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ACUS11 KWNS 110059
SPC MCD 110059

Mesoscale Discussion 1875
NWS Storm Prediction Center Norman OK
0659 PM CST Sat Dec 10 2016

Areas affected...Portions of northern Illinois...far southern
Wisconsin...and northwest Indiana

Concerning...Heavy snow

Valid 110059Z - 110700Z

SUMMARY...Occasional snowfall rates up to one inch per hour will be
possible through the overnight hours across the discussion area.
Moderate to perhaps brief heavy snow will persist across the
Chicagoland area and expand eastward into northwest Indiana over the
next 4-6 hours.

DISCUSSION...Regional radar imagery indicates multiple bands of
snowfall are overspreading northeast Illinois this evening, in
response to strengthening warm-air advection from the surface
through about 4 km. Recent KLOT and KILX VAD wind profile data
illustrate a steadily veering wind profile through this layer,
suggesting that isentropic-ascent-induced bands of snowfall should
persist into the overnight hours. While there is some uncertainty
where the heaviest mesoscale banding could organize, portions of the
Chicagoland area will potentially be impacted by periods of heavier
snowfall rates (up to an inch per hour) through the overnight.
Forecast soundings indeed depict a dendritic growth zone through
several kilometers of the mid levels, favorable for higher
snow-to-liquid ratios. Over time, as the strongest warm-air
advection shifts east tonight, heavier snowfall will subsequently
expand eastward into northwest Indiana.

..Picca/Cohen.. 12/11/2016

...Please see for graphic product...


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