Weather Impact Alert: Mix of rain and snow ending overnight

Scheduled Tribe. LOUIS – A Weather Impact Warning is in effect until 4 a.m. Monday.

Sunday evening update: Cold rain and wet snow moving into the area this evening. As the rainfall increases, the temperature drops and the atmosphere becomes cooler as the rainfall begins and some hailstorms have also been observed. A wintry mix of freezing rain and sometimes sleet, along with some accumulating snow, is possible north of Interstate 70 until about 3 a.m. Monday morning. Some minor impacts on travel are possible. Along and south of I-70, there will be locally heavy precipitation with rain or a rain/snow mix.

By Monday morning, only light rain or drizzle is expected, with roads being moist but not wet.

This is not a big winter event.

Highs reach around 60 on Tuesday and remain mild the rest of the week. It also looks active, with several rounds of rain (and possibly a few thunderstorms through the end of the week). Severe weather is not a high-confidence threat right now, but we’ll keep an eye on how the system develops over the weekend.

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Timing: Sunday evening through Monday morning is a good time to watch, with the main concern being slow roads and the need to check updated forecasts.

Where snow is more likely: The potential for better accumulating light snow remains north of Interstate 70, consistent with the cold air being deeper and more “locked in” there. If you’re in our northern Missouri counties or west-central Illinois, this is the corridor where the extent of travel impacts are greater as the system cools or a snow band sets in a little farther south. This is subject to change, but snowfall is possible in some places further north.

This is no ordinary “complete blizzard”. It’s a layer-cake atmosphere – cold air near the ground and a warm layer trying to push upward. This raises three major forecasting issues:

1. Precipitation Type: A slightly stronger warm layer promotes sleet/freezing rain; The deep cold layer promotes more freezing precipitation. A small change in temperature a few thousand feet up can change everything, and forecast models still struggle with these details.
2. Storm Track: The north/south wobble of the system shifts the heaviest bands and rain-to-snow lines from county-to-county, which is very common in the days before the system’s arrival.
3. Road effect: Even if the air temperature is near zero, road temperatures can slow down (or crash rapidly) after dark. Precipitation rate also matters – heavy rates can overcome marginal temperatures faster than light rates.

As mentioned above, one of the main problems we face in forecasting this system is the significant cold air that is really lacking in this region. Even in the coldest conditions, hundreds of miles away, we are still only 5-10 degrees below zero. This is consistent with the situation where the type of precipitation would not be in question. For us locally, while I expect we’ll be near or below freezing for at least a few hours, the southern edge of it really comes in handy as we predict exactly what’s going to happen Sunday through Monday.

As mentioned above, this is what it looks like now as of Thursday afternoon. One area in question is that it has not yet been determined how far the southern boundary of the cold air actually runs. Although there may be many rounds and types of wintry mix in this area of ​​pink, I think actual temperatures will struggle to fall at or below zero for very long. But that doesn’t mean we won’t have some travel issues and local impacts from Sunday to Monday.

If you have plans for Sunday night or a Monday morning trip, have a Plan A/Plan B mentality. We’re stressing caution due to the “rain/snow line” near St. Louis: As new data comes in, we’ll fix the timing of the change, how far south the snow line goes and whether the metro’s biggest threat is a brief sleet spot or something more widespread. At present, the possibility of impact on travel is mostly limited to wet roads.

We will update this weather impact warning as confidence increases – particularly where the most impactful band is established. Keep checking the forecasts throughout the weekend, and make sure you can receive alerts if advisories or warnings are issued.