The "additional details" section clears it up. WWA covers the initial burst, WSW covers Friday evening with the main band.
ADDITIONAL DETAILS...A burst of accumulating snow is expected mid
to late Friday morning through early afternoon. The snow during
this period may briefly fall at a rate of up to an inch per hour
and make for slick travel conditions. Then, later Friday afternoon
and evening, an intense band of heavy lake effect snow will
develop over southern Lake Michigan, and may impact portions of
central and southern Cook county near the lake for a period Friday
evening before focusing eastward into northwestern Indiana later
Friday night. While the residence time of this lake effect band
over Cook county may only be 3 to 5 hours, the potential for heavy
snow rates of 2+ inches per hour could result in localized
accumulations exceeding 6 inches, particularly near the lake from
the city southward.