Quantitative Precipitation Forecast
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FOUS30 KWBC 251443
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1043 AM EDT SUN SEP 25 2016

...VALID 15Z SUN SEP 25 2016 - 12Z MON SEP 26 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ESE MMCU 85 SW MRF 75 WNW MRF 60 SE MMCS 55 SE MMCS 45 W GDP
50 W LBB 35 SSE PPA 15 SSE WWR 30 ENE AVK WLD 25 ESE CNU
20 ENE COU 20 E MQB 15 N RFD 20 NW SBM 20 WNW LDM 20 NNE GRR
10 SSW IRS 20 SSE LAF 20 ENE FAM 25 NNW MWT 10 WNW 4F4 10 NW LFK
25 NNE BPT 10 S KCMB KVQT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
150 ESE MMCU 115 E MMCU 60 S MRF 10 SW E38 40 W PEQ 30 SW HOB
15 E LBB 50 NNE CDS 25 NW JWG 25 WNW END 15 SW END 15 NNE FSI
DUC PVJ 30 WNW MLC 30 S MKO 20 SW RKR 10 E GVT 20 N 62H
15 SE SSF 25 ESE COT 10 SE LRD 25 E MMMY.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 WSW DRT 45 ESE 6R6 25 NE E29 20 W 6R9 ERV 25 SW UVA
55 NE MMMV.


...TEXAS AND OKLAHOMA....

THE MODERATE RISK AREA IN SOUTHWEST TEXAS EAST OF THE BIG BEND AND
ON THE WESTERN FRINGE OF THE HILL COUNTRY IS NOW REDUCED IN SIZE A
BIT...AND REORIENTED TO ALIGN WITH THE COMBINED COLD POOLS /
EFFECTIVE FRONT IN THIS REGION. IN THE NEAR TERM SUNDAY MORNING
SEE MESOSCALE DISCUSSION 701 FOR DETAILS. LARGE SCALE FORCING WAS
INCREASING OVER THIS REGION WITH GREATER DIFLUENCE ALOFT AND
BACKING AND ACCELERATING OF LOW LEVEL INFLOW. INDIVIDUAL CELL AND
BOUNDARY MOTIONS HAD SLOWED TO YIELD AN ENHANCED POTENTIAL FOR
HEAVY RAINFALL WITHIN AN ENVIRONMENT MARKED BY DEEP TROPICAL
MOISTURE SUPPORTIVE OF VERY HIGH RAIN RATES. WHILE THERE DOES
APPEAR TO BE A FOCUSED EVENT UNFOLDING IN THIS AREA...THE COVERAGE
OF THE EVENT IS SOMEWHAT IN QUESTION...GIVEN THAT THE UPPER LOW IS
PINCHING OFF MUCH FARTHER WEST...AND LOWER TO MIDDLE LEVEL WIND
SPEEDS ARE FORECAST TO DECREASE DURING THE DAY...FROM 20 TO 30
KNOTS EARLY ON...DOWN TO 15 TO 20 KNOTS LATER. DEFINITELY SOME
PROS AND CONS...AS THE PATTERN REMAINS DIFLUENT ALOFT WITH BACKED
INFLOW...BUT AS WIND SPEEDS FALL OFF...SO DOES THE INTENSITY OF
THE DEEP LAYER LIFT...AND DAYTIME MIXING MAY ALLOW FOR A BIT MORE
PROPAGATION OF COLD POOLS TO PUSH THE HEAVY RAINFALL OUT OF ANY
ONE GIVEN SPOT. WHEREVER LOCAL REPEATED RAINS
OCCUR...HOWEVER...MODEL GUIDANCE STILL SUPPORTS SOME HEFTY
TOTALS...ADDITIONAL RAINFALL 4 INCHES OR MORE.

SURROUNDING THE MODERATE RISK IS A RATHER LARGE SLIGHT RISK AREA
WHICH WE EXPANDED ALONG A COUPLE OF AXES POINTED UP INTO THE MID
LEVEL FRONTOGENETICAL ZONE OVER WESTERN OKLAHOMA...AND ALONG THE
EFFECTIVE FRONT INTO NORTHEAST TEXAS AND SOUTHEAST OKLAHOMA.
PARTICULARLY DEEP SATURATION WAS NOTED IN THE 12Z SOUNDINGS FROM
OUN AND FWD. THE SLIGHT RISK AREA TAKES THE SHAPE OF THE 00Z
WRF-ARW QPF...WHILE TAKING INTO ACCOUNT POCKETS OF LOWER FLASH
FLOOD GUIDANCE BASED ON RECENT HEAVY RAINS.

ON THE SOUTHWEST SIDE OF THE RISK AREA...GIVEN THE STRONG EASTERLY
UPSLOPE COMPONENT TO LOW LEVEL WINDS AND ANOMALOUS PW ENVIRONMENT
(2-2.5 STANDARD DEVIATIONS ABOVE NORMAL)...DO NOT FEEL COMFORTABLE
REMOVING THE RISK AREA FROM PORTIONS OF THE PERMIAN BASIN AND
SOUTHEAST NEW MEXICO. ALTHOUGH THE HEAVY RAINFALL OVER THIS AREA
WILL MORE LIKELY FALL OVER A LONGER DURATION...FRONTOGENETICAL
FORCING WILL ACT UPON WHAT IS STILL A VERY MOIST ENVIRONMENT IN
THE POST-FRONTAL REGIME.


...THE OZARKS UP TOWARD LAKE MICHIGAN...

MARGINAL RISK SURROUNDING THE SOUTHERN PLAINS EVENT WAS STRETCHED
UP AHEAD OF THE FRONTAL BOUNDARY ACROSS MISSOURI AND ILLINOIS INTO
THE AREA TO EITHER SIDE OF LAKE MICHIGAN. FLASH FLOOD GUIDANCE IS
A BIT LOWER OVER SOUTHEAST WISCONSIN...BUT OF MORE CONCERN WAS THE
METEOROLOGICAL SETUP. A NARROW PLUME OF PRECIPITABLE WATER VALUES
NEARING 2 INCHES...WELL ABOVE CLIMATOLOGICAL NORMS...WILL BE SWEPT
UP THROUGH THIS REGION AT A FAVORABLE TIME OF DAY...21-03Z...AND
MAY CONTRIBUTE TO VERY HEAVY SHORT TERM RAIN RATES...ESPECIALLY
OVER PARTS OF WI/IL/IN...WHERE A LOCAL MAXIMUM OF CAPE SHOULD FORM
NEAR THE RETREATING WARM FRONT. ALTHOUGH THE HRRR HOURLY QPF IS
MUCH LESS...SOME OF THE NCEP HI-RES WINDOWS PRODUCE GREATER THAN
ONE INCH HOURLY RATES...AND NEIGHBORHOOD PROBABILITIES OF
FFG-EXCEEDANCE FROM THE SSEO SPIKE AT 30 PERCENT THIS AFTERNOON IN
SOUTHEAST WISCONSIN. PROGRESSIVE CELL MOTIONS OF 20 KNOTS OR
SO...SHOULD LESSEN THE OVERALL POTENTIAL...BUT ISOLATED INSTANCES
OF FLASH FLOODING ARE POSSIBLE.

BURKE/HURLEY
$$





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