Timing the winter storm: When will the St. Louis area see snow and ice?

ST. LOUIS - An intense winter storm system will roll through the St. Louis region this weekend. A mix of heavy snow and ice is expected across the entire St. Louis metro from Saturday evening to Monday morning, primarily on Sunday.

Here's a closer look at a timeline of snow and ice impacts...

Saturday evening

A Winter Storm Warning officially takes effect at 10 p.m. Saturday. Between 10 p.m. and midnight, snow accumulations are expected to begin for many Greater St. Louis Area counties around and north of the Interstate 70 corridor.

Around midnight, sleet is expected to arrive for many St. Louis-area counties near the Interstate 44 corridor, though the potential for snowfall in the southern counties remains uncertain.

For areas a little more north and west of the St. Louis metro, such as Kirksville and Columbia, snow could possibly begin a few hours earlier.

Sunday morning

Heavy winter storm impacts will build overnight. From midnight to 7 a.m., several inches of snow could fall for the more northern counties of the St. Louis metropolitan area and mid-Missouri.

From the I-70 corridor to roughly the southern points of Crawford, Washington, St. Francois, and Ste. Genevieve counties, more sleet than snow is expected during the overnight hours.

Freezing rain is most likely to accumulate around Dent, Reynolds, Iron, and Madison counties in Missouri, though there could be some freezing rain impacts as north as Jefferson County. It appears from around 2 a.m. to noon Sunday could see the strongest impacts. These counties are possibly at risk of power outages as freezing rain accumulates.

The storm system will progress east toward the Illinois side of the St. Louis metro. Snow could begin around the Interstate 64 corridor in Illinois around midnight of 1 a.m. Anywhere south of that could see various snow and sleet impacts beginning around 3 or 4 a.m.

Sunday afternoon and evening

For much of Sunday morning and early afternoon, St. Louis-area counties north of I-70 are most likely to see snow, counties between I-70 and I-44 are most likely to see sleet, and counties south of I-44 will be most at risk for freezing rain.

Generally speaking, more snow will mean fewer ice chances, while more ice will mean fewer snow chances.

The storm system is expected to take a notable turn by around 4 p.m. Sunday for much of the St. Louis region. Snowfall will move from the northwest counties to the southeast counties of the St. Louis metro. Most Missouri and Illinois counties near St. Louis will see some amount of snowfall, possibly several inches, between 4 p.m. to midnight Monday.

Thundersnow, a winter weather phenomenon typically characterized by the occurrence of thunder and lightning during a snowstorm, is also possible during the late afternoon and early evening hours. This usually happens around the same atmospheric conditions that produce non-winter thunderstorms, but with the presence of cold air and snow instead of rain. Timing for possible thundersnow remains to be determined.

Monday

The Winter Storm Warning will end by 6 a.m. Monday. Some snowfall may linger from Sunday into Monday, but the winter storm system is expected to weaken after midnight.

By Monday, current predictions from FOX 2's weather team call for...

• 8-10 inches of snow for counties north of Interstate 70
• 4-8 inches of snow and measurable sleet for counties closest to St. Louis and of similar latitudes
• Up to half an inch of ice and 2-5 inches of snow for counties south of Jefferson County and near the I-44 corridor.

MoDOT and IDOT are asking the public to consider limiting driving outdoors during the heaviest of winter weather impacts on Sunday.

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