Snow chances increase; blast of arctic air expected Christmas Eve




Light snow continued to dust the area into Saturday

Snow cover likely to expand in coming week as polar air settles across much of nation

As of midnight Saturday, 44.1% of the continental U.S. was covered by at least 1″ of snow. Much of this past week’s increase resulted from a massive storm system that took a full week to cross the continent, leaving in its wake snow depths of 10+” across the northern Plains and upper Midwest. Lighter amounts extended south into northern Illinois and NW Indiana.

Most forecast guidance is suggesting a potential for another winter storm to materialize the latter part of this week.  The GFS model from the National Weather Service keeps Chicago on the west and north fringe of greatest snowfall though lake enhancement may inflate forecast totals.

At this point models differ widely on the timing and location of heaviest snowfall. This map reflects a consensus of expected snow depth expected by 6 PM Friday. This places much of Chicago in a region of 6″ snow depth. 

Probability of a white Christmas in Chicago has increased

Model forecast probability of receiving 4 or more inches of snow in the 12 hours ending at 6 PM Friday based on NWS GFS model. Though higher probabilities are indicated east of Chicago, the possibility of lake enhanced snowfall may inflate the numbers shown. The same graphic from Friday’s model run showed probabilities of around 20%.

Blast of arctic air expected by Christmas Eve

Unlike the uncertainty surrounding forecast snowfall later this week, there is a high degree of agreement among forecasts that a surge of very cold air will circulate in from the Arctic Friday and Saturday.  Arrows on this map of forecast temperatures at 6 AM Saturday, 12/24 represent low-level wind flow.   Subzero temps may reach the Ohio Valley, with freezing air reaching the Gulf Coast.