We’re boosting our Chicago accumulation forecasts further
We’re boosting our Chicago accumulation forecasts further, a foot or more of snow likely in parts of the city—much lighter amounts south
The early onset of snow suggests even higher storm snow totals are likely in the city. Expectations precipitation would start as a rain/sleet mixture in the northern suburbs due to a layer of warm air aloft have NOT materialized suggesting northeast winds have injected a layer of drier air in the lower atmosphere producing evaporative cooling there. That’s why snow has begun as soon as it has. This means assumptions that the first hours of this storm’s precipitation would come down as liquid or a mix must be updated and that moisture must be added to our predicted snow tally. As a result, it now appears likely 8-14” will fall from Chicago north and west. The presence of potential thunderstorms could lead to locally higher totals. Our latest in-house RPM (Rapid Precision Mesocale) model forecast now puts totals at 13” at O’Hare and 10” at Midway. The University of Wisconsin NMS model is even suggesting 12-18” totals in portions of northern Illinois.
Thus a major winter storm, by far this winter’s biggest to date, looks likely to produce serious travel problems well into Wednesday. We’ll update as new information becomes available.
Tom Skilling
Chief Meteorologist, WGN-TV/Chicago Tribune