SWOMCD
SPC MCD 272000
MIZ000-WIZ000-MNZ000-272200-
MESOSCALE DISCUSSION 2037
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT SUN SEP 27 2009
AREAS AFFECTED...PORTIONS NRN WI...WRN LS...ARROWHEAD REGION OF NERN
MN...WRN UPPER PENINSULA OF MI.
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 272000Z - 272200Z
TSTM COVERAGE/INTENSITY EXPECTED TO INCREASE FROM SWRN SHORE LS
ACROSS NRN WI AND ADJOINING AREAS OF WRN UPPER MI THROUGH LATE
AFTERNOON. MAIN CONCERN WILL BE OCCASIONAL HAIL.
SFC MESOANALYSIS SHOWS DIFFUSE SFC COLD FRONT...ACCOMPANIED BY NWLY
WIND SHIFT AND GRADUAL DECLINE OF THETAE....FROM WRN LS JUST E
DLH...SSWWD ACROSS NWRN WI BETWEEN MSP-EAU...TO NEAR DSM. FRONT
SHOULD CONTINUE TO MOVE SEWD ACROSS REGION. LIFTED PARCELS
ALONG/AHEAD OF FRONT OVER NRN WI APPEAR SFC-BASED NOW...NEAR
RELATIVE SFC THERMAL MAX AT PBH...AND MLCINH IS WEAKENING FARTHER
EWD TOWARD WRN UPPER MI. SFC HEATING BEHIND FRONT HAS OFFSET CAA
ENOUGH TO RENDER UNCAPPED AIR MASS...BENEATH COLD AIR ALOFT. THIS
WILL SUPPORT DEVELOPMENT OF POSTFRONTAL TSTMS AS WELL...ALTHOUGH
MORE INTENSE CONVECTION SHOULD REMAIN ALONG/AHEAD OF FRONT WHERE
BOUNDARY LAYER MOISTURE IS MAXIMIZED. DEEP CONVECTION MOVING ESEWD
AWAY FROM DLH AREA -- AS WELL AS TCU EVIDENT ON 1930Z VIS IMAGERY AS
FAR S AS BARRON COUNTY WI -- WILL MOVE THROUGH ENVIRONMENT
CHARACTERIZED BY 35-45 KT EFFECTIVE SHEAR. SHEAR IS EXPECTED TO
DECREASE FROM W-E WITH TIME ACROSS THIS AREA DUE TO VEERING OF
POSTFRONTAL WINDS AND WEAKENING OF MIDLEVEL FLOW. MODIFIED RUC
SOUNDINGS SUGGEST THIS ACTIVITY IS MOVING INTO ENVIRONMENT OF
RELATIVELY MAXIMIZED MIDLEVEL LAPSE RATES -- 7-8 DEG C/KM.
THIS...COMBINED WITH SFC DEW POINTS 50S F...SUPPORTS MLCAPE IN
500-1000 J/KG RANGE. LIMITING FACTORS WILL INCLUDE LACK OF MORE
ROBUST MOISTURE/THETAE...AS WELL AS NEBULOUS BOUNDARY LAYER FOCI
AWAY FROM FRONT AND WEAK CONVERGENCE ALONG IT.
..EDWARDS.. 09/27/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...MQT...GRB...DLH...ARX...MPX...
LAT...LON 45678808 45279034 45249154 45929232 47589211 48219181
48199173 48109173 48069156 48079124 48249086 48079075
48129056 48099051 48109007 47998997 48038978 47968939
47218812 45678808
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