(11:30PM - 1/18/19 - Just a quick update as our winter storm continues to ramp up across northern portions of Illinois as we reach the midnight hour across the Midwest. Over the past several hours, snow has quickly filled into portions of northern Illinois with accumulations wasting no time as temperatures are well into the 20's (low to mid 20's across much of that area). Also, visibility has dropped to a 1/2 mile in several spots over the last few hours, indicative of moderate to borderline heavy snowfall rates. Several places across northern Illinois, including the metro area are already above 1" of snow so far and will continue to ramp up over the next several hours.
As previously mentioned, expect snow to continue through the overnight hours and lasting through late morning across northern Illinois before it pushes off to the southeast. It will however continue across central Illinois and even portions of southern Illinois into the afternoon and evening hours as the area of low pressure runs northeast into the Ohio River Valley with colder air advecting into downstate.
Another big story overnight and more so during the morning and afternoon hours tomorrow will be the strengthening north and northeast winds across all of Illinois as the pressure gradient tightens between high pressure to our northwest and low pressure to our southeast. This will mean wind gusts across much of the state reaching or exceeding 35mph during the day tomorrow.
Below is our latest TAM snowfall forecast map across Illinois, which has only had minor changes. This map also includes lake effect snow which will become the story across northeast Illinois later Saturday and into Sunday.