ST. LOUIS, Mo. — Colder air is now in control with spotty light rain showers likely the rest of today into tonight. Some mixing with snow and sleet may occur northwest of St. Louis this evening. I am expecting little if any impact to travel as a result. This will be quick and temperatures are very marginal and the ground is quite warm. The same holds for tonight, only spotty very light wintry mix is on the table. I don't have any big concerns for the morning rush hour Wednesday.
A Winter Storm Watch is in effect from the St. Louis area to the northwest Wednesday. The heaviest snowfall (2-5 inches) should be north and northwest of St. Louis County. We should see a mix of sleet and snow in a narrow band on the southeast flank of the heavy snow. That appears to be set for the southeast side of I-44 up into St. Louis County and then northeast from there.
Sleet will have a significant impact on the snowfall totals in St. Louis County and points southeast, holding numbers down to about two inches. It is quite possible that areas from Alton to St. Peters, St. Charles, and Augusta in Missouri could see upwards of 5 inches. But, less than 10 miles to the south totals may be 2 inches or less across much of St. Louis County. A shift of even 5 or 10 miles in that track south or north will make a big difference in how much actually falls. Either way, 2" of sleet and snow will have a similar impact on roads as up to 5 inches of wet snow. The bottom line is that tomorrow afternoon's drive will be the roughest of the day.
Start times for Wednesday's precipitation are still on track for late morning southwest of St. Louis, between 10 am and 1 pm for the St. Louis area and after 1pm further northeast.
I have to stress there will be a razor-thin cut-off between the bigger snows and minimal snow/more sleet. That line is aiming for the St. Louis and St. Charles County line.
Also in play for our friends to the south will be freezing rain. This will be largely be limited to grassy areas, trees, elevated surfaces or parked cars. But, as always, when there is freezing rain you have to assume some ice in spots on the ground which could cause issues.
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