Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 112146
QPFERD

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

...VALID 21Z THU SEP 11 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
30 ENE T82 15 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 15 NNW CQC 45 E LVS 55 SE LVS 25 WSW AMA
25 SE AMA 35 WSW CDS 60 NNE SNK RPH 15 E AQR 15 NE M89 20 N ELD
15 SSE JSO 30 ENE T82.

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 THE FOCUS FOR CONVECTION ACROSS THE
ARKLATEX AND SOUTHEAST NM THIS PERIOD.  INITIALLY, A BAND OF
SCATTERED THUNDERSTORMS IS SLOW TO MOVE ACROSS THE REGION, THOUGH
IT IS REMAINING WITHIN THE SINGLE CELL/PULSE MODE DUE TO MINIMAL
LOW-LEVEL INFLOW/0-3 KM SHEAR.  CONVECTION ALONG THE BOUNDARY IS
INITIALLY SURFACE-BASED, BUT IS EXPECTED TO BECOME MORE ELEVATED
CLOSE TO THE 850 HPA SLICE OF THE FRONT.  A BRIEF SHOT LOW-LEVEL
INFLOW SHOULD INCREASE THE CONVECTION CLOSE TO THE ARKLATEX
TONIGHT BEFORE INFLOW AND INSTABILITY WANES.  RECENT RAP GUIDANCE
SUGGESTS THAT 1000+ J/KG CAPE VALUES SLOWLY SETTLE SOUTHWARD
OVERNIGHT, RETREATING FAR ENOUGH AWAY FROM THE BOUNDARY BY 07Z TO
INDICATE THAT TO BE THE HORIZON OF ANY EXCESSIVE RAINFALL/FLASH
FLOOD THREAT NEAR THE ARKLATEX.

THE FOCUS SHIFTS INCREASINGLY TOWARDS WESTERN TX AND SOUTHEAST NM
WHERE STRONG UPSLOPE FLOW OF UP TO 40 KTS COMBINES WITH GOOD
DIFFLUENCE ALOFT BEHIND AN ADVANCING BLUE NORTHER/RAPIDLY MOVING
SHALLOW COLD POOL, WHICH 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.  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.  THE MESOSCALE GUIDANCE IS NEARLY UNANIMOUS IN ADVERTISING
LOCAL AMOUNTS OF 5-8" IN SOUTHEAST NM.  USING THIS AS A GUIDE, THE
FLASH FLOOD/EXCESSIVE RAINFALL THREAT FOR THIS WESTERN REGION
SHOULD PERSIST WELL INTO FRIDAY.


SOUTH 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.  PER CONCEPTUAL MODELS, LOCAL
AMOUNTS OF 3-5" ARE ANTICIPATED, WHICH WOULD APPROACH THE HIGH
FLASH FLOOD GUIDANCE ACROSS THE REGION.

ROTH
$$





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