MESO: Mesoscale Discussion 1816

ACUS11 KWNS 312001
SWOMCD
SPC MCD 312001
IAZ000-NEZ000-SDZ000-312200-

MESOSCALE DISCUSSION 1816
NWS STORM PREDICTION CENTER NORMAN OK
0301 PM CDT SAT AUG 31 2013

AREAS AFFECTED...PORTIONS CENTRAL/ERN NEB...S-CENTRAL/SERN SD...WRN
IA.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 312001Z - 312200Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...INITIALLY CONDITIONAL SVR POTENTIAL SHOULD BECOME BETTER
FOCUSED AND DEFINED OVER MUCH OF DISCUSSION AREA DURING NEXT COUPLE
OF HOURS...AND WW MAY BE REQUIRED. DAMAGING GUSTS AND LARGE HAIL
WOULD BE PRIMARY CONCERNS.

DISCUSSION...SFC ANALYSIS SHOWS COLD FRONT FROM CENTRAL SD SWWD
ACROSS SANDHILLS NEAR VTN TO NEAR AKO. FRONT SHOULD PROCEED SLOWLY
ESEWD OVER N-CENTRAL/SWRN NEB THROUGH REMAINDER AFTN. AHEAD OF
FRONT...SUBTLE CONFLUENCE AXES WERE DRAWN NEAR HLC-ODX-ONL AND
ITR-LBF-HON LINES. FCST SOUNDINGS STILL SHOW 50-150 J/KG MLCINH
OVER MOST OF THIS AREA...BUT CONTINUED STG SFC HEATING SHOULD ERODE
THAT OVER NEXT 2-3 HOURS. FRONT AND CONFLUENCE LINES ARE POTENTIAL
FOCI FOR INITIATION. ALSO...INITIALLY ELEVATED/MIDLEVEL-ROOTED
CONVECTION MOVING ESEWD OVER N-CENTRAL NEB MAY BECOME SFC-BASED
WHILE MOVING EWD TOWARD MO RIVER VALLEY MOIST AXIS. MOISTURE PLUME
OVER ERN NEB IS CHARACTERIZED BY UPPER 60S TO 70S F SFC DEW
POINTS...COMBINING WITH SFC HEATING AND STEEP LAPSE RATES ALOFT TO
YIELD MLCAPE NEAR 3000 J/KG.

DEEP SHEAR WILL BE MRGL FOR SUPERCELLS BUT FAVORABLE FOR ORGANIZED
MULTICELLS AND QUASI-LINEAR SEGMENTS...WITH 30-40 KT EFFECTIVE SHEAR
MAGNITUDES. LIMITING FACTOR FOR BOTH SHEAR AND CONVERGENCE WILL BE
LACK OF MORE ROBUST SFC FLOW...WITH WINDS OBSERVED FROM CALM TO 10
KT ACROSS MUCH OF THIS AREA. FLOW MAY INCREASE SOMEWHAT THROUGH
REMAINDER AFTN AS HEATING/MIXING CONTINUE...AND AS ISALLOBARIC
FORCING INCREASES N OF AREA DUE TO STG SHORTWAVE TROUGH NEAR
CANADIAN BORDER.

..EDWARDS/GOSS.. 08/31/2013

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...DMX...FSD...OAX...ABR...GID...LBF...UNR...

LAT...LON 42790027 44119975 43639853 43729738 43419659 43489500
42039543 41199653 40189708 40809907 41120112 42790027

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