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FOUS30 KWBC 191418
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1018 AM EDT SUN MAY 19 2013

...VALID 15Z SUN MAY 19 2013 - 12Z MON MAY 20 2013...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W IDV 30 N GEY 15 SW BIL 40 E 3HT 45 ESE LWT 65 NNE BIL
65 W MLS 35 SSW MLS 30 E MLS 15 SSW ISN 30 NNW K06D 20 E CWGN
15 SE CKN 25 SW FAR 30 W JMS 25 SSW KY19 25 SSW D07 20 W RCA
15 SE GCC 30 NNE TMH 20 W IDV.


...SERN MT/NERN WY TO NWRN SD/MUCH OF ND...

NARROWED THE PREVIOUS EXCESSIVE RAINFALL SLIGHT AREA TO REMOVE
MUCH OF SD AND MN AND FOCUS ON MDT TO HVY RAINS WHICH WILL LIKELY
PERSIST FROM SERN MT/NERN WY TO NWRN SD/MUCH OF ND. THE SPECIFIC
REASONING FOR REMOVING SD/MN IS TWO-FOLD... SYNOPTIC SCALE PRECIP
SHIELD HAS LIFTED OUT THIS MORNING TO EVENTUALLY BE REPLACED BY
STRONG DESTABILIZATION AND LIKELY CONVECTIVE ELEMENT THIS
AFTN/EVENING BUT THE GUIDANCE REALLY VARIES ON THE EXACT LOCATION
OF THIS LIKELY SW TO NE PROPAGATING PROGRESSIVE CONVECTION WITH
ELEMENTS OF HEAVIER RAINFALL. THUS WENT AHEAD AND DECREASED THE
SLIGHT TO A SEE TEXT FOR THE UNCERTAINTY OF CONVECTIVE DEVELOPMENT
AND EXPECTED PROGRESSIVE FASHION OF THIS TSTRM ACTIVITY. MEANWHILE
IN THE COLD SECTOR... MDT TO HVY NON-CONVECTIVE RAINFALL IS
EXPECTED TO PERSIST... AS MOIST INFLOW CONTINUES TO FUEL
DEFORMATION/DYNAMIC COOLING RAINS ACROSS NERN ND SWWRD INTO SWRN
ND/NWRN SD OR ON THE BACKSIDE OF THE INTENSIFYING LOW PRESSURE
SYSTEM. ALSO... 1 HRLY FFG IS MUCH LOWER THROUGH THIS CORRIDOR
BACK INTO SERN MT/NERN WY... WHERE CYCLONIC FLOW SHOULD FUEL SOME
INCREASING VERTICAL LIFT FOR THE UPSLOPE/OROGRAPHIC BURN AREAS. AM
A BIT WORRIED THOUGH THAT ALL OF THE OPERATIONAL MODELS PERHAPS
ARE OVERDONE ON THE QPF AMOUNTS FOR THE ENTIRE AREA THROUGH
12Z/20... DESPITE PLENTIFUL LL MOISTURE OVERRUNNING INTO THE
COOLER SECTOR... THE AIR MASS IS NOT REAL UNSTABLE AND LATER
CONVECTION OUT OVER THE PLAINS COULD PROHIBIT THESE 2 TO 3 INCH
NUMBERS BY THE MODELS.

...CENTRAL PLAINS TO UPR MS VLY...

FROM ERN KS/WRN MO INTO ERN SD AND MUCH OF MN TWO SEE TEXT AREAS
WILL BE ISSUED FOR THE LATER DEVELOPMENT THIS AFTN/EVENING OF
CONVECTIVE HEAVY RAIN ELEMENTS. THE LARGE SCALE UPPER TROUGH
EMERGING FROM THE WEST WITH AN ANOMALOUS SURFACE COLD FRONTAL
BOUNDARY WILL INTERACT WITH MOIST AIR MASS AND INCREASING SRLY
850MB FLOW FOR POSSIBLE AREAS OF CONVECTION AND HEAVY RAINFALL. A
POTENT UPPER JET WILL SLICE INTO THE CENTRAL PLAINS LATER THIS
EVENING AND FAVORABLE LEFT EXIT REGION DYNAMICS SHOULD FUEL THE
CONVECTION/HVY RAINFALL. HOWEVER... EXACTLY HOW/WHERE THIS
ACTIVITY DEVELOPS THIS AFTN... ORGANIZES AND THEN PROPAGATES
DOWNSTREAM REMAINS HIGHLY UNCERTAIN. THE LOWER FFG IS FROM SERN
SD/NERN NE INTO IA/SRN MI BUT THESE VALUES ARE ABOUT AN INCH TO
INCH AND A HALF WITHIN AN HR... WHICH IS POSSIBLE BUT UNLIKELY TO
BE WIDESPREAD AND COVER THE ENTIRE REGION. THE OTHER HIGHLY
VOLATILE AREA WILL BE ACROSS SERN KS/NERN OK INTO WRN MO... WHERE
MORNING CONVECTION WILL LIKELY LEAVE LEFTOVER OUTFLOW BOUNDARIES
FOR MORE ORGANIZED AREAS OF HEAVIER RAINFALL.

...NRN GA/ERN TN TO UPSTATE SC/WRN NC...

THE TRAPPED MID-LEVEL LOW NEAR THE SRN APPALACHIANS FUELED A HEAVY
RAINFALL COMPLEX OVERNIGHT ACROSS NRN/NERN GA WITHIN INCREASING
WARM ADVECTION REGIME. AS THIS ACTIVITY HAS WEAKENED... MORE
UPSTREAM DEVELOPMENT OVER ERN TN/NWRN GA NEAR THE EDGE OF A MOIST
DECAYING DEWPOINT BOUNDARY SEEMS POISED O POSSIBLY PROPAGATE SOUTH
AND EAST AND CLIP THE AREAS IMPACTED OVERNIGHT IN GA. THE GUIDANCE
INCLUDING THE HI-RES OUTPUT HAS HANDLED THIS ACTIVITY OVER THE
PAST 6 TO 12 HRS MARGINALLY AND MOST FOCUS LATER TODAY ACROSS
UPSTATE SC/WRN NC FOR HEAVIER RAINS... AS SMALL POCKET OF COOLER
AIR ALOFT WITH DAYTIME HEATING INTERACTS WITH POOLING PW MAX FOR
SLOW MOVING CONVECTIVE RAINFALL.

MUSHER
$$