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ACUS11 KWNS 120906
SPC MCD 120905

Mesoscale Discussion 0035
NWS Storm Prediction Center Norman OK
0305 AM CST Thu Jan 12 2017

Areas affected...portions of central and northeast IL...northwestern
IN...Michiana...and southern Lower MI

Concerning...Freezing rain

Valid 120905Z - 121500Z

SUMMARY...The onset of freezing rain is expected over central IL
during the late overnight and move northeastward into portions of
northern IN prior to sunrise and southern Lower MI this morning.
Appreciable freezing rain rates will be spotty with elevated
convection but may range 0.05-0.10 inch per 3 hours.

DISCUSSION...Radar mosaic and lightning data around 09 UTC shows an
expanding precipitation shield near the MO/IL/IA border associated
with weak elevated thunderstorms.  The activity near the MS river is
likely associated with the leading edge of stronger mid-level ascent
/dcva/ associated with a east-northeastward moving shortwave trough
analyzed over the central Great Plains.  This feature will quickly
move downstream towards the southern Lake MI vicinity by 15 UTC.

In the low levels, surface analysis shows the southeast progression
of cold air with the freezing line over central IL and far
southwestern MI.  Low-level cold air advection will result in the
discussion area falling at or below 32 deg F during the period and
prior to the beginning of precipitation.  Forecast soundings show
the thermal stratification of a shallow sub-freezing layer beneath a
warm layer around H85.  Moderately steep H7-H5 lapse rates around 7
deg C per km and a saturating profile will yield weak buoyancy
/100-200 J per kg MUCAPE/.  As a result of the increased forcing for
ascent and columnar saturation, freezing rain is forecast to begin
near the MS river and spread downstream to the east-northeast during
the overnight and early morning.  Forecast soundings also imply the
heaviest rates will occur in a time window around 11-13 UTC near
Pontiac, IL, 12-15 UTC near South Bend, IN, and 14-15 UTC near
Jackson, MI.  Given the convective character of the forecast
precipitation, spotty amounts are expected but freezing-rain rates
of 0.05-0.10 inch per 3 hours are possible.

..Smith.. 01/12/2017

...Please see for graphic product...


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