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ACUS11 KWNS 200843
SPC MCD 200843

Mesoscale Discussion 0073
NWS Storm Prediction Center Norman OK
0243 AM CST Tue Feb 20 2018

Areas affected...portions of Iowa into southeast Minnesota and
portions of western Wisconsin

Concerning...Freezing rain

Valid 200843Z - 201145Z

SUMMARY...Freezing rain/mixed wintry precipitation will continue
spreading northeast across portions of Iowa and adjacent southeast
Minnesota, and spreading into western/southwestern Wisconsin over
the next 1-2 hours.

DISCUSSION...Latest radar loop shows a band of heavier precipitation
-- including occasional/embedded lightning -- continuing to shift
northeast across central and eastern Iowa and adjacent southeast
Minnesota at this time.  The precipitation is occurring within a
zone of warm advection, with QG ascent bolstered by a compact vort
max whose center of circulation is indicated in water vapor imagery
to be shifting into southwest Iowa at this time.  While the rather
fast motion of the precipitation field is limiting duration of
heavier amounts at any one locale, briefly moderate to heavy rain --
where surface temperatures are largely in the upper 20s to low 30s
-- will continue to allow icing to occur.

Latest model runs -- in particular several hi-res CAMs -- suggest
steady or even diminishing precipitation intensity over the next few
hours.  In addition, an axis of above-freezing surface temperatures
are apparent along the Mississippi Valley northward into southwest
Wisconsin/northeast Iowa.  Still, moderate to briefly heavy freezing
rain will occur across portions of the area -- as highlighted by the
MCD graphic -- over the next few hours.

..Goss.. 02/20/2018

...Please see for graphic product...


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