Weather Impact Alert: Mix of rain and snow ending overnight

ST. LOUIS — A Weather Impact Alert is in impact till 4 a.m. Monday.

SUNDAY EVENING UPDATE: The chilly rain and moist snow is shifting into the area this night. Temperatures drop as precipitation strikes in and some sleet or grain has been famous because the ambiance cools because the precipitation begins. A wintry combine of chilly rain and at occasions moist snow together with some accumulating snow north of Interstate 70 is feasible via about 3 am Monday. Some minor impacts on journey are attainable. Along and south of I-70, there will likely be rain or a rain/snow combine with domestically heavier rainfall.

By Monday’s early commute, solely lingering mild rain or drizzle is anticipated with roads being damp however not drained.

This shouldn’t be a giant winter occasion.

Highs climb again into the 60s on Tuesday and keep delicate the remainder of the week. It additionally seems to be lively, with a number of rounds of rain (and probably a couple of rumbles of thunder late week). Severe climate shouldn’t be a high-confidence menace proper now, however we’ll control how the end-of-week system evolves.

Click here for the complete Weather Impact forecast.

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Timing: Sunday night into Monday morning is the window to observe, with the primary concern being roads turning slick and the necessity to examine up to date forecasts.

Where snow is extra possible: The higher accumulating mild snow potential stays north of Interstate 70, per the colder air being deeper and extra “locked in” there. If you are in our northern Missouri counties or west-central Illinois, that is the hall the place journey impacts have a better ceiling if the system tendencies colder or the snow band units up a bit farther south. This is topic to vary, however accumulating snowfall is feasible in some areas towards the north.

This is not a easy “all snow” storm. It’s a layer-cake ambiance — chilly air close to the bottom with a hotter layer aloft making an attempt to push in. That creates three large forecasting points:

1. Precipitation sort: A barely stronger heat layer favors sleet/freezing rain; a deeper chilly layer favors extra frozen precipitation. A tiny temperature shift a couple of thousand toes up can change the whole lot, and forecast fashions wrestle with these particulars this far out.
2. Storm monitor: A north/south wobble of the system shifts the heaviest band and the rain-to-snow county-to-county line, which is quite common within the days main as much as the system’s arrival.
3. Road impacts: Even if air temps hover close to freezing, street temps can lag (or crash shortly after darkish). Precipitation charges matter, too — heavier charges can overcome marginal temperatures sooner than mild charges.

One of the primary issues we may have in forecasting this technique, as talked about above, is the numerous chilly air that is actually missing within the area. Even at it is coldest, tons of of miles away, we’re nonetheless solely 5-10 levels beneath freezing. That’s extra in keeping with the place the precipitation sort will not be in query. For us domestically, whereas I anticipate us to get close to or beneath freezing for no less than a pair of hours, the southern extent of that basically comes into play as we forecast precisely what is going on to happen Sunday into Monday.

The manner this seems to be proper now, via noon Thursday, is as acknowledged above. There is a zone in query that’s but to be decided by simply how far the southern extent of chilly air truly strikes. While this space in pink could have a number of rounds and sorts of a wintry combine, I are inclined to assume the precise temperature will wrestle to get to or beneath freezing for too lengthy. But that does not imply we cannot have a couple of journey issues and localized impacts overnight Sunday into Monday.

If you’ve got Sunday evening plans or a Monday morning commute, have a Plan A/Plan B mindset. The “rain/snow line” close to St. Louis is why we’re emphasizing staying tuned: as new information is available in, we’ll fine-tune timing of the changeover, how far south the snow line will get and whether or not the metro’s greatest menace is transient slick spots or one thing extra widespread. Right now, the chances of journey impacts look like restricted to largely roads being moist.

We’ll replace this Weather Impact Alert as confidence will increase — particularly on the place essentially the most impactful band units up. Keep checking forecasts all through the weekend, and ensure you can obtain alerts in case advisories or warnings are issued.