Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 172320
SWOMCD
SPC MCD 172320
MIZ000-180115-

Mesoscale Discussion 1518
NWS Storm Prediction Center Norman OK
0620 PM CDT Thu Aug 17 2017

Areas affected...Lower Michigan

Concerning...Severe potential...Watch unlikely

Valid 172320Z - 180115Z

Probability of Watch Issuance...5 percent

SUMMARY...The severe-weather potential has lessened across Lower
Michigan, with this trend expected to persist this evening,
resulting in a likely removal of all or most severe probabilities
across Lower Michigan in the upcoming 01Z Convective Outlook.

DISCUSSION...Mid-level winds across much of Lower MI have veered to
southwesterly or westerly in the wake of a shortwave trough that has
moved east and was located over Georgian Bay and adjacent Ontario.
A similar veering of low-level winds was also noted across western
and southern Lower MI per trends in area WSR-88D VADs.  Residual
moisture (surface dew points in the upper 60s to lower 70s) and
marginal instability is sufficient for an ongoing broken band of
showers and an occasional thunderstorm along an eastward-moving zone
of convergence, given the presence of south-southeasterly low-level
winds yet across east-central and northern Lower MI.  Deep-layer
shear is strong to support storm organization, while forcing for
ascent attendant to a progressive mid-upper level cyclone, currently
located over Upper MI, could prove sufficient for a few additional
showers/thunderstorms across eastern/northern Lower MI.  However,
weak midlevel lapse rates and deep-layer ascent are expected to
weaken further as low-level winds continue to veer.  Given that and
the track of the mid-upper level cyclone being to the north of Lower
MI, storm potential will be greatly reduced.

..Peters/Edwards.. 08/17/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DTX...APX...

LAT...LON   44858447 45438511 45788460 45388360 44668323 44558323
            44268327 44098318 44068278 43498258 42588258 42178319
            42168361 42518385 43308400 44168418 44438439 44858447



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