Quantitative Precipitation Forecast
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FOUS30 KWBC 120118
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
917 PM EDT THU SEP 11 2014

...VALID 03Z FRI SEP 12 2014 - 00Z SAT SEP 13 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W SPD 25 ESE AMA 10 E ABI 35 NNW 6R9 25 NNW T82 15 NE ECU
35 WNW ECU 6R6 25 SE E38 45 SSW MRF 75 SSW GDP 15 NE ELP
10 S HMN 25 ENE LRU 35 E TCS 30 ENE TCS 30 NE TCS 50 NE TCS
30 S ABQ 20 NNW 4MY TAD 15 W SPD.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE GDP 15 WNW GDP 40 ESE ALM 20 SSE ALM 10 W SRR 20 NNE SRR
50 ENE 4CR 60 WSW CVS 35 NE ROW 50 E ROW 30 NNE HOB 30 NNE INK
15 NNE PEQ 35 W PEQ 20 SSE GDP.


ARKLATEX/NM
~~~~~~~~~~~
A FRONTAL BOUNDARY SHOULD BE RESPONSIBLE FOR CONVECTION ACROSS
WESTERN TX AND SOUTHEAST NM THIS PERIOD.  WITH TIME, STRONG
UPSLOPE FLOW OF UP TO 40 KTS COMBINES WITH GOOD DIFFLUENCE ALOFT
BEHIND AN ADVANCING BLUE NORTHER/RAPIDLY MOVING SHALLOW COLD FRONT
TO SQUEEZES OUT THE AVAILABLE MOISTURE IN THE FORM OF HEAVY
RAINFALL.  PRECIPITABLE WATER VALUES ARE EXPECTED TO BE ~1.75",
WHICH IS CLOSE TO TWO SIGMAS ABOVE AVERAGE, OR NEAR THE 90TH
PERCENTILE FOR MID-SEPTEMBER, AND SUPPORTS HOURLY RAIN RATES UP TO
2".  RECENT RAP GUIDANCE SHOWS A SLOW DRAW DOWN TO THE AVAILABLE
CAPE/INSTABILITY IN THIS AREA.  USUALLY IN AN UPSLOPE REGIME WITH
PW VALUES THIS HIGH, 500 J/KG CAN BE ENOUGH INSTABILITY TO
MAINTAIN A FLASH FLOOD THREAT.  USING THIS AS A GUIDE, THE FLASH
FLOOD/EXCESSIVE RAINFALL THREAT FOR THIS WESTERN REGION SHOULD
PERSIST WELL INTO FRIDAY.  THE MESOSCALE GUIDANCE IS NEARLY
UNANIMOUS IN ADVERTISING 5-8" LOCAL MAXIMA ACROSS SOUTHEAST NM.
THE NORTHERN EDGE OF THE EXCESSIVE AREA WAS EXTENDED NORTHWARD TO
ACCOUNT FOR TRAINING/STATIONARY STORMS CURRENTLY ACROSS NORTHERN
NM AND SOUTHWEST CO.


SOUTHERN FL
~~~~~~~~~~~
ACROSS FL, A COMPACT TROPICAL DISTURBANCE IS FORECAST TO CROSS THE
SOUTHERN PORTION OF THE STATE SOUTH OF LAKE OKEECHOBEE.
PRECIPITABLE WATER VALUES OF 2" ARE EXPECTED HERE, IMPLYING HOURLY
RAIN RATES UP TO 2.5" ARE POSSIBLE.  USING CONCEPTUAL MODELS AS A
GUIDE, LOCAL AMOUNTS OF 3-5" ARE ANTICIPATED, WHICH WOULD APPROACH
THE HIGH FLASH FLOOD GUIDANCE ACROSS THE REGION.


SOUTHEAST VA/EASTERN NC/EASTERN SC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A FRONTAL ZONE SAGS INTO THE AREA THIS PERIOD, BRINGING
PRECIPITABLE WATER VALUES OF 2-2.25" INTO THE REGION, WHICH
SUPPORTS HOURLY RAIN RATES UP TO 2.5".  FLASH FLOOD GUIDANCE IN A
FEW SPOTS REMAIN LOW FROM THE HEAVY RAIN EVENT SEPTEMBER 7-8,
WHICH IS A PARTICULAR CAUSE FOR CONCERN IN THE NORFOLK VA AREA,
THOUGH THUNDERSTORMS SHOULD MIGRATE FAST ENOUGH THROUGH THAT
REGION TONIGHT TO MINIMIZE THE FLASH FLOOD/EXCESSIVE RAINFALL
RISK.  THE GUIDANCE FORECASTS 850 HPA INFLOW OF ~10 KTS INTO THE
REGION ACROSS THE CAROLINAS, WHICH IMPLIES A SINGLE CELL/PULSE
THUNDERSTORM ENVIRONMENT.  CORFIDI VECTORS ARE LIGHT ACROSS THE
REGION, IMPLYING LITTLE CELL MOTION EVEN TO THOSE CELLS WHICH TRY
TO ORGANIZE.  IT IS POSSIBLE THAT FLASH FLOODING COULD OCCUR IN
THIS REGION.

ROTH
$$





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