Tuesday, August 27, 2013

MESO: Mesoscale Discussion 1783

ACUS11 KWNS 271913
SWOMCD
SPC MCD 271913
MIZ000-WIZ000-272145-

MESOSCALE DISCUSSION 1783
NWS STORM PREDICTION CENTER NORMAN OK
0213 PM CDT TUE AUG 27 2013

AREAS AFFECTED...PORTIONS NRN/ERN WI...LM...EXTREME SRN UPPER
MI...CENTRAL/ERN LOWER MI.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 271913Z - 272145Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...SVR POTENTIAL SHOULD INCREASE DURING NEXT 2-3 HOURS ACROSS
DISCUSSION AREA...WITH LARGEST-PROBABILITY GENESIS REGIONS BEING
CENTRAL-ERN WI AND WRN LOWER MI. INITIAL COMBINATION OF
MULTICELLULAR AND SUPERCELLULAR MODES APPEARS LIKELY...WITH
POTENTIAL FOR EVOLUTION TO LARGER...SEWD TO SSEWD-MOVING CLUSTERS
WITH TIME. LARGE HAIL AND DAMAGING GUSTS ARE POSSIBLE.

DISCUSSION...SFC MESOANALYSIS SHOWS COLD FRONT FROM WEAK LOW INVOF
NRN-CENTRAL UPPER MI...SWWD ACROSS N-CENTRAL/WRN WI TO FRONTAL WAVE
LOCATED BETWEEN MSP-EAU...THEN SWWD ACROSS SRN MN. AS COLD FRONT
PROCEEDS SEWD...IT SHOULD OVERTAKE NRN PORTION OF AGGREGATED
OUTFLOW/DIFFERENTIAL HEATING BOUNDARY. LATTER FEATURE WAS DRAWN
NEAR A LINE FROM CMH...LAN....MBL...AIG...30 N NE EAU...WHERE IT
INTERSECTED COLD FRONT AS OF 19Z. PREFRONTAL BOUNDARY APPEARS
QUASISTATIONARY...AND DENOTES NERN EDGE OF STRONGLY
HEATED'/BETTER-MIXED WARM-SECTOR AIR WITH SFC TEMPS 90S F AND DEW
POINTS LOW-MID 70S. SFC MOIST AXIS WAS DRAWN PARALLEL TO AND ALONG
OR JUST S OF THAT BOUNDARY...EXCEPT OVER N-CENTRAL WI.

TSTMS SO FAR -- ACROSS NRN WI...SRN UPPER MI...NRN LM AND NWRN LOWER
MI -- HAVE BEEN ROOTED IN ELEVATED WAA LAYER WELL N OF BOUNDARY.
HOWEVER...AIR MASS WITHIN 50-60 NM TO ITS NE IS DESTABILIZING ENOUGH
TO SUPPORT SFC-BASED EFFECTIVE INFLOW PARCELS. MODIFIED RAOBS AND
MODEL SOUNDINGS SUGGEST MLCAPE 2000-3000 J/KG ALONG MOIST
AXIS...GRADUALLY DECLINING SWWD INTO WARM SECTOR AND NEWD ACROSS
MODIFIED/OUTFLOW AIR. SFC WINDS NEAR BOUNDARY SHOULD REMAIN RATHER
WEAK...LIMITING BOTH HODOGRAPH SIZE AND STORM-RELATIVE INFLOW.
HOWEVER...GRADIENT FLOW IN MID-UPPER LEVELS IS STG ENOUGH TO YIELD
40-50 KT NWLY EFFECTIVE SHEAR VECTORS...LARGELY PARALLEL TO BOUNDARY
AND SFC MOIST AXIS.

..EDWARDS/THOMPSON.. 08/27/2013

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

ATTN...WFO...DTX...APX...IWX...GRR...MQT...GRB...MKX...ARX...

LAT...LON 44658559 43728438 42988418 42438403 42008423 41798512
41928603 42558634 43178711 43498783 43668908 44098984
45518941 45478753 45058629 44658559

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