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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1431Z Sep 29, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1031 AM EDT MON SEP 29 2014

...VALID 15Z MON SEP 29 2014 - 12Z TUE SEP 30 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
PFN VDI 25 ESE OGB 30 SSW MYR 65 ESE CHS 45 ENE SSI 25 ENE DAB
35 ENE VRB 10 N PBI 50 WSW PBI 15 SSE ISM 10 WNW VVG 20 SE CTY
25 SW 40J 15 SW AAF PFN.


...CENTRAL/PART OF THE NORTHERN HIGH PLAINS...

THE RATHER STRONG/DEEP CLOSED H5 LOW NOW OVER THE CENTRAL GREAT
BASIN IS FORECAST SIMILARLY BY ALL OF THE MODEL GUIDANCE TO LIFT
OUT AND OPEN UP INTO A NEGATIVE TILT H5 TROF THAT REACHES INTO THE
CENTRAL AND NORTHERN HIGH PLAINS BY THE END OF THE PERIOD.  THIS
MORE PROGRESSIVE/LIFTING OUT PROCESS WILL BE ACCOMPLISHED BY THE
STRONG S/WV WHICH IS NOW DROPPING INTO THE BACKSIDE OF THE CLOSED
LOW OVER CENTRAL CA..WITH THIS S/WV ROTATING INTO THE
CENTRAL/SOUTHERN ROCKIES BY MONDAY EVENING AND THEN LIFTING MORE
NORTHWARD THRU THE CENTRAL PLAINS AND INTO PARTS OF THE NORTHERN
PLAINS IN NEGATIVE TILT FASHION MONDAY NIGHT.  AHEAD OF THIS
STRONG NEGATIVE TILT S/WV..THE SOUTHEASTERLY LOW LEVEL JET WILL
REALLY STRENGTHEN INTO THE CENTRAL AND NORTHERN HIGH PLAINS MONDAY
NIGHT BRINGING IN HIGHER PWS FROM THE SOUTHEAST..WHILE LARGE SCALE
LIFT WILL REALLY BE ENHANCED OVER THE SAME REGION UNDER AN
INCREASINGLY FAVORABLE UPPER DIFFLUENT PATTERN.  THIS INCREASE IN
MOISTURE/STRENGTHENING LARGE SCALE LIFT REGIME WILL LEAD TO A
SUBSEQUENT INCREASE IN RAINS ON MONDAY NIGHT FROM THE CO FOOTHILLS
NORTHWARD THRU THE CENTRAL AND NORTHERN HIGH PLAINS..WITH AN AXIS
OF HEAVY RAINS LIKELY AND EVEN MORE ENHANCED RAINS LIKELY VICINITY
OF THE BLACK HILLS WHERE LOW LEVEL UPSLOPE FLOW COMES INTO PLAY. 
FOR THE MOST PART THE MODEL QPFS ARE IN DECENT AGREEMENT HERE AND
STAYED CLOSE TO THEIR SOLUTION.  EXPECT AT LEAST SOME 1-2 INCH
AREAL AVERAGE RAINS FROM WESTERN NE NORTHWARD THRU WESTERN SD AND
INTO SOUTHWESTERN ND AS WELL AS EASTERN PARTS OF WY AND
SOUTHEASTERN MT..WITH SOME ISOLATED 3+ INCH AMOUNTS
POSSIBLE..ESPECIALLY VICINITY OF THE BLACK HILLS.  THESE RAINFALL
AMOUNTS MAY CAUSE SOME LOCAL RUNOFF PROBLEMS.


...SOUTHEAST...

NORTHWARD EXPANSION OF THE HEAVIER RAIN CORES ACROSS THE SOUTHEAST
THIS MORNING PER THE CURRENT RADAR LOOPS IS SOMEWHAT CONTRADICTORY
FROM THE PREVIOUS RUNS OF SOME OF THE 00/06Z HIGH-RES GUIDANCE.
OBSERVED RAINFALL REPORTS COMING IN (TOTALS OF 2.25-4.25+ INCHES
ALONG THE COAST NEAR CHARLESTON SC PER WFO CHS) ARE GENERALLY
HIGHER THAN THE RADAR ESTIMATES...INDICATIVE OF THE EFFICIENT WARM
RAIN PROCESSES WITH THE DEEP WARM CLOUD LAYER (WET BULB ZERO
HEIGHTS ~14000 FT OR HIGHER) AND HIGH PWS (AOA 2.25 INCHES PER THE
12Z KCHS RAOB AND LATEST GPS DATA). CONTINUE TO EXPECT SUSTAINED
DYNAMICAL SUPPORT (UPPER LEVEL DIVERGENCE AND MORE FOCUSED
SOUTHERLY LOW LEVEL MOISTURE CONVERGENCE) AHEAD OF THE SHORTWAVE
TROUGH AND TO MAINTAIN THE WIDESPREAD WARM TOPPED CONVECTION. THE
WIDESPREAD CLOUD COVER/LACK OF DIFFERENTIAL HEATING AND WEAK/MOIST
ADIABATIC LAPSE RATES ALOFT WILL TEND TO LIMIT THE RAINFALL RATES
FOR MOST...HOWEVER HIGHER MUCAPES (1000-2000 J/KG) ALONG AND SOUTH
OF THE SFC FRONTAL BNDRY CURRENTLY ACROSS NRN FL WILL ENHANCE THE
EXCESSIVE RAINFALL POTENTIAL ACROSS NORTHERN FL INTO EASTERN
PORTIONS OF THE FL PENINSULA...ESPECIALLY GIVEN THE ENHANCED
CONVERGENCE VIA THE GULF/SEA BREEZE COMPONENT.

HURLEY