NSSL WRF AND CANADIAN
REGIONAL GEM.


...MID ATLANTIC AND CENTRAL APPALACHIANS...

AT 15Z WE INTRODUCED A SLIGHT RISK OVER THE MID ATLANTIC AFTER
MAKING SOME ADJUSTMENTS TO THE EXPECTED QPF AND THROUGH
COORDINATION WITH LOCAL OFFICES. IN THE 18Z QPF RELEASE WE WILL BE
NUDGING THE AXIS OF HEAVIEST RAIN NORTHWARD WHERE THE MAJORITY OF
HI-RES GUIDANCE HAS IT FROM NOVA THROUGH THE DC AREA AND ANAPOLIS
TO THE EASTERN SHORT OF MD. A SECONDARY MAXIMUM...HOWEVER...IS
EXPECTED DOWN TOWARD RICHMOND...WHILE A THIRD LOCAL MAXIMUM IS
EXPECTED OVER WEST VIRGINIA. THE STRONG WAVE EXITING NEW ENGLAND
HAD VEERED WINDS SUCH THAT A TROUGH AXIS AND CAPE AXIS WILL BECOME
ORIENTED FROM CENTRAL VA UP THROUGH EASTERN MD TODAY. SUFFICIENT
MOISTURE AND INSTABILITY EXISTS BACK WEST OF THE TROUGH
AXIS...HOWEVER...FOR THUNDERSTORMS TO ROLL OFF THE HIGHER TERRAIN
AND MERGE WITH ANY ACTIVITY OCCURRING DOWN IN THE COASTAL PLAIN.
DEEP WESTERLY FLOW SHOULD YIELD FAIRLY QUICK INDIVIDUAL STORM
MOTIONS...BUT THE PROSPECT FOR CELL MERGERS IN A VERY MOIST
ENVIRONMENT RAISES THE POSSIBILITY OF ISOLATED INTENSE SHORT TERM
RAIN RATES. WHAT PUSHES THIS BEYOND MARGINAL AND INTO THE SLIGHT
RISK CATEGORY IS THE PERSISTENT SYNOPTIC LIFT THAT WILL ACCOMPANY
A SHORTWAVE ARRIVING THIS EVENING...SUCH THAT MULTIPLE ROUNDS OF
STORMS MAY AFFECT SOME AREAS...AS INDICATED BY ENSEMBLE
PROBABILISTIC QPF OUTPUT WHICH SHOWS SOME NON-DIURNAL
TRENDS...PEAKING AROUND 3-6Z. FLASH FLOOD GUIDANCE VALUES ARE ALSO
RELATIVELY LOWER WITHIN THE SLIGHT RISK AREA...AND ALSO BACK
ACROSS WEST VIRGINIA...ALTHOUGH RESIDENCE TIME OF CONVECTION
SHOULD BE LESS THERE.


...LOWER MICHIGAN...

THOUGH DEEP TROPICAL MOISTURE HAD BEEN SHUNTED OFF TO THE EAST...A
SECONDARY AXIS OF ENHANCED PRECIPITABLE WATER VALUES WILL
ACCOMPANY A SHORTWAVE TROUGH CROSSING THE LOWER PENINSULA TODAY.
SHORT TERM RAIN RATES WERE ALREADY ABOVE 1 INCH PER HOUR THIS
MORNING PER RADAR ESTIMATES. FLASH FLOOD GUIDANCE COULD BE
EXCEEDED LOCALLY...ESPECIALLY IN EASTERN LOWER MICHIGAN WHERE VERY
HEAVY RAIN HAD FALLEN IN RECENT DAYS. THE MODEL QPF SIGNAL IS NOT
PARTICULARLY ROBUST HERE...HOWEVER...WITH MOST HI-RES GUIDANCE
SUGGESTING ONLY ISOLATED TOTALS ABOVE 2 INCHES FOR THE EVENT TODAY.

BURKE/PETERSEN
$$





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