MESO: Mesoscale Discussion 1870

ACUS11 KWNS 102200
SWOMCD
SPC MCD 102200
MIZ000-WIZ000-110030-

MESOSCALE DISCUSSION 1870
NWS STORM PREDICTION CENTER NORMAN OK
0500 PM CDT TUE SEP 10 2013

AREAS AFFECTED...PORTIONS OF CNTRL/ERN WI...NRN LOWER MI...SRN/ERN
PARTS OF THE UPPER PENINSULA OF MI...ADJACENT LAKES MICHIGAN AND
HURON

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 102200Z - 110030Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...AN ISOLATED SVR STORM OR TWO CANNOT BE RULED OUT INTO THE
EVENING...HOWEVER THE ISSUANCE OF A WW IS NOT NEEDED.

DISCUSSION...AREA VWP DATA INDICATE 30-60 KT OF NEARLY
UNIDIRECTIONAL WLY FLOW ABOVE 2 KM AGL...WITHIN THE BASE OF A BROAD
AREA OF STRONG MID-LEVEL CYCLONIC FLOW GLANCING THE REGION. DEEP
FORCING FOR ASCENT SHOULD BE MODEST THROUGH THE
EVENING...HOWEVER...OWING TO THE LACK OF DIRECT INFLUENCE FROM
STRONG MID-LEVEL PERTURBATIONS PER WATER VAPOR IMAGERY.
REGARDLESS...A BRANCH OF ENHANCED MID-LEVEL MOISTURE EXTENDS ENEWD
INTO THE REGION FROM THE WRN MONSOONAL MOISTURE PLUME. THIS MAY
SHELTER UPDRAFTS FROM ENTRAINMENT PROCESSES ASSOCIATED WITH
INCIPIENT CONVECTION DEVELOPING ON THE WARMER SIDE OF A DIFFERENTIAL
HEATING ZONE ARCING FROM THE ERN UPPER PENINSULA OF MI TO CNTRL WI.
VERTICAL CIRCULATIONS ALONG THIS BOUNDARY WILL LIKELY AUGMENT THE
CIRCULATIONS ATTENDANT TO A QUASI-STATIONARY FRONT EXTENDING FROM
NEAR THE MIDPOINT OF LAKE SUPERIOR TO AROUND LA CROSSE WI TO FOSTER
SUFFICIENT LIFT FOR ISOLATED TO WIDELY SCATTERED STORMS THROUGH THE
EVENING.

THE STRONGEST STORMS SHOULD BE FOCUSED JUST S OF THE DIFFERENTIAL
HEATING ZONE...THOUGH ISOLATED STORMS COULD EVOLVE FROM DEEPER PBL
CIRCULATIONS FARTHER S AND INLAND. THE PRESENCE OF MARGINAL TO
LOCALLY MODERATE INSTABILITY AMIDST STRONG DEEP SHEAR MAY FOSTER A
FEW ORGANIZED CONVECTIVE STRUCTURES. AN ISOLATED SVR WIND GUST OR
TWO CANNOT BE RULED OUT...AND SUCH ACTIVITY COULD BE STEERED ACROSS
PARTS OF LAKES MICHIGAN AND HURON. HOWEVER...THE ONSET OF NOCTURNAL
COOLING/BOUNDARY LAYER STABILIZATION SHOULD ABBREVIATE THE WINDOW OF
OPPORTUNITY FOR STRONGER STORMS...AND WEAK MID-LEVEL FORCING FOR
ASCENT AND POOR MID-LEVEL LAPSE RATES SHOULD PREVENT A MORE
SUBSTANTIAL SVR THREAT FROM EVOLVING.

..COHEN/HART.. 09/10/2013

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

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

LAT...LON 44079063 45458832 46498580 46378435 45848366 44938329
44158443 43478709 43369006 44079063

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