Severe Storm Outlook Narrative (AC)
Issued by NWS
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
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.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 42248945 42528911 42608864 42588815 42468789 41978769
41688738 41698684 41598640 41338614 40748637 40728794
40928879 41638945 42248945