Temperatures remain just above freezing in most areas limiting the impacts.
ST. LOUIS — A Weather Impact Alert is in effect until 4 a.m. Monday.
SUNDAY EVENING UPDATE: The cold rain and wet snow is moving into the region this evening. Temperatures drop as precipitation moves in and some sleet or graupel has been noted as the atmosphere cools as the precipitation begins. A wintry mix of cold rain and at times wet snow along with some accumulating snow north of Interstate 70 is possible through about 3 a.m. Monday. Some minor impacts on travel are possible. Along and south of I-70, there will be rain or a rain/snow mix with locally heavier rainfall.
By Monday’s early commute, only lingering light rain or drizzle is expected with roads being damp but not drenched.
This is not a big winter event.
Highs climb back into the 60s on Tuesday and stay mild the rest of the week. It also looks active, with multiple rounds of rain (and possibly a few rumbles of thunder late week). Severe weather is not a high-confidence threat right now, but we’ll keep an eye on how the end-of-week system evolves.
Click here for the full Weather Impact forecast.
5 On Your Side meteorologists will use Weather Impact Alerts to let you know when impactful or dangerous weather is expected as soon as there is confidence in disruptive weather happening in our area.
Download the free 5 On Your Side app to get the latest watches and warnings and track conditions live with our interactive radar. Use the links below to download now.
5 On Your Side news app
iPhone | Google Play
To watch 5 On Your Side broadcasts or reports 24/7, 5 On Your Side is always streaming on 5+. Download for free on Roku or Amazon Fire TV.
Timing: Sunday evening into Monday morning is the window to watch, with the main concern being roads turning slick and the need to check updated forecasts.
Where snow is more likely: The better accumulating light snow potential remains north of Interstate 70, consistent with the colder air being deeper and more “locked in” there. If you’re in our northern Missouri counties or west-central Illinois, that’s the corridor where travel impacts have a higher ceiling if the system trends colder or the snow band sets up a bit farther south. This is subject to change, but accumulating snowfall is possible in some locations toward the north.
Why this forecast is tricky (and why it may change)
This isn’t a simple “all snow” storm. It’s a layer-cake atmosphere — cold air near the ground with a warmer layer aloft trying to push in. That creates three big forecasting issues:
- Precipitation type: A slightly stronger warm layer favors sleet/freezing rain; a deeper cold layer favors more frozen precipitation. A tiny temperature shift a few thousand feet up can change everything, and forecast models struggle with these details this far out.
- Storm track: A north/south wobble of the system shifts the heaviest band and the rain-to-snow line county-to-county, which is very common in the days leading up to the system’s arrival.
- Road impacts: Even if air temps hover near freezing, road temps can lag (or crash quickly after dark). Precipitation rates matter, too — heavier rates can overcome marginal temperatures faster than light rates.
One of the main problems we will have in forecasting this system, as mentioned above, is the significant cold air that’s really lacking in the region. Even at it’s coldest, hundreds of miles away, we are still only 5-10 degrees below freezing. That’s more in line with where the precipitation type won’t be in question. For us locally, while I expect us to get near or below freezing for at least a couple of hours, the southern extent of that really comes into play as we forecast exactly what’s going to occur Sunday into Monday.
The way this looks right now, through midday Thursday, is as stated above. There is a zone in question that is yet to be determined by just how far the southern extent of cold air actually moves. While this area in pink may have multiple rounds and types of a wintry mix, I tend to think the actual temperature will struggle to get to or below freezing for too long. But that doesn’t mean we won’t have a few travel problems and localized impacts overnight Sunday into Monday.
What you should do now
If you have Sunday night plans or a Monday morning commute, have a Plan A/Plan B mindset. The “rain/snow line” near St. Louis is why we’re emphasizing staying tuned: as new data comes in, we’ll fine-tune timing of the changeover, how far south the snow line gets and whether the metro’s biggest threat is brief slick spots or something more widespread. Right now, the odds of travels impacts appear to be limited to mostly roads being wet.
We’ll update this Weather Impact Alert as confidence increases — especially on where the most impactful band sets up. Keep checking forecasts through the weekend, and make sure you can receive alerts in case advisories or warnings are issued.