EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
223 PM EDT SUN MAY 19 2013

...VALID 18Z SUN MAY 19 2013 - 00Z TUE MAY 21 2013...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 E KD50 15 ENE CWNK 20 W CWCH CYQT 35 NNW CMX 15 W ARV
15 ESE EAU 20 NNE CCY 10 SSE MCW KACQ 15 NW MIC 20 SSE GPZ
25 SSE VWU 10 SSE FSE 10 NNW FFM 25 S KGWR 45 W K2D5 25 SW K46D
35 SW K5H4 35 ESE DIK HEI 50 N RCA 30 ESE IKA 30 NE GCC
10 ESE BYG 30 WSW PIN 40 S BIL 10 SSW BIL 55 ENE BIL 25 SSW MLS
35 SSE OLF 15 E KD50.


...SERN MT/NERN WY/NWRN SD/MUCH OF ND INTO NRN WI AND NRN/ERN MN...

ONCE AGAIN MODIFIED THE PREVIOUS EXCESSIVE RAINFALL SLIGHT AREA TO
INCLUDE PARTS OF MN AND NRN WI THROUGH 00Z/21. THE MAIN FOCUS
CONTINUES TO BE THE MDT TO HVY SYNOPTIC SCALE RAINS WHICH WILL
PERSIST FROM SERN MT/NERN WY TO NWRN SD AND WRN/NRN ND... AS MOIST
INFLOW CONTINUES TO FUEL DEFORMATION/DYNAMIC COOLING RAINS ON THE
BACKSIDE OF THE INTENSIFYING LOW PRESSURE SYSTEM OVER THE UPPER
MIDWEST. 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 UPSLOPE/OROGRAPHIC ENHANCED RAIN IN THE BURN
AREAS. AM A BIT WORRIED THOUGH THAT ALL OF THE OPERATIONAL MODELS
PERHAPS ARE OVERDONE ON THE QPF AMOUNTS FOR THE ENTIRE AREA...
DESPITE PLENTIFUL LL MOISTURE OVERRUNNING INTO THE COOLER SECTOR
AND PROLONGED EVENT... 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. MEANWHILE OUT AHEAD OF THE AREA OF LOW
PRESSURE... DEEP SRLY FLOW AND WARM SECTOR WILL BEGIN TO SPREAD
NORTH INTO MN/WI... WHERE DEVELOPING CONVECTION OVER NE/IA
ASSOCIATED WITH MID-LEVEL VORT/DYING MCV COULD TRIGGER HEAVIER
RAINFALL OVER THE NEXT DAY. THIS AXIS THE GUIDANCE SOMEWHAT
PINPOINTS IS FROM NERN IA/SERN MN NORTH AND EAST INTO NRN WI/NERN
MN.

...CENTRAL PLAINS...

FROM SERN KS/ERN OK INTO WRN/CENTRAL MO A SEE TEXT AREA WILL
CONTINUED TO BE CARRIED IN ANTICIPATION OF CONVECTIVE HEAVY RAIN
ELEMENTS LATER THIS EVENING INTO TMRW. 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 EVENING... ORGANIZES AND THEN
PROPAGATES DOWNSTREAM REMAINS HIGHLY UNCERTAIN. THE HIGHLY
VOLATILE AND MOST LIKELY AREA FOR ANY EXCESSIVE RAINS WILL BE
ACROSS SERN KS/NERN OK INTO WRN MO AND THE ECMWF/GFS AGREE ON THIS
THINKING. THE FFG IS NOT SERIOUSLY LOW BUT WILL STICK WITH THE SEE
TEXT.

...NRN GA/ERN TN TO SC AND WRN/CENTRAL 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 HAS DEVELOPED AND BEGAN TRAINING AND
PROPAGATE SOUTH AND EAST TO PARTIALLY 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 AT BEST
AND THE FOCUS LATER TODAY INTO TMRW APPEARS BE SETTING UP OVER
SC/CENTRAL NC... AS SMALL POCKET OF COOLER AIR ALOFT WITH DAYTIME
HEATING INTERACTS WITH POOLING PW MAX FOR SLOW MOVING CONVECTIVE
RAINFALL.

MUSHER